PSI Level Question.

[mshaw]

so i just installed a boost gauge on my SR20 yesterday and was looking on the internet at stock specs say boost is at 7psi, for some reason im reading 11 or 12 psi and i dont know why. Is there anythin that it could be, i didnt think you could increase boost unless u had a boost controller

[dymz999]

aftermarket actuators can easly cause stock boost to be like that. But if you have the stock actuator on the turbo then there is something else going on. is it a autometer gauge? just remember they are about as accurate as ford is great. are you taking the boost signal from the right vacuum source also?

[mshaw]

oh shit dont tell me that, yeah its an autometer gauge, my mechanic put it in but i saw him doin it and i think the boost signal is from the right vacuum source

[Aleks]

Inaccurate boost guauge. My autometer reads 16psi even tho it's 11-12 max!

[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.

[RickDaTuner]

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]

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]

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

[RickDaTuner]

but then again like you say, ever car is differnt

[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.

[RickDaTuner]

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

[legendboy]

elevation?

[dymz999]

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]

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]

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]

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

[mshaw]

which means?and how can it be fixed?

[RickDaTuner]

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]

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]

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