[s-cars] Question about compression ratios and tuning

[QSHIPQ at aol.com]

Further trivia...  The US WX block was 7:1 CR, but all audisport motors used 
either higher or lower.  The  A1/A2 cars were 6.3/6.5 respectively, the SQ 
came out at 8.0 and it's displacement was 2142, not the 2144 found in the WX or 
the 2145 (A1) or 2133 (A2). Ah those 1.4 equivelency factors confused even 
those keeping track...

To answer your question James - What is common on the 20vt motor (9.3:1) is 
to pop them down to 8.5:1, which yields a massive increase in torque in the 
midrange.  I suspect you would lose a bit of that on a 7:1 motor (if that's 
indeed what you have), but the bottom line really is the lower the compression the 
higher the boost levels (effective compression levels) can be.  Most of the 
German tuners have gone with the 8.5:1 as the optimal for all around 
performance.  I've driven a couple of these, and completely agree.  Tho really, the 9.3:1 
CR motors do pretty well if the temperatures (IC, engine, EGT) are kept at 
reasonable levels.

Will this work?  Sure it will, but most likely a dip that low in compression 
will require that some dyno tuning to make it work.  Even then, unless you are 
really set on the lower 2100cc blocks, the 2226 or higher is the better way 
to go.  Certainly audisport was constrained (and got equivelencies right to 
2999cc) by the 1.4 factor, tho I personally see very little desire for it if you 
have the choice.  For piston speed equivelents you can just do bore, for big 
dogging, the 2.5conversion with 8.5:1 CR is probably getting the most out of 
the 20vt configuration.

HTH

Scott Justusson
QSHIPQ Performance Tuning


In a message dated 2/2/2004 8:45:17 AM Central Standard Time, pcschulz at c
omcast.net writes:
At 08:59 AM 2/2/2004, James Bufkin wrote:
>3B engines have a default compression ratio of 7.8:1 with a displacement 
>of 2226ccs.
>AANs have a CR of 9.3:1 with a displacement of 2226ccs
>S1 blocks have a CR of 7:1 with a displacement of 2100ccs.
>
>What effect would using a 3B or AAN ECU in conjunction have on an S1 
>block?   What power band characteristics would such an engine have?
>
>James
>Austin TX
>
>_______________________________________________
>S-CAR-List mailing list
>S-CAR-List at audifans.com
>http://www.audifans.com/mailman/listinfo/s-car-list


James:

the 3B engine ALSO has a compression ration of 9:3:1

http://members.aol.com/c1j1miller/


-Peter