Squish Angle

I usually design domes with the squish area parallel or very close to it for racing applications. Increasing the squish angle slightly (+1 to +3 degrees more than the piston crown radius) makes the shape a little bit more forgiving to fuel octane (if it varies a bit) and less prone to detonation. Parallel designs carry less charge in the squish area therefor more of the fresh mixture can contribute to making power. Designs with the squish area set between 4 and 20 degrees (or more) greater than the piston crown radius usually produces a powerband that hits softer and may allow for greater over-rev. It may also be kinder to the piston and bore due to the "easier" combustion process.