<VV> Compression ratio for 140HP Engine

[Craig Nicol]

    <snip>      Can anyone tell me about OEM specs on combustion chamber
volume for 140 heads? Also cylinder seating surface depth in inches for
same, and anything on squish or quench area  to piston top clearance for
optimum turbulence with out risk of detonation using pump gas (91 Octane
max). My performance book says around 0.025" is optimum, although, this book
was published many years ago when we had higher octane fuels (including
leaded fuels) at the pump. I don't know what is safe for 91 octane unleaded
and a Corvair air cooled engine with 140 heads. I would also like to hear
about solutions for detonation in these air cooled engines today? What is
acceptable compression ratio for pump gas with these engines? Thanks. John
<unsnip>

 

A typical 140 head (1965 3856728) is listed with a combustion chamber cc of
49.277cc and a squish of .62".  I have modified many 140 engines to a squish
of .032" (copper head gasket) and 49-50cc (depending on bore diameter.  This
mod, due to the improved fuel mixing (squish/tumble) and more compact
chamber, improves power and greatly improves resistance to spark knock. Once
I took a 110 to 10:1 with this same approach and it worked well too but did
knock once and a while. 

Craig Nicol