PSI Level Question. [Archive] - Beyond.ca - Car Forums

RickDaTuner

09-27-2005, 10:13 PM

Originally posted by dymz999
Boost reads (digitally) on my greddy profec B II are 9 - 10 psi right now. Autometer gauge is showing up at 14 - 15 psi. Mechanical gauges when it comes to boost i don't think are so grand. I wonder how sensitive the diaphrams inside them are?

Also if he took the source from the wrong spot it could cause issues. Make sure he didn't tee off the Blow off valve line, seriously its not cool.

the BOV/BPV and the Intake manifold are the most responsive places to set up a T for a boost gauge..... why wouldnt he want to tap a boost gauge line in there?

dymz999

09-27-2005, 10:20 PM

Tapping the blow off valve line specifically can cause the blow off valve to not function properly, hence people are always told and should ALWAYS tap the line that runs to the fuel pressure regulator. It is not the best place on a nissan, well at least on most of the engines...

Also the blow off valve sources comes from the intake manifold but the port for it is larger than the fuel pressure regulator port.

RickDaTuner

09-27-2005, 10:27 PM

Originally posted by dymz999
Tapping the blow off valve line specifically can cause the blow off valve to not function properly, hence people are always told and should ALWAYS tap the line that runs to the fuel pressure regulator. It is not the best place on a nissan, well at least on most of the engines...

Also the blow off valve sources comes from the intake manifold but the port for it is larger than the fuel pressure regulator port.

the only way i see it not allowing the BOV to not funtion properly is if you dont leave enough line between the valve and the tap, wich would cause turbulance in the line, the only other place where i would see a problem is if the tap caused a kink in the vaccum line, its pretty safe man, so long as you tap it properly...

Subaru Recomends that you tap it there:dunno:

RickDaTuner

09-27-2005, 10:28 PM

but then again like you say, ever car is differnt :thumbsup:

dymz999

09-28-2005, 06:50 AM

I dont give a damn what some australian car maker says because the FSM (factory service manual) for our engine specifically states not to do so. Best location to take from is the line running to the fuel pressure regulator bar none.

Now another thing that could cause the boost spike is if you have the stock boost solenoid hooked up. This stupid thing is supposed to make sure the boost is at a constant 7psi, however if it was messed up, aka the diaphram inside was cracked it would pull way more vacuum than it is supposed to.

What rpm range are you seeing the higher boost level come on at? that can give us a rough idea if its the gauge or something else. you should be seeing that much boost until at least around 4,500 rpm and higher.

RickDaTuner

09-28-2005, 08:17 AM

Originally posted by dymz999
I dont give a damn what some australian car maker says because the FSM (factory service manual) for our engine specifically states not to do so. Best location to take from is the line running to the fuel pressure regulator bar none.

Now another thing that could cause the boost spike is if you have the stock boost solenoid hooked up. This stupid thing is supposed to make sure the boost is at a constant 7psi, however if it was messed up, aka the diaphram inside was cracked it would pull way more vacuum than it is supposed to.

What rpm range are you seeing the higher boost level come on at? that can give us a rough idea if its the gauge or something else. you should be seeing that much boost until at least around 4,500 rpm and higher.

Subaru Is Japanese.. and if the car manufacture states not to place it there, then so be it :nut:

legendboy

09-28-2005, 08:33 AM

elevation?

dymz999

09-28-2005, 08:48 AM

I dont think elevation could effect it that much. that is 1.0 Bar of boost which is .5 bar more than stock. either the gauge is screwy or something else. If anything it would less you'd think. I know at our elevation the compression on our motors should be roughly 10psi less than one factory specs state. Factory specs states 155psi and the actual pressure is closer to 145psi.

Sounds more like it is spiking to me. The boost solenoid being screwd is always a possibility...

Although is this a CA18 or an SR20. I'm not 100% sure if CA18's had the boost solenoid sine they had the vacuum port right from the turbo...

RickDaTuner

09-28-2005, 09:23 AM

Going back to the orginal question, does the needle fluctuate at all or does it just hit 14-15 PSI and just stay there, when you go WOT from a cruise does your Boost gauge bounce up and down befor it settles in its place?

if it hits 7 psi and then start to climb slowly, then this is boost Creep, if it goes up to 15 psi then comes back down then its boost spike,

boost spike is caused by a laggy Boost selenoid wich could also be called the Waste Gate Selinoid, Boost creep is cause air flow inefficientcy(sp) on the waste gate side of things.

bolth can be contributed to lower altitudes or colder, denser air.

if it boost creep then you either need to enlarge your Waste gate Flapper or port and polish the hot side of the turbo to allow for more unrestriced, smoother flow.

if its boost spike then you might want to change out your stock Selenoid for a bigger one or a dual selenoid set up that would be found on a AVC-R.

of course this may all be caused by improperly calibrated Boost gauge

FYI from the info that i have been reading up on the Waster gate selenoid is the best place to tap for your Boost gauge or any other Vaccum line that is pre throttle Body, also from the comments i was reading from other fellow SR20 owners, it seems that the FPR vac line isnt the best place either, sue to the fact that it lowers the Reliability of the car, should that line ever degrade and become leaky or pop off all together...

your best bet would be to get a friend and test his gauge on your car and see if you get the same results

mshaw

09-28-2005, 10:00 AM

yeah thats what i was thinkin of doing, and to a previous question on here, i hit about 4 psi at 2000 rpms or so and at about 4000 hit 12 and it stays there, it doesnt hit seven and creep up so i guess i have boost spike going on

RickDaTuner

09-28-2005, 10:36 AM

Originally posted by mshaw
yeah thats what i was thinkin of doing, and to a previous question on here, i hit about 4 psi at 2000 rpms or so and at about 4000 hit 12 and it stays there, it doesnt hit seven and creep up so i guess i have boost spike going on

its not Boost spike, boost spike as I wrote earlier is when the needle Jumps up to 15 PSI then comes back down to its regular Pressure... if it just goes all the way up when its not supposed too then that is called Over boost:thumbsup:

mshaw

09-28-2005, 10:48 AM

which means?and how can it be fixed?

RickDaTuner

09-28-2005, 10:50 AM

a stab in the dark might be that you have a sticky/semi ceased WGV selenoid wich opens initaily but then get stuck and wont open further resulting in the Said boost numbers, but is still capable of opening and closing

dymz999

09-28-2005, 01:05 PM

The person who tuned my ecu and likely the best resource on these engines even told me to tap the FPR line. For the record it does not degrade the performance of the engine. Why do you want the source coming from there?

Answer: If you take the boost readings pre-throttle body aka just outside of the turbo like he is suggesting it will not give an accurate reading of the boost reaching the engine. You want to use the closest thing to the engine itself for getting the boost readings because this will tell you precisely what the engine is seeing, not what the turbo is producing.

Lastly, how does your car idle and how much vacuum is it pulling at idle? Please do me a favour and put the car in neutral with the e-brake on and rev it to around 5,000 rpm. Please tell me if you see any boost. I'm thinking this could be your problem, it sounds like you could be running extremely rich or the timing could be just off. When this happens extra fuel will cause the turbo to spool way more than it should. Check that out, it could easily be the case. You could also take your spark plugs out and tell us what color they are.

BUT for the love of god, take the boost signal from the intake manifold. For the record, the instructions greddy gives you even says to do this.

Also if your actuator were going bad (we don't have wastegates you fool) then the boost would actually be lower and wouldn't hold higher amounts of boost.

RickDaTuner

09-28-2005, 01:46 PM

Originally posted by dymz999
The person who tuned my ecu and likely the best resource on these engines even told me to tap the FPR line. For the record it does not degrade the performance of the engine. Why do you want the source coming from there?

Answer: If you take the boost readings pre-throttle body aka just outside of the turbo like he is suggesting it will not give an accurate reading of the boost reaching the engine. You want to use the closest thing to the engine itself for getting the boost readings because this will tell you precisely what the engine is seeing, not what the turbo is producing.

I really dont understand where you have gotten you cockyness from? your information is nothing more than bench Tuning and for the most part WRONG!. you will always want to know what your Turbo is putting out before the charged air even hits the engine, the faster you can determine a boost problem the greater chance you have at saving your engine

FYI the FPR tap comes from a pre throttle body source

and I didnt say that it affects performance, i said it affects reliability...

BUT for the love of god, take the boost signal from the intake manifold. For the record, the instructions greddy gives you even says to do this.

Also if your actuator were going bad (we don't have wastegates you fool) then the boost would actually be lower and wouldn't hold higher amounts of boost.

You do as a matter of Fact have a wastegates on your T25/ or T28 variant, all gas turbo's do unless they have custom diverter valves, wich are inefficient and clumsy.

A waste gate will always be closed when it is not in use since there is a nice heavy spring there to insure that, the actuators Job is to open it and regulate exhaust gas flow, a closed gate will result in full boost... a sticky gate will result in over boost... no waste gate would be full boost all the time with out any controll the only time the end result would be low boost is cracked housing or a broken spring

you may have a SR20 under the hood of your car, but your certainly dont know the workings of it..

quit being so arrogant and help find a solutiuon

mshaw

09-28-2005, 03:04 PM

man people arguing i dont know who knows, i will tell you later tonight when i have tested it and tell you what the boost reads and what the vacuum is at idle, i think i will probably take a pic and post it where i have the boost gauge coming too in the engine

dymz999

09-28-2005, 03:15 PM

I'll say this one more time, quite blunt your a blabbering idiot now go away and never come back.

SR20 engines, the FPR port is not i repeat NOT pre throttle body. It comes right off the intake manifold. The boost rate coming from the turbo doesn't mean nothing as it is not the factual amount of boost hitting the engine. Who cares if the turbo makes 18psi when the engine is seeing 20psi which in most cases is the situation.

I'll tell you this much you are a crappy internet mechanic. I do have an SR20 and know just about as much as one can. I recently had the "joy" of rebuilding the engine and upgrading everything.

yes the engines do have a wastegate, it is internal however and controlled by a set amount of vacuum going to the actuator rod which in turn opens and closes the wastegate. however when a wastegate goes bad it will cause the boost to be less not more. because the amount of vacuum going towards the actuator creates a leak in the diaphram which causes less pressure in the actuator arm and the wastegate is then open more thus allowing less boost. Not all actuators see exhaust gases, actuators are used on all Nissan engines i have worked on that are turbocharged. This is how they work down to a tee. This is the opposite of what is happening.

Now then, i'll re-itterate this, you dont know nothing about these engines so why try to help people with them with useless information? Unfortunately i have a lot of accurate information i can share on them from my own experiences. For the record you shouldn't insult people when you dont know anything about them, in this case my friend you were dead wrong. I'm not trying to argue here, i'm trying to give you accurate information so you can solve your problem. listening to someone who is giving you "generic information" will get you know where when you need specific help.

86max

09-28-2005, 03:24 PM

I HAVE AN SR20 TOO!

http://www.webace.com.au/~gburger/contacts/oct2001/Fighting%20Children.jpg

Dymz, No need to argue if someone doesn't agree with you man.

Mshaw, if you want a more accurate boost gauge pm me.

RickDaTuner

09-28-2005, 03:42 PM

yeah 86max will hel p you out good man :thumbsup:

dymz999

09-28-2005, 03:48 PM

Wow dont know where you pull your garbage from, man I get my stuff from the FACTORY SERVICE MANUAL which is what people should read for the answers.

a) FPR port comes from the intake manifold right above the throttle body but after the throttle body itself.

b) it uses an internal wastegate that has a flapper and an actuator. when the actuator goes bad the turbo will not produce as much boost.

c) the most accurate measurement of boost is obtained from the intake manifold itself. Aka this is how much boost is actually going into the engine. If you place the boost line out of the hotpipe you'll get how much air the turbo is producing but not how much is going into the engine.

d) when the base timing of the engine is off (retarded) it will cause you to be able to make more boost than normal as there will be excess fuel which is being burned off which causes the turbo to spool way more than it normally does. (this is similar to people in japan who inject nitrous oxide into the turbo of a T88 to make it spool instantly.

Not a matter of arguing, but people giving generic information to specific problems is just wrong. I still find this all kind of funny though. Considering all i've done with these engines to have some subaru dude tell me this and that is really kinda funny. Especially when he clearly knows jack about the engine(s) in question.

RickDaTuner

09-28-2005, 03:57 PM

Originally posted by dymz999
Not a matter of arguing, but people giving generic information to specific problems is just wrong. I still find this all kind of funny though. Considering all i've done with these engines to have some subaru dude tell me this and that is really kinda funny. Especially when he clearly knows jack about the engine(s) in question.

:rolleyes: so hows that small penis treatin you?:D

dj_rice

09-28-2005, 06:17 PM

Originally posted by RickDaTuner

:rolleyes: so hows that small penis treatin you?:D

:rofl: :rofl: :rofl: :rofl: :rofl: :rofl:

EK 2.0

09-28-2005, 08:40 PM

Originally posted by dymz999
I'll say this one more time, quite blunt your a blabbering idiot now go away and never come back.

Now then, i'll re-itterate this, you dont know nothing about these engines so why try to help people with them with useless information? Unfortunately i have a lot of accurate information i can share on them from my own experiences. For the record you shouldn't insult people when you dont know anything about them, in this case my friend you were dead wrong. I'm not trying to argue here, i'm trying to give you accurate information so you can solve your problem. listening to someone who is giving you "generic information" will get you know where when you need specific help.

how is your "I drove over railroad tracks and blew-up my SR motor" doing??:rolleyes:

mshaw

09-28-2005, 09:39 PM

so to earlier questions my vacuum in neutral is sittin at about 15 in.Hg and when i rev pretty hard to about 5500 revs i get about 2 psi, slowly doing it does nothing, i dont really feel like taking a picture but if it will help the solution i will for sure snap a quickie and put it on here

dymz999

09-28-2005, 10:12 PM

EK 2.0 i dunno, 9:1 compression SR20 motor is pretty nice and fun to drive right now.

Now back to the point, normally you shouldn't be able to make any boost in neutral. Is the boost at 2psi fairly constant each time? If it were a timing issue you'd be likely seeing full boost by 5,000 RPM in neutral. If your coming to the NECC meet on sunday i can bring my spare gauge so you can verify its correct if you want...

mshaw

09-28-2005, 10:41 PM

u know what i may do that actually, kinda busy that day though, what time is it goin on?

pressure_ratio

09-29-2005, 11:52 AM

Originally posted by Aleks
Inaccurate boost guauge. My autometer reads 16psi even tho it's 11-12 max! :nut:

Originally posted by legendboy
elevation?

Why do people not realize this :banghead:
Gauges are calibrated at sealevel,when you go up the readings do also.
You can't depend on factory boost specs either for the same reason.

mshaw

10-02-2005, 04:44 PM

so does that mean that all boost gauges in calgary would be off by a couple psi that doesnt make sense

dymz999

10-02-2005, 09:40 PM

Up at this elevation our pressure would most likely drop if i'm correct as the air is actually thinner. This is why i was told when doing a compression check on motors you can expect slightly lower compression than an engine say in vancouver since our elevation is higher.

RickDaTuner

10-02-2005, 09:49 PM

Originally posted by pressure_ratio

Why do people not realize this :banghead:
Gauges are calibrated at sealevel,when you go up the readings do also.
You can't depend on factory boost specs either for the same reason.

if the engine is desinged to regulate the Turbo for 7psi, then its going to make 7psi worth of boost either at see level or 3000ft of elevation.
It will only go down as altitude increases, and even then you would have to be pretty high before a turbo wont make its factory level Boost due to altitude...

gauges may be calibrated at sea level but if there is 7 psi worth of boost going into the engine, then its going to also read 7 psi of boost at the gauge since boost is static and not dynamic, if a gauge was going to read higher or lower due to altitude you would see that with the car turned off (the gauge would Read Positive or negative with the engine off)

they do read off though, due to miss calibrated Diaphrams in the gauge itself,

what does read actuall main sea level pressure regardless of your altitude is the MAP sensor, these are sealed and calibrated to sea level

dymz999

10-03-2005, 11:53 AM

Mleh, your "somewhat correct". Maybe now explain to him why 7 psi on a T25 and a T28 is actually not the same....

also explain why your vacuum will increase by 1 to 2 psi when you go from calgary to vancouver...

RickDaTuner

10-03-2005, 12:26 PM

Originally posted by dymz999
Mleh, your "somewhat correct". Maybe now explain to him why 7 psi on a T25 and a T28 is actually not the same....

also explain why your vacuum will increase by 1 to 2 psi when you go from calgary to vancouver...

are you fishing for faults, or testing my knowledge?
How about you add on to whats missing:thumbsup:

This Forum is a constructive one, I am not here to prove my intelligence is greater than yours. :drama:

pressure_ratio

10-03-2005, 01:02 PM

Originally posted by RickDaTuner

if the engine is desinged to regulate the Turbo for 7psi, then its going to make 7psi worth of boost either at see level or 3000ft of elevation.
It will only go down as altitude increases, and even then you would have to be pretty high before a turbo wont make its factory level Boost due to altitude...

gauges may be calibrated at sea level but if there is 7 psi worth of boost going into the engine, then its going to also read 7 psi of boost at the gauge since boost is static and not dynamic, if a gauge was going to read higher or lower due to altitude you would see that with the car turned off (the gauge would Read Positive or negative with the engine off)

they do read off though, due to miss calibrated Diaphrams in the gauge itself,

what does read actuall main sea level pressure regardless of your altitude is the MAP sensor, these are sealed and calibrated to sea level

I agree with you somewhat but temprature and air pressure will have an effect on your boost level.Look at the altimeter setting in an aircraft,it constantly needs to be updated acording to barometric and weather conditions,you can be several hundered even thousand feet off.

Any pressure gauge works on differential pressure.Pressure between what ever the signal is vs. outside air pressure.If the outside air pressure changes from altitude,air temp,humidity your reading on the gauge will change also.Similar to a barometer.

The reason an SAFC or whatever piggyback you may be using will read different than your gauge is they use a map sensor which reads absolute pressure,which isn't affected by outside conditions.

There are a lot of factors that could change the stock boost level.Bolt on an exhaust,intake,etc and it will change also.

RickDaTuner

10-03-2005, 01:12 PM

Originally posted by pressure_ratio

I agree with you somewhat but temprature and air pressure will have an effect on your boost level.Look at the altimeter setting in an aircraft,it constantly needs to be updated acording to barometric and weather conditions,you can be several hundered even thousand feet off.

Any pressure gauge works on differential pressure.Pressure between what ever the signal is vs. outside air pressure.If the outside air pressure changes from altitude,air temp,humidity your reading on the gauge will change also.Similar to a barometer.

The reason an SAFC or whatever piggyback you may be using will read different than your gauge is they use a map sensor which reads absolute pressure,which isn't affected by outside conditions.

There are a lot of factors that could change the stock boost level.Bolt on an exhaust,intake,etc and it will change also.

I also agree with you on the above info, but Boost gauges used in cars are nothing more than a Open diaphram, they arent sealed units like altimeters, or Map sensors.

when pressure is applied to the Diaphram it will expand or contract(vaccum) and no matter what the tempeture or altitude reading will always be the same. it will always be the same because thier O psi/vaccum reading is reset everytime the car tuen off due to its open diaphram, basically they are nothing more than over Glorified Tire pressure gauges...

as for the other factors that can change Boost such as exhaust or intake, this is mainly the fault of the Stock turbo components not being able to handle the increase of CFm, that bolt on mods such as exhaust or intakes bring with them...