Have a 350 engine question concerning exhaust. I installed two 350 gm engines, 80-86 vintage rebuilds, into my silverton. In 5 years, I've gone through 3 sets of exhaust manifolds and 4 sets of risers, changing them almost every year. I sea water cool the manifolds but now will fresh water cool them. The reason for the replacements is I keep having leaks between the Barr manifold and Barr risers, at the exhaust/water jacket area. It constantly stains the manifolds leaking onto the heads when they leak, meaning outboard leaks have started. Now I have hydrolock damage, and took the heads off. I torque the riser bolts at install and after running. (hot). I tried using the gaskets dry, then with mercruiser sealant, as per the parts man's recommendation. He had mentioned possibly having a 3" riser outlet, that there may be too much back pressure. I personally don't think so. I myself am thinking maybe my timing is a little too retarded, raising the exhaust temp and burning the gaskets. I am installing fresh water cooling for the manifolds and am hoping this is the answer. Any takes on this out there? Thanks.
