[s-cars] Question about compression ratios and tuning

[Mihnea Cotet]

Pistons and head combustion chambers are actually the same between 3B, AAN, 
ABY and ADU. The only difference in CR between an ADU and an AAN/ABY is the 
head gasket, the metal item is thicker and lowers CR by about .3:1. How do 
I know? The knock limits aren't at the same advance levels on a full 
RS2-equipped ABY than on an ADU. Just a few degrees, but that's enough to 
mess things up for those who do "generic" chips.

HTH,

Mihnea

At 10:36 2/02/2004 -0500, QSHIPQ at aol.com wrote:
>Bad info mike.  The 3B is 9.3 just like the AAN
>In a message dated 2/2/2004 9:23:46 AM Central Standard Time, mlped at qwest.net
>writes:
>Has anyone actually measured the combustion chamber volumes for any of these
>heads?
>
>What's the source for the information a 3B motor's default compression ratio
>is 7.8 to 1?  IMO, a difference of 1.5 vis-à-vis the AAN's 9.3 to 1 is too
>large to be accounted for by a head gasket, so that pretty much leaves
>either:
>
>(a) a substantially different piston; or
>(b) a larger head chamber.
>
>I doubt (but I don't know for a fact) it's the head chamber, so that would
>leave the piston.
>
>Anyone have a photo of the 3b piston to compare to the AAn or can they
>describe the differences?
>
>Mike
>_______________________________________________
>S-CAR-List mailing list
>S-CAR-List at audifans.com
>http://www.audifans.com/mailman/listinfo/s-car-list