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.
__________________
Common Sense is learning from your mistakes. Wisdom is learning from the other guy's mistakes.
Fr. Frank says:
Jesus liked fishing, too. He even walked on water to get to the boat!
Currently without a SeaCraft 
(2) Pompano 12' fishing kayaks
'73 Cobia 18' prototype "Casting Skiff", 70hp Mercury
|