 Vendors of model engines rate size in terms of engine displacement.Common sizes range from as small as 0.01 cubic inch (in3) to over 1.0 in3 (0.16 cc–16 cc).Under ideal conditions, the smallest .01 engines can turn a propeller at speeds over 30,000 rpm, while the typical larger (.40-.60 cubic inch) engine will turn at 10–14,000 rpm.