[s-cars] power loss question

[Paul Heneghan]

>From Scott Mockry's site:

'The 1992-96 Audi S4 in overboost mode will have boost set to about 2.15
bar absolute. The actual boost produced will vary depending on engine
RPM, air temperature, fuel quality, and altitude.'

Note: the overboost here is not the catastrophic gross overboost
condition that causes the ECU to shut down the fuel pump and enter
limp-home condition, it is a mild overboost deliberately produced by the
ECU under certain conditions.

Is this what you're seeing?  It's quite pronounced on mine - if you do
WOT, the boost and power build rapidly as you approach 2000rpm and then
fall off a little somewhere between 3000 and 4000.  One the Avant, I see
a peak reading of 2.0 dropping down to 1.8, on the saloon, I see a peak
of 2.2 dropping down to 2.0.  These are not accurate figures as they
come from the notoriously inaccurate multifunction-computer boost gauge.

If you don't do WOT, but feed in the power gently then you don't notice
this mild overboost.

You probably all knew all this already, but I wasted a few days looking
for a hose leak that didn't exist because of this slight power reduction
at higher revs.  Anyone know why it's there - engine longevity perhaps?

Paul

From: Elijahallen92 at aol.com
Subject: [s-cars] power loss question

>Hi,
> I have been thinking about getting the car on a dyno soon and am not
sure 
>what rpm they start at but if I am in forth gear and start at say 2000
rpm's, I 
>floor it, the car gets to 3000 or so and builds boost, by 3500 I'm at
full 
>boost but right after I hit full boost power cuts way off and boost
drops. Its 
>not a violent shut off like overboost where it feels like you just left
the 
>tranny in the road but more like if you went from full throttle to half
throttle. 
>The only time it does it is if I floor it from a very low rpm like that
which 
>is never but I am worried that on the dyno I will have a problem with
this. 
>Any Idea what/ why this happens? Thanks,
>
>Elijah


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