I got the same problem, 4 different carbs and 4 different props and it still only turns 4900... 454-425 crate motor

Just because 5600rpms is what the cam is designed to run at for max rpm, doesn't mean it will in your boat. Your heavy boat needs torque and your engines are probably starting to fall off in torque too much at about 4900rpms. Go down 2" in pitch on your props.

I agree, a 750cfm is on the small side for 496ci.

rpm air gap
 

496 ci, rpm air gap intake Motors pull way to good from 3800 4900 if it was props it would take waaaay longer to get there.iIt will accelerate from say 40mph about 3800k to 60mph 5k inabout 3or 4 sec. This boat with stock 330s and 21 pitch would run 5300 5400 and around 52 55 . Ive dynoed the motors and there double the trq. almost double hp.

I dynoed them and yes trq. is starting to fall but its still over 500 ft pnds peek is around 4k at 610 way more than a stock 330 merc. If I go down in pitch I wont be as fast as stock 330 if Im thinkin right

What props are you running now????

23 mirages

My mechanic and also the company that sold me the motor said that I would be able to put my intake off the 420hp on the 330hp. Just wandering what kind of results I'm gonna see. I could get 60-62 in a 88 240 sport with the 420, but its really tired ( mechanic said probably only puttin out 325hp). I'm hopin to see the same if I take my setup off the 420 and put it on the 330, with a few adjustments. Anybody do anything similar to this and what were the results.

Looking back at another thread

You need some aftermarket exhaust!!!!!!!!! The engine can't breath.

Your rpms and prop change indicate that you are making same power at 4900rpms now that you were before teh engine mods.

yes you can put a rect port intake on a (I still call them oval) heads, but the port mismatch is going to cost you !

What do you mean its gonna cost me? Do you mean the engine itself is not going to run as well as it would with matched ports? And if I'm correct the ports on the 330 are considered oval, they are just the small oval and there is also large oval ports (maybe this is wrong, I'm still learnin. Thats why I'm posting).