The staff at Hot Rod magazine got the chance to dyno test a one-off Chevy 427 Mystery Motor built by the legendary Smokey Yunick in 1963. Although the 427 isn’t officially part of the Mark IV family, this Mark II engine is essentially the predecessor to the Rat motor, which came along in 1965. This experimental “Mystery Motor” was basically a modified version of Chevy’s W-series engine. It featured more conventional wedge-shaped combustion chambers and larger, canted valves compared to the original W-blocks. The top secret engine was used inside Junior Johnson’s Chevy at the Daytona 500 and was the forefather of the famous Rat motor.
Depending on who you ask, anywhere from 17 to 50 Mark II 427s were made. These engines are rare and highly historic–and Hot Rod got to open one up and then dyno test it. Click over to Hot Rod to get the details on the experience, including tons of photos and all-important dyno numbers.