I pulled my 402 BBC out to detail it out and add a proper oil pan. It was recently rebuilt by the previous owner, and looks clean on the inside. I stripped it down to a long block, and I'm about ready to start putting it back together. As far as I know it's stock. It has a Performer manifold and a Holley 650. Should I swap the intake for a single plane?

Yes....


But seriously, you really need to know how the engine was built to answer that properly. What cam?, what exhaust?, how will it be used? etc...

The Performer line of manifolds were really designed for low to mid range torque, which (IMHO) is useless in a jet. I would rather see a quality single plane or even a hybrid (like the Performer RPM Air Gap), the Performers and the Performer II's are good pieces for the tow vehicle though..

with a properly setup tune and matched pump, you should be running well into the high 4,000's as far as rpm, so I think you need to look at the whole enchilada.

GT

I'm not sure what cam is in it, I'm going to change the timing set to a double roller, hopefully there is some markings on the front of the cam. Exhaust is Harman logs. I'm not positive, but I think it was turning an A cut 4,700 rpm at WOT. I'm running in salt water, I hear that it pumps harder and loses some revs. Realistically, I don't don't see this boat surpassing 70 mph.

It depends on the salinity of the water, but yes salt water does pump harder (typically about a 100 rpm loss from fresh to salt on a stocker), but the speed will not really change just because the rpms' drop though. 

I wouldn't think you could pick up all that much with an intake change, it would be interesting to know what vacuum the engine pulls at WOT, may consider upgrading to a larger carb, but she sounds close if your tachometer is accurate. 

GT