[BiturboS4] RE: Hesitation....and now...Catbacks

jysap at cs.com jysap at cs.com
Thu Oct 24 22:14:11 EDT 2002


Can u expand on your point:

>This should not be much of
>a problem with the cat-back (which IMO just changes the noise, not much

Have u done a dyno of an S4 with a stock exhaust vs. catback vs. no-cat exhaust (under the same conditions)to get a basis for your statement? Without making such a comparison, I couldn't see how u could render such an opinion. Maybe you (or someone else) has and could pass such info to the list, as a public service announcement.

Y2K S4
86 951

"Edwards, Dave" <Dave_Edwards at iOra.com> wrote:

>On Wed, 2002-10-23 at 16:45, California Fields wrote:
>> in the gas pedal (like a turbo lag or something).  It's kind of hard
>> to explain but does this sound normal?  Here's an example of the
>> delayed
>> response:  I'm cruising along in 3rd gear at about 3k rpm...I abruptly
>> the throttle down from about 10% (cruising) to half way and hold it....the
>> lurches forward with strong force but then the power backs off a
>bit...kind of
>> like there was an initial spike of pressure but then it equilibrates to a
>> plateau of power (still accelerating strong but just not AS strong)...kind
>> like I pulled back on the throttle when I really hadn't.  Is this a normal
>I'd take a long, hard look at your bypass valves.
>I was having the same symptoms on my stock S4 Avant; dealer said, "Oh, they
>all do that after 15k miles or so..." Uh huh, sure. So I bought myself two
>new bypass valves, installed them, and voila! The lumpy, irregular power
>delivery is gone...
>I'd imagine that the symptoms would be even more noticeable with a chipped
>car and higher boost levels.
>2001 S4 Avant 6spd
>I agree - sounds like sticking valves. If you still have the stock Bosch
>valves, get rid of them, like yesterday. I'll add two more points:
>1) Don't expect a chipped car to be a smooth as a stock one. ECU mapping is
>a compromise and you've gone for performance at the expense of some things.
>2) If the chip is not mapped to cope with changes in the exhaust system then
>indeed it can suffer, mainly by running too lean. This should not be much of
>a problem with the cat-back (which IMO just changes the noise, not much
>else), but certainly is with the full system.
>BiturboS4 mailing list
>BiturboS4 at audifans.com

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