The car engine revs faster due to a flywheel (low rotating mass) being fitted. These engines do have more advanced timing. I have converted a Thunder Tiger .12 buggy engine to airplane use. I basically turned the heat sink head down on a lathe to reduce the height. It now has a head two fins high instead of eight fins high. This engine spins up to 18,000RPM with a 7X6 prop. This is low compared to using a flywheel spinning at 28,000 - 30,000 RPM.