[BiturboS4] boost pressure decreasing...

Michael Kuriger michael at isuzu-mods.com
Thu Mar 6 16:05:49 EST 2003

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here's a few things to check:
air filter
cats <== biggie with turbo cars running high boost
leaky blow off valve(s)
inacurate boost gauge

Mike Kuriger
01 S4 avant perl white giac-x
89 isuzu imark rs turbo 400HP drag car
91 isuzu impulse rs turbo awd show car

California Fields wrote:

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>I've noticed that my peak boost is no longer around 16-17 psi as was the case
>when I first installed my GIAC-X and boost gauge.  The peak boost now reaches
>about 15psi, and that's usually only when I floor it in a tall gear (5th or
>6th) at lower rpms (2,500-3,500rpms).  When I really rev it up (>4500rpms), it
>is more around 12-14psi...whereas before it seemed to hover right around 15psi
>until above 5500rpm when it would taper off slowly.
>Could this mean that I have a boost leak somewhere? Or, could this be a sign
>that the turbos are going?  I haven't really noticed any other symptoms except
>*maybe* a slightly louder turbo siren whine (but hard to say).  No DTCs
>detected by VAG-COM.
>Any input helpful. Thanks.
>Carter Fields, San Francisco
>2001.5, GIAC-X, Miltek 3" cat-back, Strat. shifter, Strat. DVs, A-pillar boost
>>From: Matt twentyV
>>To: BiturboS4 at audifans.com
>>Subject: [BiturboS4] V8 Tuning Potential
>>Date: Fri, 31 Jan 2003 14:16:08 -0800 (PST)
>>So we've had this debate now about whether the V8 S4
>>could be tuned to 400hp. So I went to look at
>>tuning options for BMW- which like the upcoming S4,
>>uses highly tuned NA engines out the door.
>>In a nutshell, forget it unless you add a
>>For the E36 M3, you can find exhaust and chip
>>combinations that have dyno data showing 10-15hp
>>increases. There are also a few supercharger kits
>>out there that advertise 80hp or so at 8psi.. $6k.
>>For the E46, some tuners claim 7-8hp increase but
>>don't show dyno graphs. I found one supercharger
>>kit for the E46 330i
>>For the E46 M3, there is
>>some message board activity indicating AC Schnitzer
>>is developing a system that will reach 400hp... for
>>$13k!! I'm guessing that involves an entire rebuild
>>to use new pistons to reduce the 11.5:1 CR. As
>>someone already mentioned, adding boost to an engine
>>at that high a CR is problematic.
>>Matt Rooke
>>'91cq- 20vt chipped
>>'00S4- 30vtt stock
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