Sticking with the inline 6 in the 20'

[Fr. Frank]

Mercruiser built a 250 hp version of the 250ci inline six sterndrive from 1970 to 1972 or so by adding a 4bbl carb, changing the camshaft, and using through-hull exhaust. (Single exhaust, though). They didn't even have to change the manifold as it's already opened up for a 4bbl.

You won't find it listed on any parts catalogue because it was never openly available to the public, and was always considered a non-production motor.

Crower makes a great cam for this motor in marine use, the Crower Compu-Pro Performance Level 3 Camshafts #03242. It's got 262/.478 intake and 272/.490 exhaust. With the right carb and ignition this motor can make 275 hp at 4500 rpm with this cam. This is the cam setup used in a lot of circle track racing where the motor is constantly running at 3000-4500 rpms.