Just wanted to add my $.02. I run a 454 with 236 peanut ports in my 26' boat. I too run out of air around 4500 rpms, and want to go to around 5500 rpms.

I plan on switching to some 049 or 781 heads soon and running her until she needs a rebuild then I will make her a 496 with forged internals and then may really rev her. Oh, if I didn't run in salt water with raw water cooling (cooling water comes from body of water you are in) system, I would change to aluminum heads to save weight. I thought about putting a closed loop cooling system in, but will just stay with cast iron heads for simplicity.

Unfortunately, I don't want to loose low end grunt, which is why I want to keep the same pitch prop but just rev higher.