A two-stroke engine's an internal combustion engine which completes the thermodynamic cycle in two movements of the piston (compared to twice that number for a four-stroke engine). This increased efficiency's accomplished by using the beginning of the compression stroke and the end of the combustion stroke to simultaneously perform the intake and exhaust (or scavenging) functions. In this way two-stroke engines often provide strikingly high specific power. Petrol (spark ignition) versions are pa… (More on Two-stroke)