overboost problem...and not the good kind.

[Carl H]

well guys i typicaly dont post new topics unless i have something to say so here goes...im having some overboosting issues with the car, it seems to come and go unfortunantely but when it does happen it is repeatable.for some reason when the gate pops open at 4k and 14psi (base boost) it will overboost 1psi per 1k rpm thus having a final total of anywhere from 18-20psi at 8k.i havent leak tested the system yet but i have checked my wastegate diaphram, the blowthru maf (removed all the silicone and resealed), and my cold pipe...im currently running a hks standard wastegate with the boost source right off of the compressor cover.the downpipe off the turbine appears to have gotten crushed some how or another, but im not sure if that would impede flow to the point it would cause spiking issues.at a loss here any sudgestions are welcome.

[rbsileighty]

Sounds like a choked WG to me (progressive spike after the WG opens)... only thing throwing that idea is why it doesn't happen all of the time...

What are the conditions when it does... and when it doesn't

[Chaos the Xile]

That crushed downpipe may be the source of your problems not expelling the gasses quick enough and creating unwanted back pressure... maybe thats making the surges??

[Yellow4g63]

What about the gain on your boost controler? if it has one? or if it's fuzzy logic turn it over to simple logic and leave the fuzzy out of it.

[Shocker]

maybe a faulty diaprham as well... Althought it might be the downpipe as well, I could never explain this either I'd started noticing 2 psi is of creep by redline with my stock setup... my downpipe too I gotten slightly crushed from low ride height.. That might be doing it, increasing the backpressure, not flowing right. How big of a hassel is it to swap in a new dp?

[Carl H]

it only seems to spike horribly when its really cold out (30*f or so)...i would actualy have to fab up a new downpipe for the setup...but it needs to be done anyways.

[240z4u]

Carl what in the setup is new vs. your old engine setup?

I doubt crushed downpipe would do it at 14psi unless its almost smashed shut.

Have you tried using a mity vac or something to apply vaccum to your wastegate diaphragm to see if it bleeds out/down?

Definitely sounds like a choked WG to me too. Maybe something is wrong and the wastgate is sticking and not opening as far as the vac/boost source wants it to?

Evan

Fuzzy logic thing seems possible, are you sure there is not something messed up with your boost controller? Try bypassing it and letting the spring do the boost control and see what happens.

[USMCgetsome]

differences of cold and warm air pressure. Lube up that gate brother. Might help a lil.

[Carl H]

there isnt much diffrence int he setups really same parts and what not...i havent tested the wastegate with a vac pump yet but i am going to bypass the boost controller and see if that helps any, it could be the solenoid is actuating when its not supposed to.the problem is that the wg pops and it holds 14psi for a sec then it starts creeping...so im not sure.i know the gt30r turbine is hidiously efficient so perhaps the crushed downpipe is affecting it that much?

[Chaos the Xile]

AH the cold, well my car does the samething in 2nd gear, the boost will shoot up to about 18-20psi and kick the car sideways but as the turbo gets tuse to the cold air it stops, boosts normal after that. Weird huh?

[rbsileighty]

I just ported a WG extension/flange for this same reason tonight... it was on a A4's aftermarket manifold (prior to install)... but same logic... if the flow is obstructed somehow... by a sharp edge etc... the WG could be huge and still not flow enough air because not enough is getting to it in the first place.

Not like you're flowing a lot of air or anything with your power figures... Sounds like boost creep to me...

My stock RB25 turbo was doing this to me as well... cracks open at stock boost... and climbed all the way to 12.5 with no controller

[Carl H]

im starting to think that the problem lies within the wastegate like you guys speculate...a good friend of mine who works at rotorsports (big rotary shop) said that the same thing happens on customers cars equiped with these wastegates; they creep badly when its cold out.the REAL problem is that even tho they say its a 40mm wg its more like a 32mm measuing the outlet and when you put a piece of pipe in to it it drops to nearly 29mm...not much bigger than the std turbine outlet on the std turbo.that being said i can either try porting out the outlet to atleast 35-38mm or find a diffrent gate.

[Tictakman]

i talked to a guy at atp about sizes of wgs. he said not to even bother with a 38mm or below wg because they are just too small. he said it is common to see boost spikes with it. so, take if for what its worth...

[dsm]

I would really look into the wastegate like you said your were planning to. The crushed downpipe shouldn't cause creep because the wastegate flow is unimpeded by this, if anything it should help prevent creep. On a side note, I'd like to know about your chip service. You seem to do good work with them.

[Sil240]

Depending on how bad his DP is crushed would affect the WG.I believe his WG is routed back into the exhaust.

If the flow is being backed up in the DP, then thats going to back up the WG and then go through the turbo.