[s-cars] Re: RS2 TURBOCHARGER CALCULATIONS - LONG - definitive answers

[James Bufkin]

I'd like to interject some of my own amateur experience and conclusions.
I've spent a great deal of energy researching what turbo and manifold would 
be appropriate for my car and have talked with Lehmann about it as well as 
many people here in the United States.  I've also looked at the maps (RS2, 
etc.) and have come to the same conculsions that Mihnea has.  The RS2 seems 
limited at the upper RPMs at high boost.  Limited in its ability to supply 
air without overheating and its ability to flow the air out of the exhaust 
without a rise in EGTs.   Hence the reason why Audi ran K27s on All their 
I5 race machines.   That is huge evidence.   Audisport could have made any 
K26 they wanted in the 1980s.  They had custom runs of only 15 turbos made 
and chose to use exclusively K27s.   Surely if those guys felt the K26 was 
the way to go they would have used one in their race cars.    Lehmann is 
quite adamant about it for high HP cars and anything that will race or see 
extensive track use.    I've gone against his advice a bit and opted to use 
the #7 K27 instead of the #9 K27 hotside.  Now perhaps his decisions are 
based more on controlling EGTs and DRs for prolonged high HP production and 
not drivability.  But if we're talking about making HP to get speed then 
drivability takes a backseat.

I would however recommend an RS2 for any street car that is designed to 
make 350 Crank HP or so.  Like the original RS2.   Going beyond that is 
wishful and/or time limited for short durations of high HP in optimum 
environments.

James E. Bufkin, P.E.
Bufkin Design and Engineering, inc.
2309 West 8th Street
Austin, Texas 78703
512-236-8070
fax 512-480-5927