I have basically stock 1980's 330hp with cast iron intakes and stock carbs. Peanut port heads basically. My manifolds are in rough shape, so I bought some oval port aluminum manifolds. They're larger oval ports than my heads. Am I going to have any problem running large oval port manifolds on peanut port heads? I also bought Holley 750 marine carbs to run on the new manifolds. I have Stainless Marine Exhaust too. If not what gaskets should I run? I recent was told not to use Felpro because marine engines dont run hot enough for the Flepro gaskets to seal.

Thanks
Bill

It will work, it just won't flow very well. When you bought the intake did you tell them you had peanut ports? Small oval intakes are available. When I ordered my Holley MPI kit they asked me if I had small or large ovals, at that time I had peanut ports. When I switched over to Large Oval heads I just did a little port work to do the gasket match.

they will wok ok in a heavy boat..I use Mr Gasket oval port gaskets...

I bought them with intention of swapping the heads too. But I'm going to wait on the heads now and I need the mani's swapped. I'm afraid that one of my stock ones is leaking.
Do you think the boat will run worse than with the stock ones, provided the stock ones weren't leaking?

And EZ thanks for gaskets choice. That was the 2nd vote for Mr. Gaskets.

Thanks
Bill

You're going to pick up some turbulence going from the large oval port on the intake to the smaller port on the head. Basically the flow is going to crash into the smaller wall (or lip) of the head, bounce off, run into itself, and end up getting forced down into the head. That turbulence is going to flow less than a smooth transition from a matching intake/head set.

That said, the power loss shouldn't be more than 10-15hp., or 1-2mph. I really don't think you'll notice it. If you did have some sort of vacuum leak or some other problem you may even pick up some HP with the new installation.

If you still have everything apart I would try to pick up some 781 casting (preferable) or 049 casting heads cheap. I bought a pair for under $500 with new valve jobs and guides. With the larger oval heads, intake and new carb you should increase your HP and your upper RPM band.