Overboost?

1335 Views 3 Replies 3 Participants Last post by HondaH8er, Apr 23, 2002

markuswarren

Discussion Starter · Apr 8, 2002

first things first, I'm a brit, secondly, I've x-posted this from scoobynet, because you guys might give a better response

Right, hoping to try and find an answer to this.
Car: My94 WRX Wagon. BPM Twindump Downpipe into Apexi N1 center and backbox. Thus it's decatted.

After fitting the downpipe I'm getting what I believe is overboost. here's what happens.

If I plant the old foot to the floor then boost gauge jumps up to 0.9 bar, then it immediatly drops down to around 0.5 bar, then back up to 0.9, then down to 0.5 then back up, then it stays up.
Is this over boost? if not then what is it?
A few people have said that the ECU could be detecting Det and retarding the ignition, thus causing the problem. could this be true? (I'm running purley on optimax)

I seem to recall that fitting a 3mm (wrong size?) restrictor *somewhere* will fix it, is this true? if so then what size restrictior, and exactly where do you fit it.
Is this an easy/cheap thing to fix?
It's a tad annyoing, plus I want to RR the car and this overboost will muck up the info from the dyno (or am I wrong?)
thanks for any info or help

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Graham

· #2 · Apr 9, 2002

Well, where SHOULD the stock boost level be?

If its supposed to be at .9 BAR (13.2 psi), then you might have some sort of a wastegate problem.

Do you have a manual/electronic boost control system on the car?

There's obviously something wrong with the turbo, but retarding timing won't just pull half your boost like that.

Graham

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markuswarren

Discussion Starter · #3 · Apr 9, 2002

Pretty sure stock boost level is 0.9 bar

I no fancy boost control gizmos on the car, and stock ECU as far as I can tell.

I think the reason it occurs is simply because the turbo now spools up way quicker than it did before, due to it being a free flow system now with no cats in it.

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HondaH8er

· #4 · Apr 23, 2002

markuswarren said:
Pretty sure stock boost level is 0.9 bar

I no fancy boost control gizmos on the car, and stock ECU as far as I can tell.

I think the reason it occurs is simply because the turbo now spools up way quicker than it did before, due to it being a free flow system now with no cats in it.

I gotta agree with Graham about it possibly being a a wastegate/blow-off valve problem (I've never had a turbo, so I still get those confused sometimes). A free-flowing exhaust will definitely help the turbos spool up faster, but that's won't cause a 0.4 bar drop in boost. On the contrary, I would think the boost would jump up to the max quickly, and stay right there, as long as you keep your foot mashed to the floor. If you keep your foot in it, and the boost is up and down like you describe, it sounds to me like you have a leak or a bad valve in the intake charge tubing.

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