Thread:

intake manifold help please

hello alexi,,, I changed my heads and intake manifold on my mercruiser 7.4 from peanut ports to big valve large oval ports I also am putting an aluminum zz502 intake manifold on the engine, which will convert me to a square bore carb instead of the original Q jet, my question is should I leave the under the carb exhaust cross over open or use the aftermarket type intake gasket set that has the tin block off plates? my set up is a 228/238 duration at 50, 540 lift hydraulic flat tappet, 9 to 1 compression, crate motor zz502 dual plane intake manifold, edelbrock 750 carb with electric choke, nicer stainless marine brand exhaust manifolds with swept back through hull big tub risers, it's all in a twin engine 31' offshore, I am redoing both engines top end, bigger heads, bigger cams, roller rockers, aluminum intakes, edelbrock carbs, so with this set up should I block the heat riser passage or not? also how much should expect to gain in HP with all these drastic changes over a gutless peanut head 330hp engine I started out with?

Yes. Block off crossover. I would think 425-450 H.P.

I would use the block gaskets. They have a metal insert. The engine power range will likely be best 4-5000 rpm and 420-500 is Likely a legit goal!

thanks guys for the info much appreciated! ronnie

Any time