HOME and how to join Forum Open Area General Scott topics squished heads Re: Re: squished heads

#12942
Stan Thomas
Participant

I take your point Brian, but surely a cylinder head combustion space shaped to the profile of the piston (to raise the compression ratio) would not have combustion volume when correctly measured of 86cc?? notwithstanding such a combustion shape would reduce the volume compared to a standard profile, however measured.

I suspect Richard has mererly filled the combustion chamber of the head with it removed from the engine, as 74cc sounds about right when measured as a total space – which of course does not allow for the dispacement of the deflector.

Combustion volume can only be measured with the head in situ and with the piston at the top of the stroke, preferably with the engine removed, or at least with the bike jacked up at the front!!

Why?

Because the standard cylinder head combustion space is composed of two hemespheres of differing radii, and filling the combustion chamber to measure the volume with both wheels on the ground and the cylinders sloping forward may result in a trapped air-space and give a false reading. Trust me, I’ve been down that road – and got the tee shirt .