Just as an 'interesting' aside...
I used to do a bit with Talbot Avengers and Sunbeams - the 1.6 pushrod engine has half the combustion chamber in the cylinder.. the piston stops well short of the block deck, absolutely no squish area whatsoever! They can make fair power (in their day anyway) but the ignition advance curve to achieve it is wild - ours had max advance of 48 degrees!