Trying To Work Out Why My Car Is Boosting At 11.5psi

[Galois]

i think i'll bump this as i have to look into it too. i saw >0.9 bar, or ~13-14 psi last night when chasing a guy in a monaro in my stock gtt + shitty catback exhaust from prev owner.

interesting note, between 20 and 70 out of a corner the skyline held on admirably, it didn't get away at all. never know if he was in the right gear tho...

[Galois]

I also don't buy the "exhaust gives you 2psi" shit, pressure is pressure, just because you have a more free flowing exhaust doesn't make the actuator give you an extra 2psi. It may get there faster due to better flow which might make it briefly spike over whatever your actuator pressure is, but it's not going to hold it to redline.

correct me if im wrong, but with free flowing exhaust, the pressure in the exhaust is lower for the same pressure on the other side of the exhaust turbine, higher pressure difference = higher spin speed of the exhaust turbine, higher spin speed at turbine = higher compressor speed = higher intake pressure.

I was only reffering to how a solenoid can control boost.

Ok so extreme back pressure can alter the effect of a pre determined spring rate in an actuator.

But in any case, point taken.

Back to the topic, Can anyone give any other reason as to WHY its boostin to 11.5 in an unmodified (alleged) car,

other than leaky hoses, dodgy solenoid, modified actuator, boost creep?

isn't it a solenoid that electronic boost controllers use to increase boost?

how can we tell if the ecu has been modified? my actuator looks different to yours maddowse, it has a hose leaving from the center of it. i'll have to take it out (prob on friday or weekend) to have a look at the numbers. my boost holds nicely at 13-14 psi, increasing evenly till about 4000rpm.

to check:

take the actuator apart

check vacuum hoses

will get back to you.

btw, repeating maddowse's question, do we have to adhere to the exact pipe sizes used when replacing them? because i have a fair few smillar pipes leating into bigger pipes leading back into smaller pipes. not sure if the larger pipe is just there for protection sheath type arrangement, but if its using 3 pipes instead of one thats pretty poor

[maddowse]

galios how did you go with your actuator???

i had an interesting day today !! i took an old frind of mine out for a spin and he took along something call a gtech to suposedly test my horse power rating , failed because we got like three vastly different results prob because iv never realy draged a car before to get 1/4 mile runs so i couldnt get the wheels to stop spinning and if i did i was nilly stalling it (on raceing iv ever done is on dirt (rally) the best result i got was 192hp ,

but hes been around turbos for a while (4 cilinders not 6 though ) and he seems to think my turbo is spooling up to quick and said its not ment to hit max boost instantly (like my car does) also a mate of his in another car said when im takeing off he can hear the induction which is normal but also that my blow off valve is always venting !! is this normal ??? he said in stead of hearing it go pttsssssss is sort of goes ssshhhhSHHSHSHHHHHHH lol hard to decribe in text . i dont know him well as hes not my mate but could this be posible and how do you test ??? ,

also !!!! arnt the r34 skylines ment to have a speed limiter because at we left i managed to wind the speedo past the 180km mark untill it stoped moving while i was still speading up ????

oh and anothing thing !, we noticed the car gets upto 130 heaps faster at 3/4 throttle than if i go full throttle its like i skip the boost all together ???

sorry for the long post

and ofcourse this testing was all dont in a "controlled" inviroment

[Rav3nNZ]

id i was nilly stalling it (on raceing iv ever done is on dirt (rally) the best result i got was 192hp ,

but hes been around turbos for a while (4 cilinders not 6 though ) and he seems to think my turbo is spooling up to quick and said its not ment to hit max boost instantly (like my car does) also a mate of his in another car said when im takeing off he can hear the induction which is normal but also that my blow off valve is always venting !! is this normal ??? he said in stead of hearing it go pttsssssss is sort of goes ssshhhhSHHSHSHHHHHHH lol hard to decribe in text .

sorry for the long post

and ofcourse this testing was all dont in a "controlled" inviroment

Do you have a Pod filter? i know exactly what you mean if you do, all s2 r33's and r34 gtt's have a different intake wheel than the other skylines and it sounds shit compared to other turbos.

its like a full on ssshhhhh instead of a nice loud whistle while using a pod.

who knows maybe the bov is leaking under full load idk

[maddowse]

yeah i have a pod but there is a different noise to the induction noise, when i had the standard air box the spool up sound was realy loud already just didnt hear the bov,

[maddowse]

and yeah theres no whistle its just a shhhhhhhHHHHHH noise

[Galois]

hey maddowse, that is an interesting day haha. i have found when i tested it (not on public roads) that my speed limiter came in at ~190km/h if that helps.

i took the actuator off yesterday (many scuffed knuckles haha) and took some pics. it had the number 99629 on it ind was unmodified as far as i could tell. i took some pics but don't have them with me today, will post them tonight. it had the piping in the center of the round piece, not on the side like yours. i also had a good listen and test of all the pipes but didn't notice any fatigue, they actually seemed in surprisingly good shape lol

can someone please explain how exactly the actuator works? im guessing that when the pressure gets too high it moved a plate in the actuator, which moves the rod it's connected to which opens the wastegate? lol that could be way off.

i have to find another pressure gauge to check mine is running properly.

what else could be causing the high boost if the actuator is unmodified and the hoses are fine?

[maddowse]

ok some one has explained to me about how the actuator works and its like you say !, it has a diaphram that pushes the rod ,

one this i was also told to check was the hose leading to the actuator he said to squeeze it bit by bit all the way to the actuator , aparently some people put a carby injector or block it and drill the hole smaller to restict the air, tested my one and that wasnt the case .

so your actuator is different to my one ??? you has a s2 neo yeah ? thats interesting i wonder which of us have the stock one on .

[Galois]

haha, really? lucky guess. i only thought of that while i was typing the question hahaha

mines a series 1 (1999) r34 neo, but i didnt think much changed from 1-2 engine bay wise. can anyone confirm/correct this?

yeah, our actuators are definitely different, which is weird lol. i'll have a close feel of the hose leading to the actuator and see what happens.

i have to track down another boost gauge, cos that would be an embarrassing thing not to have checked!!!

btw ill post a couple of pics up tonight

Edited May 17, 2010 by Galois

[maddowse]

ok thanks mate ,

yeah i got told lastnight if the bov is not working right then then it would result in a veriation of boost pressuer in the motor ??? can anyone comfirm this !!! also how would i test for that

[Adriano]

Have you seen if there is still a restrictor in the vacuum hose that goes to the solenoid?

[maddowse]

Have you seen if there is still a restrictor in the vacuum hose that goes to the solenoid?

is there ment to be ?? i thort that was something people put in unpurpos as a crude style of upping the boost ???

[Galois]

Have you seen if there is still a restrictor in the vacuum hose that goes to the solenoid?

i will have to check this out too lol. would this make boost greater at all times or just have a peak before dropping off? there isn't any flow through the actuator right? its just flow to the actuator, so eventually boost would level out to normal?

anyways, here are my actuator pics

[maddowse]

yeah well thats no were near what my on looks like !!, hopefully someone can let us know which is the standard out of the two ????

[RBceffy25]

isn't it a solenoid that electronic boost controllers use to increase boost?

how can we tell if the ecu has been modified?

A solenoid is the electronic sensor that mesures the actuator pressure vs compressor pressure (and manifold pressure for some aftermarket makes) and decides wether or not to bleed boost in order to control boost. All of our RB's use them standard from factory as well as many, many other cars/engines I know of.

you may just want to take it to a dyno shop/tuner, throw it on the dyno and have a real look at whats going on with everything. I am sure anyone you take it to wil be able to help you in some way. Not expensive either, I think its usually about $60-$80 for a power run and check A/F ratio's etc... Not to mention these people deal with these sorts of problems for a living on a daily basis.

Sorry dude's, I dunno what else may help you?

[Galois]

that's a really good point mate, they can monitor boost pressure and power and give some idea of what's happening. for example, i am not completely sure that my pressure sensor is working properly, and if i'm only putting out like 150-160rwkw its prob running stock boost.

wont be able to do that for a couple of weeks tho...

[32vspec2gtr]

Hey guys, my gtr had a similar issue that turned out to be a vac/boost line and faulty air flow meter giving me different things.

Firstly i would be checking the vacum lines and seeing if they are split like someone else has said previously. THAT IS ALL LINES IN THE SYSTEM! what i mean by this is every single line that comes off the cold outlet side of the turbo all the way into the engine. If one of these are leaking it can be the cause. This will also make a hissing noise.

Next i would be flashing codes out (easy to do just pin out the diag conectors as per the service manual) and checking that you don't have any wiring or sensor issues. Also clean the airflow meters with electrical cleaner as this can also give you a false reading due to contamination of the air filter oil used on pods.

Then check the wastegate and the wastegate flap on the turbo as it can seize up.

Also check that you don't have any boost leaks through your hoses that the main air flows through, etc as this can give you poor boost performance ect.

As for how the wastegate works, it takes boost pressure in the intake manifold or outlet of the cold side of the turbo and this acts on the wastegate. No matter what the exhaust is doing it should not affect the boost other than restrict it due to a colapsed cat and so make less boost. So you will only have a more pronouced boost spike not more boost as previously stated. The internals of a wastegate are a spring and a diaphram. The spring holds the wastegate shut and the boost pushes on the diaphram to open the wastegate. If this diaphram is split or has a hole internally it can cause excessive boost and also make a hissing noise as the boost pressure pushes past.

The blow off valve is the same sort of design only that the vacum created by the shut throttle body opens the valve and allows the air to escape. So the same goes for this diaphram.

Chasing boost leaks etc is difficult when you don't have the equipment. I can do it at work on the trucks i work on but on the gtr is a harder thing to do. I recommend you take it to a dyno and do a power run and let them see whats happening. They found out what mine was doing and i got all the lines replaced for a couple of hours and all up cost me something like $400. Cheap when you consider a turbo is a lot more let alone a engine if it over boosts and leans out.

Anyway hope this helps you guys out. Kinda hard to point you in the right direction with out hearing it in person.

Matt

[maddowse]

thanks for the help guys ill look into getting a power run !! i didnt know it was so cheap

thanks again

[Galois]

have you done the run yet maddowse? or did you pass on that idea once you knew what the actuator was set at?

i think i'll take my actuator off and see if i can check the pressure it's set at at work, good times lol

[Galois]

how do i know what the actuator is set at? i put it under pressure at work and the actuator started moving at 7 or 8 psi and was fully open at 14. so which is the actuator set at??

thanks guys