[s-cars] Question about compression ratios and tuning

[Peter Schulz]

James:

I think that you also need to take into the account that the engines are 
turboed and stock spec'ed for different size turbos.
Stock MC to had the K26? and stock 3b/AAN had the K24.


-Peter

At 10:28 AM 2/2/2004, James Bufkin wrote:
>My mistake,
>I was stating the older 10V spec for a 1991 200.
>Still my question stands.  What benefits and disadvantages occur when 
>mating an ECU designed around 9.3:1 CR to a motor with a CR of 7:1?
>
>I think reliability would be high, but power would be down.  How much down?
>
>James
>
>>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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