log vs center rise exhaust
 

I am going to be replacing my 350/260 hp this fall in my c/c scorpion 230 with a 350/350 hp. The boat weighs about 3500 and has a cobra outdrive. My question is, is it worth changing from the log style manifold with thru hulls to center rise with thru hulls. Am I going to have a noticable diff. My logs are only 2 yrs old and are in good shape, so should I just wait untill I have toreplace them. Thanks

There isn't much difference in performance between the OMC "Log" and the OMC "Center Riser" manifolds (1-2 horsepower).

Suprisingly (because OMC engineers were idiots) they realized that the best performing exhaust manifolds for a Chevy V8 divided cylinders 5 and 7 on the Port side and 4 and 8 on the Starboard side. When they designed the OMC "log style" manifold they moved the riser forward enough on the top of the manifold to accomplish this division. The riser is centered between and divides cylinders 5 and 7 and isolates cylinder 8.

A true "log" manifold has the exhaust outlet at the end like the (stupidly designed) Mercruiser "Log" manifold.
Dennis Moore

Thank you for the information on the manifolds. I won't worry about them until I have to change them. When that time comes should I consider the mercruiser center rise over the omc or does it not matter.