[s-cars] Question about compression ratios and tuning

[Mihnea Cotet]

According to Audi, a 3B has 9.3:1 CR, just like an AAN. According to my 
experience, an AAN with metal head gasket has 9.0:1 CR, just
like an ADU (RS2 motor).

I haven't been able so far to say that a 3B has 7.8:1 CR, this would mean 
that the knock limits of the motor are much further than on an AAN, and 
this just isn't the case...

HTH,

Mihnea

At 08:23 2/02/2004 -0700, M Pederson wrote:
>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
>
>-----Original Message-----
>From: s-car-list On Behalf Of James Bufkin
>
>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
>
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