I was wondering if its possible to upgrade the 16H engine to some more cc
yust as the M20 with a other ( M21) crank or piston ? So there is some more
power.
The Big 4 engine is physically taller than the 16H and WD Big 4s are a later pattern.
You'll struggle to find a 1937 pattern Big 4 crank and top end and they are a very tight fit in the 'short' WD frame.
Most 16H barrels can be bored to 82mm to take a Big 4 piston if you can find one (some early cylinders don't have enough meat at the base). Compression ratio can be raised to make them a little more lively.
I find mine quite fast enough for the brakes to be honest.