Car Is Still Overboosting

[3LGODZILA]

ok this is really turning into a major pain in the ass. my previous topic (overboosting with split dump/front screamer pipe) http://www.skylinesaustralia.com/forums/Ov...23#entry5150823

so ive done the tests and listened to the people and got rid of the JJR split dump/front pipe and replaced it with the 3inch bellmouth front/dump pipe i previously had on the car which had no issues before. beleive it or not the car is sill overboosting but i dont think as bad as before.

ok so i went for a test drive, in 2nd gear by about 5500-6000rpm boost was around 18psi and then something weird happend, the car felt as if it lost a bit of power for a second then gained it back while i was watching the boost gauge the boost went down to about 16 then back up to 18 at this point i was at 7000rpm. now ive hit boost cut before (when a workshop wound my standard turbo up to 15psi instead of tuning my safc) and this definately wasnt the same power loss as when i hit boost cut bofore.

if anyone hasnt read the previous topic i made: car is running a basic highflowed turbo, full 3inch exhaust, fmic, no boost controller the wastegate is straight off the manifold pressure.

the only thing i can think of is the wastegate. when i pumped compressed air into it before it onli moved half way (and it definately wasnt fouling on the dump pipe) im assuming this is the preload on the actuator but if i loosen this off i wont be able to hold boost properly.

suggestions? cheers fellas

[Pal]

what sort of ecu you running, had this problem with my high flow when i was using standard injectors and safc2, kept on wanting to go to 15 - 16 psi when i only wanted 10( i ported the wastegate hole but didnt do anything) . had to put a restriction plate in the exhaust down to 2 3/8" and this held about 11 psi. after i put in the 550cc's and power fc it went away i pulled the restriction plate and boost sat where i wanted it. i think it may have the tune (too rich) dont think the safc is good enough to control this set up

[NSNPWR]

Couple of things-

The wastegate does not ever fully open to 90 degrees, yours sounds about right at 45 or so...so dont bother with that, its working....

Are you running a Full 3" exhaust with Decat pipe? Decat exhaust are a known contributor to uncontrolable boost...as the post above shows, placing a restriction in the exhaust fixed the problem...and a cat is a great restriction....especially a factory pos....

I had this issue on my last car, ADM S15, was running full 3" with Decat plus various other mods, fitted a disco (with the tight 0.64 rear hsng) to it and had major boost control issues...I fluked a fix on mine when I reconnected the factory BOV which appeared to bleed off some boost above 15psi...before I did this it seemed to wanna make unlimited boost...scary.

Best way to check whether its a wastegate size issue (which is likely the case with a Hiflow running a small internal gate) is to disconnect the actuator rod from the wastegate swing arm, move the rid to the side, drive the car, load it up through the rev range, it will be laggy as gosh darn, if it still makes 18psi like this then youre internal gate is too small and/or your exhaust is too free flowing.

[MrStabby]

I can only think it will be the wastegate actuator malfunctioning or a leak in the boost signal to the wastegate actuator. I'd replace all the signal tubing first, and if that doesnt work try a new wastegate actuator.

[3LGODZILA]

yeah ive got a 3inch decat pipe so the exhaust is pretty free flowing.

by signal tubing do u mean all the vac lines? ive replaced all them with aftermarket silicone stuff

and yes its standard ecu ive got an safc but its unplugged as id rather it be rich then lean. ive got an rb20 ecu with a nistune board and vct switch ready to go in the car and get tuned but i thought i should get this prob fixed before i get that tuned.

pal, how did the aftermarket ecu stop the boost from creeping?

[MrStabby]

by signal tubing do u mean all the vac lines? ive replaced all them with aftermarket silicone stuff

Yeah i mean the vac (or boost) lines. Maybe re-route your boost gauge to tee it off just before the actuator to check that the actuator is seeing full boost. Otherwise try another actuator. I have no good ideas....

Agree that ecu wouldn't be related to boost creep, but I cant explain what Pal saw on his car.

[NSNPWR]

Stick the cat back in and it will fix the issue....and rob you of HP...but you dont really have much of a choice if you wanna control boost with that internally gated hiflowed turbo.....as Pal said, he put a restrictor in the exhaust and it held 11psi, not sure either where the connection is between ECU/Injectors and overboosting....

If as I mentioned above you do a very quick and simple test, disconnect the actuator rod from wastegate swing arm and drive it...if it still makes sh1tloads of boost then you need to restrict the exhaust, bleed off boost through some means or try porting the internal gate right out and put like an XR6 turbo wastegate flap in there...

This issue is very common...perhaps speak to the Turbo builder about it and the decat etc...when I was having this issue I spoke with Bill at ATS, Adam at Allan engineering in Adelaide and Kyle (6BOOST) and all suggested that the combination of a free-flowing exhaust (decat) with a small internally gated hiflowed turbo was an ideal combo to create this issue...

Edited April 4, 2010 by NSNPWR

[Adriano]

I can see how a stock ecu could cause boost control issues, there is a bucketload of fuel and retarded ignition timing, which is halfway towards antilag.

[MrStabby]

I can see how a stock ecu could cause boost control issues, there is a bucketload of fuel and retarded ignition timing, which is halfway towards antilag.

Surely that would cause underboosting not overboosting?

[DVS JEZ]

just tune it to suit and let the good times roll

[Pal]

rich tune =too much fuel = more burn = more exhaust gasses = more boost. need to slow down the gasses or get a good tune, that is where the restrictor plate comes in (or cat) this is widely used on 2j motors to stop overboosting.

[zebra]

running rich lowers EGT's so that wont cause over boosting (in fact this is why most production turbo motors run hugely rich from factory)

running lean and with retarded ignition timing will increase EGTs massivley and can cause the turbo to over boost.

which is probably why a good tune fixed any boost issues.

[3LGODZILA]

just tune it to suit and let the good times roll

yea thats what i was thinking. im planning to run around 18psi tuned anyways so i spose if its not going over 18 im happy with that. i just didnt want to put it on the dyno and get everything tuned to only find out its boosting over 18psi.

i know i might hav to, but i dont like the idea of spending a few hundred on a cat thats gonna make my car slower