Mild upgrades to a 1989 330hp 7.4. It runs 59MPH on GPS turning 4600RPM, Upgrades include, edelbrock performer intake manifold matched to an edelbrock 750CFM marine carb,IMCO powerflow exhaust. I am turning a 21 pitch Stainless steel three blade. The thing has all kinds of mid-range power, Comes on plane instantly then hits a wall at 4600RPM. Guessing cam and head restrictions, My question is will i be able to turn a 4 blade with a 22" pitch and get some more top speed Or am i already maxed out considering my low WOT RPM?

Anyone?????

What kind of boat? I think 4600 is pretty near the max rpm recomendation. The only way to find out if a different prop will give you more speed is to try it. Props are a black science if you ask me.

Its in a 1989 Chaparral 236 SX.

Are you running a stock cam set up?Check your timing and plugs also With a non mag motor i wouldn't push it more than 4700r's, your gonna get more top end from a 3 blade , i would try a 23 pitch labbed 3 blade for the heck of it

Your boat will not likely be faster with a 4 blade vs. the 3 blade.
I had a 1989 24' Pantera with a 330 in it and did turn that engine up to 4900rpm. I don't think it really made much more power though.
Cam and head work is really the only way to see any significant gains.

I Was Turning A 23p Mirage On My 7.4 330hp To 4900rpm On A 1991 21 Scarab 3300LBS 59.9MPH.TO SEE ANY GAIN YOU NEED TO CHANGE THE CAM AND HEADS AT LEAST THAT WAS THE ONLY WAY I COULD DO IT.

Is it true that earlier 330's (1982) had better heads? I've got an intake and carb, going to buy better exhaust, unless it's all for naught. I'm not pulling the heads or anything internal. I leave it as is if it has to come apart.