Re: S4 20v vs S2 10v

[Dan Bocek <dan@di.com>]

> The S4 uses (dave L?) a bleed at the compressor that maintains the boost
> pressure between shifts, vs the RS2/stock turbos do not have this feature.

Actually, this is called a compressor bypass valve, and you can get 'em 
right from audi and upgrade a non-equiped car.  All it does is re-route the 
air from the high pressure side of the turbo to the low pressure side 
when it detects that there is a vacuum present in the manifold (i.e. 
closed throttle conditions).  This prevents the backpressure wave that 
happens in cars not so equipped, which has the effect of stalling the 
compressor blades of the turbo, hence making it take longer for boost to 
come on the next time you step on it.

If you really want something special, Sport Wheels has managed to get 
ahold of some of the compressor bypass valves used on the Sport Quattro, 
which are capable of handling higher airflow rates.  I've got here, and 
am just waiting for the rest of my parts to come in so I can try it out 
on my URq.

                                                         Dan Bocek
                                                         dan@di.com