[tubman]

Here's what the internet said :

A "Ricardo" type cylinder head had the spark plug and the main combustion chamber placed over the valves of the ell type head engine. The volume of this chamber was considerably larger than the small clearance space provided above the piston and the transition throat that connected this space to the main combustion chamber. As the piston approached the top of its compression stroke, the fresh air/fuel charge was squeezed, or squished, through the ever narrowing transition throat. The rush of the increasingly dense air/fuel charge through this transition throat created considerable turbulence in the combustion chamber. When the spark plug ignited the turbulent mixture, the flame front spread fast resulting in quicker, smoother, more complete burn of the fuel, reducing spark plug fouling and lowering the exhaust temperature. This resulted in more, smoother, power, better fuel economy and was less susceptible to detonation than the slower burn of a relatively stagnant mixture of a main combustion chamber above the piston in previous cylinder head designs.

This describes a flathead Ford combustion chamber to me, and explains why it is so important to have minimum clearance over the piston top and the head, which most of us try to achieve.