Subaru Noobie FAQs.

This was posted on various forums , but is nice to have handy.
Source , www.nasioc.com and www.northursalia.com... This thread will be open for changing.

GENERAL

About Subaru

In February 1954, FHI announced its prototype passenger car called the P-1. The P-1, named the Subaru 1500 the following year, used the first Japanese-manufactured monocoque body. This passenger car provided excellent riding comfort and driving stability with its front-wheel wishbone-type independent suspension; a coil spring and double-action oil damper combination, and rear-wheel rigid axle suspension with a three-leaf spring and double-action oil damper combination. Unfortunately, sales had to be suspended because of difficulties in funding the factory equipment and sales network. Nevertheless, this vehicle proved to be of great value in the later developments of the Subaru 360 and Subaru 1000. That was the starting point for Subaru.

But why "Subaru"? Subaru is the name of a star cluster in the Taurus constellation, which is called Pleiades in the West. Six of its stars are visible to the naked eye, but about 250 bluish stars can be seen if one uses a telescope. Credit for naming the company goes to Kenja Kita, the first president of Fuji Heavy Industries. As Fuji Heavy Industries had just taken over 5 of 12 companies resulting from the breakup of the old Nakajima Aircraft Company, Kita saw this unique name as the ideal symbol to express the unification of these 5 Fuji companies -- "Subaru".


About Subaru Tecnica International

Subaru Tecnica International (STi) was founded in April 1988 by Fuji Heavy Industries, Ltd. Its purpose was promote Subaru cars around the world by participating in motorsports. STi identified rallying and endurance speed records as two types of motorsports that Subaru should participate in. The newly launched Legacy set two world records and 13 international records in the 100,000km FIA World Speed Record in January 1989. The World Rally Championship project evolved from Subaru's involvement in Japanese rallying but became a full scale factory effort when STi joined forces with the British-based Prodrive company. The initial objective was to pose a serious challenge to the established manufacturer teams competing in the World Rally Championship.


Q: What is the "break in period" and if I don't do it, will it hurt my car?
A: The break in period for Subaru is the first 1,000 miles. During this time, you should vary the RPM and speed of the vehicle as much as possible, without racing the engine or exceeding 4,000 rpms unless needed in an emergency situation. The idea is that this allows the engine to wear-in under a variety of conditions without abusing it, giving the seals time to expand and do their job. This is a hot topic of debate as to being necessary or not, though it is strongly recommended by Subaru.

Q: Where can I find a good shop manual, and why are the Subaru shop manuals so expensive?
A: There are no Chilton's or Haynes manuals yet available for the Impreza RS or WRX. The Legacy GT manual is of some help to RS owners, as the Legacy GT does share the same engine. The factory service manuals are the very best thing to have, as they are the same manuals the service department uses when working on your vehicle and are full of the most accurate, up to date information about your car.

Q: Will installing aftermarket parts void my warranty?
A: It is up to the manufacturer to prove that the aftermarket parts directly caused the problem that is under warranty consideration in order to deny warranty work. They cannot void the whole warranty, nor deny warranty work on the alternator for having an aftermarket suspension. However, if your brake rotors warp and you have aftermarket pads, likely expect a warranty claim on the rotors to be denied. There is a federal statue know as the Moss-Magnusson Warranty Act that can be used in defense of a legitimate denied warranty claim.

ENGINE AND DRIVETRAIN

Q: What is a proper way to break in a new car or a car with a brand new engine?
A: The break in period for Subaru is the first 1,000 miles. During this time, you should vary the RPM and speed of the vehicle as much as possible, without racing the engine or exceeding 4,000 rpms unless needed in an emergency situation. The idea is that this allows the engine to wear-in under a variety of conditions without abusing it, giving the seals time to expand and do their job. This is a hot topic of debate as to being necessary or not, though it is strongly recommended by Subaru.


Q: Where do I wire-in my Air/Fuel Sensor?
A: Most Air/Fuel gauges are designed for narrow-band oxygen sensors (0 to 1 volt). On a WRX, you would tap into ECU connector B135 (28 pin connector) wire 17 (it is solid white). On an 98 RS, it is wire 23 (yellow/blue wire) on the one big connector on the ECU. For 99+ RS, it is wire 18 on connector B136 (30 pin connector) and is solid white in color.


Q: Where do I tap in for my EGT sensor?
A: Conventional wisdom dictates to install the EGT probe 4" away from the hottest running cylinder. On a naturally aspirated vehicle, it can be installed just below the collector on either the driver side or passenger side exhaust header. On a turbocharged vehicle, it is generally advised to place it 4" from the turbocharger instead.


Q: Every time I shift, I hear this "clunk" from the back of my Impreza. Is it normal?
A: Yes, your rear differential is making that noise. It can also be caused my slight free play movement of the driveshaft.


Q: When my car is in gear, I hear a distinctive whine from where the shifter is. Is it normal?
A: Yes, your center differential is making this noise. It is being transferred through the shifter. Cars with aftermarket shifter kits tend to have more/louder noise, due to harder shifter bushings.


Q: What is clutch shudder and how can it be fixed?
A: Clutch shudder is a sometimes violent vibration when releasing the clutch pedal, and is generally worse when it is cold and damp. It can be attributed to a glazed clutch disk, a weak pressure plate, or condensation on the clutch disk face. It is generally a very difficult problem to replicate for the dealership, and not all dealerships will even acknowledge that it is a problem. The most effective way to prevent clutch shudder is to upgrade/replace the clutch disk and pressure plate. Of course, this is an expensive proposition if it is not covered by the factory warranty.


Q: I hear a "ticking" sound after shutting the engine down. What is causing this?
A: Due to the expansion and contraction of the metals used in the manufacture of the exhaust system, you may hear a crackling sound coming from the exhaust system for a short time after the engine has been switched off. This sound is normal.


Q: Can I used leaded fuels in my car?
A: Only if you want to replace an expensive set of O2 sensors and ruin your catalytic converter.


Q: What is a dogbox?
A: The "dog" in dogbox does not refer to the gears at all, but the the shifting mechanism. You can have a dogbox without straight cut gears. And you you can have a straight cut gearbox with synchronizers. Production car gearboxes have helical cut gears to keep them quiet. Straight cut teeth are ususally bigger but there is backlash and the teeth knocking together produce the distinctive gear whine. Production gearboxes also use synchronizers to provide smooth, quiet shifting. The synchro's job is to "grab" the gear when you are shifting and match it to the same speed as the driven shaft to provide a smooth silent shift with no grinding. This happens as you move the lever into the gate for that particular gear. The trouble with synchros is they slow down the shifting process and they have little teeth which aren't so strong compared to the mysterious "dogs". The engaging teeth on the gears are equally small so you could potentially strip all the synchro engaging teeth off the gear and have no more drive in that gear even though all the gear teeth are in perfect condition! A dogshift box does without the synchronizers. Instead you have 6 or 8 big dog "teeth" on the gear. On the shift slider you may have a corresponding number of "slots" that the dogs fit into. The are other designs as well. When you shift since there is no synchro to make the gear speeds match you have to match revs with a blip of the throttle for a smooth shift. But that's not necessarily accurate, really, because you can crash it right in. That's why they are also known as "crashboxes". The clutch is not required when shifting. When accelerating a quick, partial lift of the throttle will do. When downshifting a blip of the throttle to match revs will ensure a smooth shift. A dogbox will shift as fast as you can move the gear lever! No waiting for synchros. Also, the dog mechanisms don't take up as much room as synchros so a wider gear can be fitted.


Q: Can you use a WRX transmission in an RS and vice versa?
A: The RS transmission bell housing is totally different from the WRX. Prop shaft and half shafts are the same between both except the WRX sedan because of wider track. In addition, the WRX runs a 3.90 differential in the front versus the 4.11 for the RS.


Q: Where is the fuel filter?
A: It is located on the driver side front strut tower in the engine bay. It is a small silver or black cannister with several black fuel lines running into it.


Q: What's the difference between turbo back and cat back?
A: A cat-back exhaust system replaces everything from the rear catalytic convertor out to the tailpipe (ie: the midpipe and the exhaust cannister). A turbo-back exhaust would replace everything from the outlet side of the turbo to the tailpipe (ie: the downpipe, midpipe, and cannister).


Q: Whats the torque spec for my spark plugs?
A: Approximately 15 ft-lbs of torque.


Q: When is the best time to switch to synthetic motor oil?
A: The general rule of thumb has been to allow the engine to break in for five to ten thousand miles on "dino" oil before switching to synthetic, to allow the seals to expand. No real evidence of long-term problems has arise from switching from much earlier however, including going to synthetics from day one.


Q: What is an Up-pipe, Down-pipe, and/or Mid-pipe?
A: An Up pipe is the pipe that leads from the exhaust header collector up to the turbocharger. A down pipe leads from the exhaust side of the turbocharger down to meet the midpipe of the exhaust. The Midpipe is the center pipe leading from the catalytic convertor or downpipe to the exhaust cannister.


Q: How do you reset the ECU?
A: There are two methods to achieve this:

Method One
With the engine at operating temperature, turn the engine off. Place gear shift lever into park (auto transmission) or out of gear (manual transmission). Locate the two ECU check connectors, for most cars they are located under the steering column and consist of a black plastic male and female connector, and a green male female connector. The exact location of the connectors varies with the different year models, but generally they are located under the steering column on the drivers side (note: sometimes they are still taped over with some small amount of plastic tape). With the ignition OFF connect black to black and green to green. Turn on ignition, do not start the engine, (and for auto transmission, cycle the gearshift lever from park to neutral and back to park ), depress the accelerator pedal to full throttle and hold for a few seconds, and then release. Start engine and then drive for at least one minute, keeping road speed above 10mph. ECU is now re-set. At this point the check engine light should start to flash the all clear signal (steady 1/2 second interval flashes). If the check engine light does not flash, or indicates some other sequence, there is a fault present in the system, and should be professionally checked for necessary repairs. Stop the car, turn off the engine, and disconnect the plugs.

Method Two
According to conventional wisdom, you need to disconnect the battery for at least 30 minutes. Reconnect the battery after this time, and then idle the car until the cooling fan cycles at least once to reset the timing maps (approximately 10 minutes). Drive the car as usual.


Q: Where is the ECU?
A: It is under the passenger side foot well. Pull back the carpet and remove the metal plate any you will see it.


Q: Should I replace the crush washer every oil change?
A: Yes. The washer is meant to form a seal between the pan and the oil drain nut, so that you do not have to overtorque the nut to prevent leaks. They cost very little, and should be changed with every oil change.


Q: Whats the K&N Filter Part # for the WRX or RS?
A: RS: 33-2154, WRX: 33-2031-2

LIGHTING

Q: Why won't my parking lights shut off?
A: That switch is known as the "parking light switch". One of the greatest Subaru features requires that switch. When you turn the car off, the lights go off too. In order to be legal in some countries - you must be able to put the parking lights on (while parked - imagine that). The switch is there so you don't have to leave the car running.


Q: Why shouldn't I use high-wattage headlamp/foglamp bulbs?
A: In the stock headlamps, the reflectors are chromed plastic, and they are not capable of handling the large amounts of heat created by higher wattage bulbs. In addition, the stock wiring is not up to the task of handling the current draw created by higher wattage bulbs. Upgrading the wiring harness and/or the headlamps themselves enables you to run higher wattage bulbs safely.


Q: What are the size of the stock headlamp/foglamp bulbs?
A: RS Headlamp- H4, Foglamp- H3; WRX Headlamp- 9007, Foglamp H3

SUSPENSION, BRAKES, RIMS, AND TIRES

Q: What is understeer?
A: Understeer is when the car plows into a corner. The wheels are turned, yet the car is still going straight.


Q: What is oversteer?
A: Oversteer is when the rear of the car swings outward towards the corner. This is also known as "tail out" and "fish tailing".


Q: What are coilovers?
A: Coilovers are an adjustable spring (or coil) mounted over the dampener. Using a threaded collar - you can adjust the springs up or down on the strut. Raising or lowering the car, and changing the dampening effect.


Q: What is camber?
A: Camber is the angle of the wheels from top to bottom. The more negative camber - the more the top of the wheel is pointed towards the car. A degree or two of negative camber is good for hard turns as the outside wheel is angled to take the force of the corner and keep the car planted in the turn.


Q: What is toe?
A: Toe is the left right angle of the wheels. Sometimes the rear wheels of other cars are placed "toe in" to make the car more stable at high speeds. Where the left wheel is turned right a degree, and the right wheel is turned left a degree.


Q: What are camber plates?
A: Camber plates sit at the top of the strut, and allow the strut to be adjusted in several directions. Changing the attitude of the wheels. You will also see the term pillowball mounts used when discussing camber plates.


Q: What are pillowball mounts?
A: A pillowball mount is basically a ball bearing mounted in stiff rubber - or similar material. These sit on top of your struts, and allow the wheels, struts, and springs to turn when you steer the car.

The offset can be one of three types:
Zero Offset
The hub mounting surface is even with the centerline of the wheel.


Positive
The hub mounting surface is toward the front or wheel side of the wheel. Positive offset wheels are generally found on front wheel drive cars and newer rear drive cars.


Negative
The hub mounting surface is toward the back or brake side of the wheels centerline. "Deep dish" wheels are typically a negative offset.
If the offset of the wheel is not correct for the car, the handling can be adversely affected. When the width of the wheel changes, the offset also changes.


Q: Whats the right offset for wheels for my car?
A: The recommended offset for most Subarus is +53mm in a 7" wide wheel. The correct offset is dependent upon the width of the wheel (ie: a +48 offset is acceptable for a 7.5" or 8" wide rim).


Q: Can I use wheel spacers to get the proper offset?
A: Wheel spacers have the opposite effect you are looking for- to get a +50mm offset to a +55mm, you need to remove material. Adding a 5mm spacer to a +50 offset nets you a +45 offset.


Q: What do stainless steel brake lines do and are they worth getting?
A: Stainless steel lines simply do not expand like the stock rubber hoses under extreme pressure when you press your brak pedal. When the rubber hose expands, you waste some of the pressure in your braking system and therefore loose some brake system performance.


Q: What are the torque specifications for wheel lug nuts?
A: Lug nuts should be torqued down to between 58 and 72 ft-lbs.

Information created by unabomber of www.nasioc.com

Blow Off Valve FAQ

Term usage: "Blow off valves" go by several names, among them are compressor bypass valve (CBV), air by-pass valve, bypass valve (BPV), blow off valve (BOV), Diverter valve, and possibly a few others. BOV is the common and incorrect term that lumps true blow off valves and bypass valves under the same term. For the sake of correctness, this post will refer to either aftermarket BOV, aftermarket BPV or OEM BPV as these are the most correct terms.

What is the function of a blow off valve (BOV)? To release pressure from the intake tract of a turbo car when the throttle closes. It is a vacuum-actuated valve designed to releases the air to the atmosphere.

What is the function of a bypass valve (BPV)? To release pressure from the intake tract of a turbo car when the throttle closes. It is a vacuum-actuated valve designed to recirculate the air back into the intake before the turbo inlet, but after the airflow sensor.

What is the purpose of a BOV/BPV? When the throttle closes and the intake system is under pressure, the high-pressure air entering the motor will bump into the closed throttle plate, and in the absence of a BOV/BPV, a pressure wave will travel back to the turbocharger. The result is that the compressor wheel will stall (a phenomenon known as “compressor surge”) and slow down very quickly. This is hard on the bearings and decreases the turbo’s lifespan, but it also means the turbo will take longer to spin up the next time the throttle is opened.

Are aftermarket BOVs necessary with Subaru turbos? No. The OEM BPV is perfectly fine up to 20psi of boost. For applications using higher boost levels, an aftermarket BOV/BPV should be considered.

Can I mod my stock BPV to hold higher boost? Yes. This link gives detailed instructions on how to do so.

Is the STi BPV better than the WRX BPV? No. They are the same. However, the JDM STi BPV will hold more boost as it is physically different than both the USDM STi BPV and the WRX BPV. The specific PSI rating of the JDM STi BPV is unknown.

Which manufacturer is best? This topic is highly debated. There have been no reported consistent "bad" aftermarket Bovs. Obviously, there may have been bad ones sold, but not enough to report as "bad" overall.

What are the different types of aftermarket BOVs/BPVs? Different manufacturers use different methods. There are three basic types:
1. Aftermarket BPV: Similar in function to the OEM BPV where 100% of the air is recirculated.
2. Atmospheric BOV: 100% of the air is vented to the atmosphere.
3. Hybrid BOV: These depend on the manufacturer and end user settings. These can either be adjustable or manufacturer set for different percentages of atmospheric/recirculation dumping. They can also be set to work as recirculation during lower boost conditions and 100% atmospheric during higher boost conditions.

Are there any downsides to aftermarket BOVs? There have not been significant amounts of problems with BOVs. Aftermarket BOVs can and do require some light end user maintenance to keep them performing perfectly. For aftermarket hybrid BOVs that have end user defined settings, there will be an initial period of adjustment to obtain the desired recirculation/atmospheric ratio. As well, most aftermarket BOVs will require "tuning" (usually via supplied washers, a screw, or other mechanism on the BOV itself) to allow them to idle correctly and blow off at the right time.

Are there any negative effects with aftermarket BOVs? Yes. The downside of releasing the air to atmosphere is that it has already been metered by the mass air sensor, and when it blows off, the ECU will be injecting the wrong amount of fuel into the cylinders. The engine temporarily runs extremely rich, meaning too much fuel is injected into the cylinders.

This temporary rich condition isn’t usually that harmful, but it can cause bucking or hesitation on lift-throttle. If the condition is really bad, it can eventually foul spark plugs and even clog the catalytic converter as unburned fuel on the catalytic converter burns very hot, and too much of it can melt the cat.

Can my tuner or engine management tune out this rich period? No.

Where do I buy aftermarket BOVs/BPVs? Every Subaru/Import performance store sells BOVs. For purchasing, support your local economy or the NASIOC Vendors.

How hard is it to install aftermarket BOVs/BPVs? Allow around 1 hour for install time. Professional installation, depending on your area, is around $75. This is one vehicle modification that is very simple and can be successfully accomplished by even the greenest shade tree mechanic.

How do I install BOVs/BPVs? Refer to the BOV/BPV manufacturer's instructions. For BOVs/BPVs without instructions, below is a link to one of the better known installation instructions:
scoobymods.com instructions (with photos)

Downpipe FAQ

The primary purpose of an aftermarket downpipe is to remove or replace the stock catalytic converter with a better flowing unit. It also increases the exhaust diameter for better flow.

HP gain is 15-20HP. This figure is highly debated as different manufacturers use different dynos with different cars with different levels of mods. It also varies because some downpipes use one high flow cat, while others are catless and actually extend far enough back to eliminate the 3rd cat as well.

Which manufacturer is best? This topic is highly debated. There have been no reported consistent "bad" downpipes on the market. Obviously, there may have been bad pipes sold, but not enough to report as "bad" overall.

Who manufactures downpipes? The NASIOC user fliz has kindly started a downpipe chart that lists all the downpipe manufacturers and lots of comparative data. fliz's downpipe chart.

What downpipe metal material is best? Downpipes are made from mild steel and stainless steel (304 & 321). There is no irrefutable evidence that one material is better than the other. Obviously, corrosion levels are higher with mild steel (coated or otherwise). Article on exhaust materials.

Which downpipe construction method is best? Downpipes have 4 main construction methods:
1. Blank plate: Identical to stock construction with the wastegate portion completely covered.
2. Bellmouth: Completely open design.
3. Split bellmouth: Similar to bellmouth only with a divider inserted to separate the wastegate.
4. Divorced or Twin Dump: Separate exhaust and wastegate piping that connect further downstream.

There is no irrefutable evidence that one design is better than the other. The thought process is that the greater the separation there is between the wastegate gases and exhaust gases, the smoother the overall exhaust flow.

http://www.wallpaperinstaller.com/scooby/downpipe.jpg

Which downpipe construction method is least expensive? Generally, the blank plate design is the least expensive. The other designs, depending on manufacturer, are all around the same general price range.

Can I gut my downpipe like people do their uppipe? Yes. Scoobymods.com directions. Others have used a 2 foot section of bent rebar and a hammer and reported the de-catting process takes 30 minutes total if the scoobymods directions seem too labor intensive.

Can I use an STi downpipe? Yes. There is very little difference between the STi and WRX downpipes though. Using the STi downpipe is fine, but do not consider it a significant upgrade. Differences in HP between the two are likely to be very tiny (5HP or less is a guess) and not worthwhile.

What other differences are there with downpipes? The other differences are as follows:
1. High flow cat or catless.
2. Overall pipe diameter. Sizes range from 2.5, 3.0, and 3.5 inches. 3.0 and 3.5 are generally only necessary for higher (300-400+ HP) applications.
3. Length of downpipe, some are stock length and others are longer to remove the 3rd cat.

Which downpipe has the best gains? There is no irrefutable evidence that any downpipe has better gains than another. The consensus, if there is one, is they are all within 5HP or less, gain wise, of each other.

Are there any downsides to downpipes? There have not been significant amounts of problems with downpipes. There have been some reports of wastegate issues with split bellmouth and divorced or twin dump downpipes. These type of downpipes have a "splitter piece" that juts into the turbo to separate the exhaust from the wastegate. Sometimes this piece is too long and requires some slight cutting or grinding for a perfect fit. The telltale sign of this occurance is less than full boost or irratic boost upon installation. As with any aftermarket part, even "perfect" ones, sometimes you run into a rogue issue. From research, this is not a widespread issue at all, only an advisory if this situation should occur.

Where do I buy a downpipe? Every Subaru/Import performance store sells downpipes. For purchasing, support your local economy or the NASIOC Vendors.

What is some good background information about exhaust pipe fitment?
Generally speaking, there are two types of catbacks:
Type 1: It has a sliding flange designed to bolt up to the stock downpipe.
Type 2: It has a flat flange designed to bolt up to 3" downpipes.

Generally speaking, there are two types of downpipes:
Type 1: It is designed to bolt up to the stock catback and other type 1 catbacks.
Type 2: It is designed to bolt up to only type 2 downpipes.

Type 1 catbacks do not bolt up well to type 2 downpipes, and type 2 catbacks do not bolt up well to type 1 downpipes.
Type 1 catbacks and downpipes taper to 2.5" where they meet.
Type 2 catbacks and downpipes are full 3".
Type 2 downpipes are usually less expensive than type 1 downpipes.
Type 1 and 2 catbacks are relatively similar in price.

All 2.5" catbacks are type 1.
Some 3" catbacks are type 1, and some are type 2.

What questions should I ask of the retailer or manufacturer before purchasing?
1. Will this unit mate up to the rest of my exhaust? Some downpipes will fit the stock exhaust, or must be fitted to a larger exhaust.
2. Will this unit throw a CEL? Some do, some don't, so find out beforehand.
3. Does it come with new gaskets? It is always a good idea to replace exhaust gaskets.
4. Does it come with a CEL fix if needed and is it the right one? In the case of the electrical fix, there are two unique fixes, one for the 02/03 and one for the 04. The 05+ does not currently have an electrical fix.

How hard is it to install a downpipe? Allow around one-two hours for install time. Professional installation, depending on your area, is around $75. This is one vehicle modification that is very simple and can be successfully accomplished by even the greenest shade tree mechanic.

How do I install a downpipe? Refer to the downpipe manufacturer's instructions. For downpipes without instructions, below are links to some of the better known downpipe installation instructions:
TurboXS's Instructions
Perrin's instructions
Scoobymods.com instructions

What about ceramic or other heat wrap coating?
Pros:
Increased heat retention, which is beneficial for exhaust flow.
Reduces underhood temps, which decreases IC heatsoak.
Cons:
Additional expense.
Additional lead time, in the case of coatings.
Increased heat retention, which accelerates metal fatigue, especially at weld joints.
No proven HP increase.
If you plan on using a coating, ensure you are aware of what impact this will have on your downpipe warranty if applicable. Coating or wrapping your downpipe can void exhaust component warranties.

What types of ceramic or other heat wrap coating are available? The two most popular manufacturers of heat wrap are Thermo Tec and DEi. The two most popular coating manufacturers are Jet Hot and Swain Tech Coatings. Wrapping is a DIY project with a shorter life span than the professional only coating with a longer life span.

.pdf file on coatings
Car Craft magazine's testing of Jet Hot

What is the CEL fix? It stops the rear CEL code P0420 Catalyst System Efficiency Below Threshold from appearing, this code being caused by the lack of a catalytic converter in the downpipe. This is usually fixed with a Pony Express MIL Eliminator or similar fix. Ensure you obtain the correct type for your model year as there are two types: 02/03 and 04. The 05+ does not currently have an electrical fix. Another fix is the mechanical fix, which works on all models. ***NOTE*** There are two CEL fixes for the WRX, the other one is the 2.2 KOhm 1/2 watt resistor. It is used to combat the CEL code P0546 = Exhaust Gas Temperature Sensor Circuit Malfunction (High Input) in the uppipe. This notice, though not important to this thread, acknowledges there are two "CEL fixes" and defines them individually to avoid possible confusion.

Which is the best CEL fix, mechanical or electrical? Both work fine, though personnel living in states with OBDII testing prefer the mechanical fix. The reason for this is during state mandated OBDII testing, the electrical fix can show up as a malfunctioning sensor. For some states, this one malfunctioning sensor is fine, for others, you will have to fix it and return. In the end, the mechanical fix is cheaper and easier for most users.

Should I reset my ECU after this mod? It is never a bad idea to perform an ECU reset after a mod. The traditional route is to disconnect the negative battery terminal, press the brake pedal for a few seconds to bleed the system of charge, and reattach. Some use the more advanced Vishnu Reset.

What about emissions problems like emissions tests and legality? Using a catless downpipe is a violation of section 203 of the Clean Air Act. Each state has statutes that cover this subject as well. As far as passing state emissions tests, as long as you still have one cat in your system, you should be fine unless you run into a sharp-eyed and knowledgeable inspector who knows there should be two in the main exhaust. The exhaust should be properly warmed prior to any testing to ensure it is operating efficiently. Another smart move is to find someone in your local area with the same set up to compare notes.

Engine Management FAQ

Why do I need engine management? Consider your stock engine management for just a moment. Your stock engine control unit (ECU) is a very complex piece of circuitry that calculates hundreds of variables every second. All of these variables rely on inputs within a + or – range. When you modify your vehicle, these values change. As long as the changes are within the values the ECU expects to receive, your engine runs fine. Once the values are exceeded, the ECU is programmed to compensate to return the values to normal levels.

This is a layman’s explanation of how your stock ECU can actually work against you when modifying your vehicle. This also explains why modifications can feel great once they are bolted on but the butt dyno results seem to fade over time. This is due to ECU compensation.

What will engine management do for me? Generally speaking, engine management optimizes several engine functions to create more horsepower and efficiency. The stock ECU is designed to ensure your car runs fine and monitors the engine’s output parameters. Utilizing an aftermarket engine management solution takes this to the next level.

Often times, car manufacturers will program the stock ECU with a known amount of “play”. This amount of play allows the manufacturer an extra level of safety and/or the ability to utilize this at a later date so they can have an increase in HP in later years. An example of this is where a 2001 car has 200HP and a 2002 car has 215HP. Some manufacturers couple this with additional parts to get increased HP levels, but this should give you some idea of the concept. From a marketing and sales aspect, this ensures that the public will continually be interested in the new year models, even if the body style does not change. While this FAQ is not about the science and art of auto sales, this may give you an insight as to why the stock ECU is not 100% perfectly tuned from the factory.

What are the least talked about benefits of engine management? Engine management solutions to one degree or another can reduce or eliminate black tailpipes, improve driveability throughout the powerband, eliminate the open/closed loop delay in 04+ Subarus, and increase MPG.

What about manual/electronic boost controllers or air fuel controllers?
A manual/electronic boost controller or air fuel controller really isn't engine management. MBCs are fine when used correctly on 02/03 by a judicious user. The issue gets further clouded on 04+ due to the open/closed loop delay. One can lump in the mix air/fuel controllers as well for the same reason. Usually those two devices are used by either cheap skates, n00bs, or advanced users who combine them with other forms of real engine management.

What types of engine management solutions are available? They fall into one of these general categories:
a. Reflashed ECU
b. Custom Tuned ECU
c. Piggyback Engine Management
d. Stand Alone Engine Management

Reflashed off the shelf ECU: This is your stock ECU that has had the programming modified. This form of engine management is best suited for people who:
a. Have a “set it and forget it” attitude towards engine management
b. Live in remote areas and do not have easy access to a tuner
c. Do not want to learn or are uneasy doing their own tuning
d. Want to modify their vehicle to a certain level and quit or add parts very infrequently

It is important to note that while reflashed ECUs are considered a static engine management option, they can be custom tuned by the end user by utilizing additional add-ons from the manufacturer or via a custom tuned reflash by an authorized tuner.

In addition, also consider that EcuTek tuners might have reflashes for your exact equipment set-up based on their prior custom tunes. This means that someone who has a full TBE might find the Cobb AccessPort a better plug and play solution, while someone with a full TBE, uppipe, headers, & a lightweight pulley may find an EcuTek reflash a better plug and play solution if they can find an EcuTek tuner with that exact map.

Examples of reflashed ECUs are the Cobb AccessPort and EcuTek (including Prodrive’s PPP & Vishnu’s reflash).

Reflashed custom tuned ECU: This is the next evolution to a reflashed ECU. This allows either the end user or a professional tuner to custom tune your vehicle to your specific modifications, wants and desires, type of gasoline used, and geographic area. This form of engine management is best suited for people who:
a. Will probably modify their vehicle frequently and require additional tuning
b. People with the ability to do their own tuning
c. People that live close to a tuner
d. People that want to get the maximum power and safety out of their car

Examples of Custom Tuned ECUs are Cobb Tuning’s StreetTUNER for end user tuning, Cobb Tuning’s ProTuner for professional custom tunes, EcuTek custom tune via an EcuTek tuner. EcuTek will shortly be releasing, DeltaDash Live User Tuning, an end user tuning solution.

Piggyback Engine Management: This is an engine management option that works in conjunction with your stock ECU. Depending on the manufacturer, this solution works by the piggyback unit controlling some engine management functions and the stock ECU controlling others. This form of engine management is best suited for people who:
a. Will probably modify their vehicle frequently and require additional tuning
b. People with the ability to do their own tuning
c. People that live close to a tuner
d. People that want to get the maximum power and safety out of their car

It is important to mention that most piggyback units come with base maps. These base maps work very similar in function to a reflashed ECU whereas you can run the base map and be 100% fine, or when the day comes for someone to tune their own car or have it professionally tuned, they may do so.

Examples of Piggyback Engine Management are Unichip, Xede, UTEC, and others.

Stand Alone Engine Management: This is an engine management solution that totally replaces the stock ECU and controls 100% of the engine’s functions. This form of engine management is best suited for people who:
a. Will probably modify their vehicle frequently and require additional tuning
b. People with the ability to do their own tuning
c. People that live close to a tuner
d. People that want to get the maximum power and safety out of their car

This form of engine management is generally reserved for more advanced users and people going for really high levels of performance.

It is important to mention that most stand alone systems do come with base maps. Unlike the base maps that come on reflashed ECUs, these base maps are meant for your vehicle to run for a short period of time and are not meant to be used as a permanent solution as is the case with the other base maps as described above. Consider these base maps as merely as short term option until end user or a professional tuning.

Examples of stand alone engine management are MoTeC, Hydra, AEM, and others.

Can the dealer detect my reflashed ECU (AccessPort/EcuTek)?

YES the checksum of the ECU changes.
YES the dealer can easily read the checksum.

NO the dealer has nothing to compare the checksum against there are many revisions of the WRX ecu they all have different checksums. If the dealer had someway of putting this checksum into a database he COULD verify that the code had been modified but at this time he doesn't.

The 05+ ECU and some of the 04s have the VIN in the ECU code. The current versions of reflashed ECUs only change the tables so the VIN will report when queried.

Bottom line: If you don't want modifications to be detected, don't modify the car.

What are some specific types of engine management While this FAQ does not go into specifics for every type of engine management, this thread covers many types. This link offers several comparisons of different system features as well. There are some not covered in these threads though and may be considered as well.

Generally speaking, what engine management option will give me the most power? Custom tuned engine management solutions will always give you more power. Every off the shelf engine management solution has a built in safety factor. This depends on the manufacturer. This is because their “Stage 1” or “VF-30” map has to safely make power for someone living in Phoenix’s heat and 91 octane, to Denver’s high altitude, to Boston’s cold and 93 octane. The gasoline and geographic variances can leave horsepower on the table.

More specifically, what engine management option will give me the most power? This is one question without a correct answer. Let’s say that you research a very comprehensive stand alone engine management system such as a MoTeC unit and decide that it’s the “best” for your car. At the end of the day, it’s about what the tuner is most comfortable with. Some tuners may be able to extract better results from a “lesser” system simply because they understand the interface better.

For someone interested in tuning their own vehicle, they should match their tuning skills with an engine management solution that they are able to understand and use correctly. For someone interested in professional tuning, they should consult with their tuner for their recommendations. Both of these actions will ensure a good tune with a minimum amount of rework, guessing, and trial and error. While most tuners are capable of learning new or more advanced engine management systems, consider the benefits of an “older/worse system” your tuner is familiar with vs. your tuner learning a “newer/better system” at $200/hour plus possible dyno time.

I have a reflashed ECU and am not seeing their advertised HP, why? First off, have you met their criteria EXACTLY? The #1 cause of low HP with reflashed ECU owners is their lack of meeting the manufacturer’s requirements. If they require a full turbo back exhaust and you only have a downpipe and a cat back exhaust, 100% of the blame is on the end user. As well, if they require a full exhaust and you have a full exhaust, uppipe, headers, and a bigger top mount intercooler, this can cause problems as well.

Also realize that HP figures vary. You cannot compare (for example) a manufacturer’s Mustang Dyno HP figures to your local DynoJet HP figures. Even comparing identical dynos to each other is futile as dyno software set-up, altitude, temperature, humidity, and other factors do not ensure an equal result.

In addition, realize that a reflashed ECU still utilizes many of the stock ECU’s learning functions. This means that in a perfect world, you will see the advertised HP from your reflashed ECU. This may also mean that on the day of dyno testing, your octane, the temperature, humidity, and many other factors are considered by the reflashed ECU when determining total power output. If the advertised numbers aren't there on dyno day, it doesn’t necessarily mean there is a problem, but rather, your ECU is protecting your engine from low octane, high temperature, high humidity, or other factors.

How much is a custom tune by a professional? Expect to pay $100-$150 per hour for the dyno time. Your tuner’s fee depends on their level of experience and pricing. Tuners generally charge $100-200 per hour for their time. The amount of total tuning time depends on the tuner and the amount of time you wish for them to tune your vehicle. Most tuners can get your vehicle within 90-95% of its maximum power within 1-2 hours.

What are some helpful tools to use if I want to monitor my engine’s functions? Some engine management solutions come bundled with engine monitoring software, which is an excellent way to see hard data on your tuning results. If this software does not come bundled with your engine management, consider one of the following solutions:
Simple data logger
TARI DL1 (Diagnostics Level 1) Data Logger
DeltaDash
LogMapper
MPS UTECLogger
Auto-Logger
Scanmaster 3

What gauges/tools are important if I wish to tune my own vehicle? These are considered the "must have" tuning items:

a. Wideband O2 sensor/gauge
b. EGT gauge
c. Boost gauge

What are some other useful tuning tools?
a. Knock detection hardware
b. SMC 4 channel EGT

Exhaust FAQ

The primary purpose of an aftermarket exhaust is to remove or replace the stock catalytic converter(s) with a better flowing unit. It also increases the exhaust diameter for better flow. The term "aftermarket exhaust" can be broken down into the three main types:

1. Turbo back exhaust (TBE) covers items 1-4 as described below.
2. Cat back exhaust (CBE) covers items 3&4 as described below.
3. Axle back exhaust (ABE) covers item 4 as described below.

The stock Subaru exhaust consists of:

1. Downpipe (with cat) | 2. Midpipe (with cat) | 3. Rear Exhaust Pipe | 4. Axle Back Muffler

IMAGE

HP gain is dependent on the type of exhaust chosen. TBE gains are 20-30HP. CBE gains are 5-15HP. ABE gains are 5-10HP. These figures are highly debated as different manufacturers use different dynos with different cars with different levels of mods. It also varies because exhausts use different amounts of catalytic converters or are catless.

How do I stop my car from sounding like a "Honda Killer Bee Exhaust"? Subaru boxer configured engines, even equipped with a "Honda Killer Bee Exhaust" will NOT sound like a buzzy, annoying exhaust due to the motor's natural sound. The only way to become buzzy is to switch to an equal length header. The OEM exhaust manifold and aftermarket unequal length manifolds (headers) retain the exhaust pulses at different intervals which create the unique boxer sound. This is why your stock exhaust sounds similar to a VW Bug or Porsche engine.

Which manufacturer is best? This topic is highly debated. There have been no reported consistent "bad" exhausts on the market. Obviously, there may have been bad exhausts sold, but not enough to report as "bad" overall.

What exhaust metal material is best? Exhausts are made from mild steel, stainless steel (304 & 321), and titanium. There is no irrefutable evidence that one material is better than the other. Obviously, corrosion levels are higher with mild steel (coated or otherwise). Article on exhaust materials.

Which exhaust diameter is best? Exhausts have 3 diameters:

1. 2.5": Good for 300-350 HP
2. 3.0": Good for 500-600 HP
3. 3.5": Good for 600HP +

There is no irrefutable evidence that one diameter is better than the other. Purchasing a larger exhaust than needed for your level of modification has no advantages or disadvantages. Naturally aspired vehicles, as they respond better to backpressure, should always choose an exhaust catered towards their specific needs.

What other differences are there with exhausts? The other differences are as follows:
1. High flow cat(s) or catless.
2. Exhaust pipe length. Some manufacturers have proprietary exhaust component lengths. This means you have to use all of their exhaust piping or some of it with a custom piece. As well, JDM specification exhuasts are different lengths and require all JDM specification piping or some of it with a custom piece. Additionally, some manufacturer's components may take the place of two OEM components. This generally occurs with the downpipe section of a TBE where the "downpipe" is actually a downpipe/midpipe.

Which exhaust has the best sound? This subject is up to the individual. It is highly subjective and can lead to trouble with local noise abatement ordinances. That great sounding exhaust may be the cause of some expensive and/or time consuming noise abatement tickets. Arguably, the three most famous/popular "best" sounding exhausts are the ScoobySport, Stromung, and Prodrive. A smart move is to find someone in your local area with the exhaust component(s) you are interested in to hear it in person. Seek out locals via the NASIOC Chapters or NASIOC Regional Areas.

Which exhaust is the quietest? This question can be answered by listing hard data:

a. M2 Performance 94dB @ idle
b. GReddy Evolution 94dB @ idle
c. MRT Twin Tip: 96dB @ idle
d. Prodrive: 91dB @ idle
e. STi Muffler: 93dB @ idle

By using hard data, you remove human judgement and don't get stuck with a recommend "quiet exhaust" that in your opinion is now a loud and expensive nuisance. Keep in mind that these quiet exhausts only protect you from the chance encounter in areas with strict noise abatement laws. At wide open throttle (WOT) any aftermarket exhaust is considerably louder than OEM and even the quiet ones will not protect you from folly.

Additional full dB testing data can be found on this link.

Which exhaust is the loudest? "Commonly known" loud exhausts are the TurboXS RFL, Worx Tuning, Helix, Blitz NUR Spec R, Kakimoto, and BPM Twister MKIII.

Additional full dB testing data can be found on this link.

How do I quiet down an already loud exhaust?
1. Install an aftermarket silencer. This is an insert that is fitted into your tailpipe.
2. Install a resonated exhaust tip.
3. Have an inline resonator welded into your exhaust.
4. Install an auger style muffler.

One special note about silencers. While they do quiet down your exhaust, they generally work by restricting your exhaust flow down to a 1 1/2" hole. Strongly consider what this does to your backpressure and the effects of backpressure on a turbocharged engine.

Which exhaust has the best gains? There has not been a 100% conclusive test of every aftermarket exhaust to prove or disprove best gain level.

Are there any downsides to exhausts? There have not been significant amounts of problems with exhausts. For STi owners, there have been reports of overboosting issues with some TBEs. For more information read this post and the follow on posts it contains.

Where do I buy an exhaust? Every Subaru/Import performance store sells exhausts. For purchasing, support your local economy or the NASIOC Vendors.

What should I decide upon before purchasing to narrow down my decision?
a. Sound level.
b. Exhaust tip(s) diameter and shape.
c. Catalytic converter issues with regard to your particular state's emissions laws.
d. Outside appearance, straight back exhaust or angled exhaust?

What questions should I ask of the retailer or manufacturer before purchasing?
1. Will this unit mate up to the rest of my exhaust? Some exhausts will fit the stock exhaust, or must be fitted to a larger exhaust.
2. Will this unit throw a CEL? Some do, some don't, so find out beforehand.
3. Does it come with new gaskets? It is always a good idea to replace exhaust gaskets.
4. Does it come with a CEL fix if needed and is it the right one? There are two unique fixes, one for the 02/03 and one for the 04. The 05+ does not currently have an electrical fix.
5. Will this exhaust clear the rear differential protector, if applicable?
6. Does this exhaust drone? Drone is a term to describe an annoying monotonous buzzing sound generally heard during long highway trips. This sound can be more apparent with wagons, due to the lack of a trunk to deaden the sound.
7. Special note to STi owners: Most WRX exhaust will fit the STi, but it is recommended you check with your Vendor/seller prior to purchasing as there are a few exhausts that have STi fitment issues.

If after installation, my exhaust drones, how do I fix it? Many users report great success by using audio sound deadening material in the trunk, back seat area, and/or underneath your vehicle.

What is some good background information about exhaust pipe fitment?
Generally speaking, there are two types of catbacks:
Type 1: It has a sliding flange designed to bolt up to the stock downpipe.
Type 2: It has a flat flange designed to bolt up to 3" downpipes.

Generally speaking, there are two types of downpipes:
Type 1: It is designed to bolt up to the stock catback and other type 1 catbacks.
Type 2: It is designed to bolt up to only type 2 downpipes.

Type 1 catbacks do not bolt up well to type 2 downpipes, and type 2 catbacks do not bolt up well to type 1 downpipes.
Type 1 catbacks and downpipes taper to 2.5" where they meet.
Type 2 catbacks and downpipes are full 3".
Type 2 downpipes are usually less expensive than type 1 downpipes.
Type 1 and 2 catbacks are relatively similar in price.

All 2.5" catbacks are type 1.
Some 3" catbacks are type 1, and some are type 2.

How hard is it to install an exhaust? Allow around one hour for install time. Professional installation, depending on your area, is around $75. This is one vehicle modification that is very simple and can be successfully accomplished by even the greenest shade tree mechanic.

How do I install an exhaust? Refer to the exhaust manufacturer's instructions. For exhausts without instructions, below is a link to one of the better known exhaust installation instructions:
TurboXS's Instructions

Do I need aftermarket exhaust hangers? This can depend on many factors and the only clear indication is during the post installation driving test. Some exhausts work perfectly fine with the OEM hangers and some can benefit from the added stiffness or extended length of the aftermarket hangers provide. They are fairly inexpensive and can be good insurance for a perfect, rattle free exhaust install.

What about ceramic or other heat wrap coating?
Pros:
Increased heat retention, which is beneficial for exhaust flow.
Reduces underhood temps, which decreases IC heatsoak.
Cons:
Additional expense.
Additional lead time, in the case of coatings.
Increased heat retention, which accelerates metal fatigue, especially at weld joints.
No proven HP increase.
If you plan on using a coating, ensure you are aware of what impact this will have on your exhaust warranty if applicable. Coating or wrapping your exhaust can void exhaust component warranties.

What types of ceramic or other heat wrap coating are available? The two most popular manufacturers of heat wrap are Thermo Tec and DEi. The two most popular coating manufacturers are Jet Hot and Swain Tech Coatings. Wrapping is a DIY project with a shorter life span than the professional only coating with a longer life span.

.pdf file on coatings
Car Craft magazine's testing of Jet Hot

What is the CEL fix? It stops the rear CEL code P0420 Catalyst System Efficiency Below Threshold from appearing, this code being caused by the lack of a catalytic converter in the exhaust. This is usually fixed with a Pony Express MIL Eliminator or similar fix. Ensure you obtain the correct type for your model year as there are two types: 02/03 and 04. The 05+ does not currently have an electrical fix. Another fix is the mechanical fix, which works on all models. ***NOTE*** There are two CEL fixes for the WRX, the other one is the 2.2 KOhm 1/2 watt resistor. It is used to combat the CEL code P0546 = Exhaust Gas Temperature Sensor Circuit Malfunction (High Input) in the uppipe. This notice, though not important to this thread, acknowledges there are two "CEL fixes" and defines them individually to avoid possible confusion.

Which is the best CEL fix, mechanical or electrical? Both work fine, though personnel living in states with OBDII testing prefer the mechanical fix. The reason for this is during state mandated OBDII testing, the electrical fix can show up as a malfunctioning sensor. For some states, this one malfunctioning sensor is fine, for others, you will have to fix it and return. In the end, the mechanical fix is cheaper and easier for most users. (Most subaru places in Calgary will do this for you , its much better to go this route.)

The primary purpose of an aftermarket turbo is to increase the performance over the stock unit. This can be accomplished by choosing a turbo with better spool, more flow, or a combination suited to the end user's needs.

What is some good background turbo information?

howstuffworks.com's turbo walkthrough

Common Terms:
Boost threshold- the lowest RPM at which a turbo will generate positive manifold pressure at maximum engine load.
Turbo lag- the time between hitting the throttle and the turbo providing full boost.

Recommended Reading:
Maximum Boost by Corky Bell is considered by many to be THE publication for turbocharger information.

What is the best turbo? There is no best turbo. Generally speaking, aftermarket turbos fall into these generic categories:
a. Turbos with a little more top end power
b. Turbos with a lot more top end power
c. Quicker spooling turbos

What do all the names and numbers of turbos mean? This link sorts many of them out nicely.

What supporting upgrades are required for aftermarket turbos? At a minimum, aftermarket turbos require a fuel pump, injectors, and engine management for safe operation.

Is there a turbo upgrade that does not require other upgrades? Yes. A ported and polished (P&P) stock turbo is an easy upgrade over the stock unit. Though there are many turbos that may be used for short periods of time with a boost controller, it is generally unwise to bolt on an aftermarket turbo with a boost controller.

What is the best turbo with a little more top end? The most widely used turbos meeting this criteria are the VF30 and VF34. Both are the same turbo essentially, though the VF34 utilizes a ball bearing design.

What is the best turbo with a lot more top end? The most widely used turbo meeting this criteria is the VF22. The Garrett ballistic series is generally considered the king of the hill for all out performance though.

What is the best turbo with quicker spool? The most widely used turbo meeting this criteria is a P&P stock turbo.

What makes a good autocross type event turbo? The big thing to look for in a good performer for autocross use would be quick spool and more than stock flow. The TD04, TD05-16G, VF34, VF22, VF39, TD06-18G can all be considered good autocross turbos, but their particular suitability depends on the type of events where the car is generally run. During the consultation with your Vendor, discuss in depth the course length, speeds seen, gears used, and other local venue particulars to assist in determining what best suits your needs. A word of caution....before modifying or changing your turbo, be aware that this will have an effect on what class your vehicle can legally run.

Is there a way to compare Turbo A against Turbo B? Yes and no. This thread shows a comparative listing of most of the major aftermarket turbos. It compares CFM ratings of different turbos. This listing should NOT be the sole source of turbo upgrade advice though. It should be used as a general indication as to the performance level of various turbos. Matching turbos to your specific needs is where advice from Vendors and tuners comes into play. You will not be happy with the perfect tune on the wrong turbo and likewise, you will not be happy with a poor tune on the perfect turbo.

What is the best way to compare Turbo A against Turbo B? Careful interpretation of a particular turbo's compression map will give you the best determination as to what will best suit your needs. One reason for this is that Turbo A will flow XXX CFM for a 2.0 liter, and will flow YYY CFM for a 2.5 liter. Displacement can change a "perfect WRX turbo" into one that is less desirable for someone running 2.2, 2.5, or other displacement. Sadly, some turbo manufacturers do not release compressor maps to the public or even their retailers. This means that in the end, the user must consult available compressor maps as well as seek the advice of Vendors and tuning specialists for "best" suitability.

How do I interpret turbo compressor maps? General guides with examples can be found on this link, this link, this link, this link, and this link.

Where do I find turbo compressor maps?
Website 1
Website 2
Website 3
Garrett maps
Garrett maps (via their .pdf catalog)
Other turbo data

Should I upgrade my wastegate & what advantages would it give? There are a couple of different upgrades for wastegates that will help to solve different problems. Upgrading the wastegate actuator to a higher rated version will allow a higher boost threshold. For example, if a turbo has an 11 PSI actuator, with a good boost controller it can normally be adjusted to about 19-20 PSI, but no lower than 11 PSI. A 15 PSI actuator can easily be adjusted to 23-24 PSI, but again, no lower than its stated static pressure. There are also race actuators available for 19, 24, and 29 PSI. The inverse of this problem/upgrade scenario is a turbo that allows boost to rise beyond its target point. In some cases, very free flowing exhausts combined with the right supporting mods and a hot tune can cause turbos to not be able to vent through the wastegate properly. A condition that allows the car to continue to build boost beyond its target, even with the wastegate flapper in its full open position is known as "boost creep". Boost creep can be alleviated by several methods; a turbine clip can allow slightly more air to vent through the turbine blades, retuning the car to a slightly richer mix can help in some cases, and in some cases the standard size wastegate flapper can be removed, the hole enlarged, and a larger, more efficient flapper installed in its place. In some cases this will require a retune, especially if boost control is handled by the computer. The larger flapper, in most cases, will help eliminate boost creep events; however, on some of the IHI turbos, this can cause additional work to need to be performed. The IHI's are more sensitive, so on some of these turbos, the restrictor "pill" in the wastegate actuator vacuum line will need to be changed to a different size to accommodate the changed actuator duty cycle brought on by the larger flapper.

When do I go with an external wastegate? External wastegates and when to use them have become some of the most commonly asked questions in the turbo business over the past year. External wastegates move the wastegate vent from inside the turbine housing of the turbo to a remote location, fed from the same tube (or uppipe) as the turbine inlet for the turbo. There are several advantages as well as drawbacks to this setup. The first, and in many cases, the drawback that discourages most Subaru owners, is the cost. Not only are you adding expense to your turbo upgrade through the wastegate assembly, (normally starting at about $200) but there is also the additional cost of custom piping. Due to the design of the Subaru, it is more difficult than many vehicles to install/fabricate piping for the external wastegate units. This normally adds another $100-$200 in labor costs from a good exhaust shop. There are companies now offering custom uppipes with flanges for the use of external wastegates, however, due to differences in input flange on different wastegates, these are not universal. The biggest advantage to the external gate setup is boost control stability. In very high horsepower cars it becomes necessary to have a large enough port for wastegate venting that it is simply impractical to attempt the use of an internal setup. The larger external units will be able to hold the boost pressure more stable, and require very little actuation to vent fully and stop boost increase. It is this benefit that many times causes a vehicle with an external wastegate to produce additional power over an internally gated turbo, and is how the external has become known to produce more total power. Normally with proper turbo design and proper tuning, externals are not actually needed until power ranges rise into the 600 or greater HP range on a single turbo setup, and 900 or greater HP on twin turbos.

Are there any downsides to turbos? There have not been significant amounts of problems with turbos. The main downside to turbos in general is uneducated usage. Careful planning, purchasing, supporting modifications, and tuning should allow the end user long and happy usage. Too often, many users take shortcuts, exhibit poor planning, or disregard necessary precautions and end up with disappointing failures. Another downside is poor selection which leaves the user disappointed as the new turbo's characteristics don't meet their expectations. The two main disappointments are:
a. Not enough power
b. Incorrect spool characteristics for autocross drivers

Which manufacturer is best? This topic is highly debated. There are just too many factors to consider. The main category breakdowns are:
a. Price
b. Performance characteristics
c. Warranty
d. Compatibility with end user's desires
e. Bolt on or custom fabrication installation

Who manufactures turbos?
APS
AVO
Deadbolt Enterprises
Forced Performance
Garrett
IHI
Mitsubishi
Momentum
Power Enterprise
Slowboy Racing
Turbonetics

What turbo construction method is best? There is no irrefutable evidence that one construction method is better than the other. The real difference in turbo construction is the bearings. There are two main types: floating bearings and ball bearings. Ball bearing turbos were designed for increased reliability and decreased lag. Though both of these elements are true, neither advantage is especially prevalent, so the construction method should not be the main consideration when choosing an aftermarket turbo.

What is a twin-scroll turbo? Generally speaking, it is a turbo with a divided turbo inlet to isolate the pulses coming from each exhaust port to maintain more of the pulse energy from each cylinder all the way down to the turbine wheel. A twin scroll setup will respond faster and produce boost quicker than a regular turbo. Twin scroll setups are generally costlier and require more components than the average turbo ugrade to work effeciently though.

How can I decrease turbo lag? There are a number of steps that you can perform to decrease the lag:
a. A silicone Y-pipe IC hose can decrease lag
b. An aftermarket intercooler with decreased pressure drop can decrease lag, though its physical design may negate the benefit
c. An aftermarket uppipe can decrease lag
d. Port and polish turbo services can decrease lag
e. Tuning. Through the tuning of EGTs, wastegate duty cycles, and gains, spool can be accelerated. Properly tuned cars create full boost ~500 rpm sooner through these techniques.
f. Large diameter downpipes and exhaust decrease lag. If the downpipe is catless, lag with be further reduced over a high flow cat model. You also want the cat to be as far from the turbo as possible to promote quick spool.


Can I upgrade my existing turbo? Yes. Most turbo upgrade facilities offer improvement services. State your turbo, its current disappointments, and improvements you would like to see. They might offer services that can save you from buying a new turbo. Though not an all inclusive list, possible services include:
a. Port and polish: Includes heavy porting of exhaust housing, removal of flow obstructions, smoothing of the factory material, and reduction of internal angles to alter flow and evacuation. Entrance to turbo housing (where the exhaust enters the unit) is also heavily ported, removing flow obstructions and smoothing exhaust path. Wastegate pass-through from exhaust housing is also ported, increased slightly in size, and any flow obstructions removed. The most significant improvement with this service is the decreased spool time. Another improvement is the additional torque in the lower RPM band as seen in this graph. Lack of low end torque is a common complaint with 2.0L motors.
b. Internal ported and polish: This opens up the area where the air exits the compressor housing. The turbo has between 1 & 2 mm of material removed, then the rough casting edges are smoothed out. You will pick up a fraction of a HP but get better response.
c. Light clip: Clipping removes part of the turbine wheel. This allows air to pass over it faster. It will help out with high boost (16.5 PSI +) situations but will slow down spoolup.
d. Coating: Ceramic coatings keep heat inside the turbo for increased thermal efficiency.
e. Larger waste gate flapper: New technique where a large wastegate flapper is installed in place of the stock unit. The large piece covers a specially ported, larger waste gate hole in an effort to combat boost creep.
f. Changing internal turbo components: This service depends on the turbo. Generally speaking it means things such as replacing the compressor wheel with a larger unit for increased performance, changing the wastegate spring, and other internal improvements.

What questions should I ask of the retailer or manufacturer before purchasing? Once you perform your research, you should have your choices narrowed down. Before making your final decision, it is always wise to ask these questions:
1. What fuel injectors should I run?
2. What fuel pump should I run?
3. Is this turbo bolt on or does it need any special fabrication?
4. I plan on _______ racing. Is this a good turbo for my plans?
5. I plan on running the quarter mile in XX.XX. Is this a good turbo for my plans?
6. Other than a fuel pump, bigger injectors, and proper tuning, is there anything else you would recommend for increased safety and reliability?
7. What about a larger intercooler?

Will I need a bigger intercooler with a bigger turbo? This is a very hard question with many opinions and not a great deal of facts. There are quite a few aftermarket turbo users posting impressive numbers with even the stock TMIC. This isn't to say that they wouldn't benefit from a larger intercooler, but it shows that it may be considered a supporting mod worth serious discussion and consideration during or just after a turbo upgrade. This decision should be discussed with a trusted Vendor or tuner for the best advice as to what suits your needs. Refer to the FMIC FAQ and the TMIC FAQ for starting information.

What about ceramic coating or other heat wrap? Heat protections options for turbos fall under two categories:
1. Heat shielding. The primary purpose of heat shielding is to decrease heat soaking of the TMIC and other engine components. Examples of heat shielding are listed in the TMIC FAQ.
2. Turbo insulation. The primary purpose of turbo insulation is to keep the heat trapped inside the turbo for better turbo efficiency. The side effect of this is to decrease heat soaking of the TMIC and other engine components. Examples of turbo insulation are ceramic coating, Thermo Tec's wrap, or DEI's wrap.

Where do I buy aftermarket turbos? Every Subaru/Import performance store sells turbos. For purchasing, support your local economy or the NASIOC Vendors.

How hard is it to install an aftermarket turbo? Allow around one hour for install time. Professional installation, depending on your area, is around $75. This is one vehicle modification that is very simple and can be successfully accomplished by even the greenest shade tree mechanic.

How do I install an aftermarket turbo? Refer to the turbo manufacturer's instructions. For turbos without instructions, below is a link to one of the better known turbo installation instructions:
TurboXS's instructions

Is there any additional advice for turbo installation?
Materials Checklist:
SOA part # 44022AA180 Downpipe Gasket (DP to turbo) ~$20
SOA part # 44022AA150 Uppipe Gasket (uppipe to turbo) ~$11
1 qt of oil
1 qt or so of coolant (refer to the Cooling System FAQ for type)

Prior to/during turbo installation:
Pre-oil turbo
Prior to removal of any bolts, spray with a penetrant such as PB Blaster and allow to soak for 5-15 minutes
Uppipe to turbo and turbo to downpipe bolt torque spec is 26-30 ft. lbs.

After turbo installation:
Crank engine for 20 seconds to lubricate turbo (by pulling the 'IGN' fuse)
Let idle for about 30 minutes
Check for leaks and fluid levels several times
Break turbo in for a couple hundred miles (for new turbos)
Change oil after break-in (for new turbos)

Fuel Pump FAQ

What is the best fuel pump? The most commonly used fuel pump is the Walbro 342 fuel pump. It is a drop in unit that supports most aftermarket turbo fueling requirements. Other fuel pumps that are commonly used are:
a. Walbro 341 fuel pump. Functionally identical to the 342. Requires slight modification for use.
b. Supra Denso fuel pump. OEM quality fuel pump. Requires slight modification for use.

Is there anything to look out for with fuel pumps? When using aftermarket fuel pumps, many re-use the stock WRX fuel pump filter. This filter contains a hard plastic skeleton inside to prevent the pump from ingesting the soft "bag filter". Aftermarket pumps do not have the hard plastic part, and many users enjoy the additional safety that the OEM filter provides over the aftermarket fuel pump's filter.

Can I run an aftermarket fuel pump by itself without new injectors/turbo/management? During the turbo upgrade path, it may be easier to purchase and install a fuel pump ahead of time. It is cheap, easy to install, and removes an eventuality from the upgrade chain ahead of time. You can run an aftermarket fuel pump with no other modifications. Adding a fuel pump will not give you more fuel (i.e. richen your car), it simply allows for more fuel to be delivered if you run higher boost or larger injectors. The stock RRFPR keeps the pressure at the stock 43 psi + manifold pressure no matter how much fuel may be available from the pump.

How hard is it to install a fuel pump? Allow around one hour for install time. Professional installation, depending on your area, is around $75. This is one vehicle modification that is very simple and can be successfully accomplished by even the greenest shade tree mechanic.

How do I install a fuel pump? Refer to the fuel pump manufacturer's instructions. For fuel pumps without instructions, below is are some links to some of the better known fuel pump installation instructions:

scoobymods.com instructions
TurboXS's instructions
Quantum Racing's instructions

Injector FAQ

What are the best fuel injectors? Fuel injectors should be purchased based on the best possible match between the fuel flow rating and needs of your aftermarket turbo. This should be a determination by your Vendor, or better yet, a tuning professional to provide the best possible match. It is better to opt on the side of too large if there is any possibility of maxing out the injectors with your upgrade plans. Bigger is not always better with injectors so it is always best to purchase injectors best suited for your application and upgrade as need as opposed to starting off too large. This online calculator may assist you in the decision process. This post by hotrod will also help.

What type of injectors do I need? Aside from matching the injector flow for your turbo/tuning needs, you need to get the correct type for your vehicle:

WRX uses high impedance top feed injectors
STi uses high impedance side feed injectors (also called bottom feed)

What is the difference between low and high impedance? Low impedance injectors need to be electrically adapted to work properly, and usually come with the required electronic components for this.

Are there any cautions with injectors? UTEC users should be aware that they should not use low impedance injectors. There is supposed to be a fix for this sometime soon (or may be out, can someone confirm?).

What are IDCs? The injector duty cycle is the proportion of time that the injector is open, squirting fuel. When choosing injectors, many try to choose an injector size to place IDCs in the 85-90% range. This assures proper fueling with a little bit of headroom.

Is there a list of injector sizes for the WRX?

Stock WRX 420 cc
JDM STi "pinks" 550 cc (top feed)
USDM STi 550 cc (side feed)
Modified Stock WRX 600 cc
Ultimate Racing 600 cc
PE 650 cc
Helix 660 cc
Ultimate Racing 785 cc
PE 800 cc
Helix 820 cc
Modified Stock WRX 850 cc

Who manufactures injectors?

JDM STi "pinks" (for use with the WRX)
Helix
Perrin Performance
Power Enterprise (low and high impedance versions)
RC Engineering (low and high impedance versions)
Ultimate Racing (low and high impedance versions)

Who manufactures injectors for the STi?

Ultimate Racing (680 cc or 785 cc and must be used with their fuel rails)
Perrin 817 cc (modified stock injectors)
Power Enterprise 850 cc
Helix 860 cc

Can I modify stock WRX injectors for increased flow? Yes, though this route requires additional research, thought, time, and care than purchasing larger injectors.

600 cc injectors
740 cc injectors (Though this is the thread title and commonly known name, these modified injectors actually flow 850 cc when tested at the normal static fuel pressure of 43psi)

Are there any other mods to increase flow? Yes, you can modify your stock FPR when using an aftermarket fuel pump to increase the cc rate of your existing injectors. View this thread for details.

How hard is it to install fuel injectors? Allow around two hours for install time. Professional installation, depending on your area, is around $150. This vehicle modification more difficult and time consuming than most "bolt on" installations.

How do I install fuel injectors? Refer to the fuel injector manufacturer's instructions. For fuel injectors without instructions, below is a link to one of the better known fuel injector installation instructions:

TurboXS's instructions

Fuel Rail FAQ

What are fuel rails? Aftermarket fuel rails are designed to increase the internal diameter of the stock fuel lines as well as convert the OEM fuel rail set up from series to parallel. The theory behind these two changes is to increase fuel flow and equalize fuel distribution.

When are fuel rails needed? This is a very hard question without a clear answer. Two very reputable tuners and NASIOC Vendors do not believe they are necessary. god of Godspeed Inc. and nmyeti of TurboXS recently posted that they are not needed for additional fueling or fuel distribution equalization, which is the rumored cause of particular cylinder number failures. Another view by nmyeti. That being said, there is no real downside to fuel rails for people who believe they may provide an extra level of protection.

Who manufactures fuel rails?

APS
Crawford Performance
Outback Motorsports
Perrin Performance (WRX and STi)
Rocket Rails (2.5L only)
Ultimate Racing (Sti only)
Vishnu
Boomba Racing

Is there a "fuel rail mod"? Yes. Many have modified their stock (series) fuel rails into parallel fuel rails.

scoobymods.com instructions
supporting/supplemental NASIOC thread

Are their other fuel rail mods? Yes. As detailed in this thread, Ultimate Racing offers fuel injectors that mimic fuel rails by being flow matched for each individual cylinder. These injectors are specifically matched so that each cylinder flows the exact amount of cc's using the stock fuel rails. They also have flow matched units for parallel or aftermarket rails as well.

How hard is it to install fuel rails? Allow around three hours for install time. Professional installation, depending on your area, is around $200. This vehicle modification is more difficult and time consuming than most "bolt on" installations.

How do I install fuel rails? Refer to the fuel rail manufacturer's instructions. For fuel rails without instructions, below are some links to installation instructions:

Perrin's instructions
APS's instructions
Vishnu's instructions
Mike Egan's instructions
Jorge's instructions

Awesome compilation of info. Sticky this!