Exhaust manifolds

There was some discussion on another boating forum about the advantages of switching from the older log style manifolds on the 7.4 motors to the center rise style with 4" elbows. Was wondering if anyone has done the switch and seen any honest gains in H.P. or mileage. I would think with the peanut port heads on these motors gains would be minimum for the expense.

did it years ago....and opened the rest of the exhaust system as well.

Biggest changed noted was improved acceleration...it will throw you to the transom if you aren't holding on...

That must have been on your hotrod Mercs Lol!! I don't think these Crusaders have that in em...

the only high performance part in the whole rebuild was the ignition modules we used - they provided 20 degrees of advance, all in by 3200 rpm....we actually lowered the compression a bit due to the pistons that were available....

the huge reduction in back pressure really let the engine breath much better.

Overall the fuel consumption improved a bunch.....but we didn't have the luxury of time to make detailed measurements after each mod.....we just used the floscan and a vacuum gauge.

Going from memory, the biggest economy improvements were made in the carb tuning......getting the correct power piston springs was probably the best. there may be a few more gal/hr to be saved with further tuning though we haven't obtained all the parts yet...