The Speed Twelve is the name of a V12 engine manufactured by TVR and used in several of their cars incuding the TVR Speed 12 and TVR Cerbera Speed 12.

The engine was developed by essentially joining two Speed Six engine blocks to a common crankshaft. The completed engine displaced 7.7 liters and was originally developed for racing applications in TVR's Speed Twelve. Later on, a version was developed for the prototype of a road car to be called the Cerbera Speed Twelve.

The racing version of the engine produced approximately 675bhp with its power limited by the intake restrictors required by racing regulations. For the road-version of the engine, the restrictors were not needed so the engine was developed without them. According to reports from TVR engineers, the de-restricted engine snapped the central shaft of their 1000bhp-rated dynamometer during the bench-test. The engine's output was later estimated (conservatively) at 940bhp. When the prototype vehicle was road-tested by then-owner Peter Wheeler, he decided that the vehicle was too powerful to be practical and the project was scrapped.