Built a 454 330hp stock what I did was forged crank and .030 over pistons file fit rings, balanced assembly high volume oil pump, i am running large oval port heads 2.19/1.88 valves ported and bowl blended, 8.79-1 comp, a complete crane valve-train with the 420 cam gold roller rockers 3/8 pushrods all arp bolts, running a eldelbrock performer intake and a 750 marine carb, revolution marine exhaust no mufflers and a stock thunderbolt ign. I am running a bravo 1 prop 24 pitch I have put 3.5 hours on it I finally opened it up it runs up to about 4700 rpm and thats it it falls flat on its face. I have a ton of mid-range power the boat is very quick the motor sounds good very strong. Also I am running 20w-50 oil and the motor carries 54psi of hot oil pressure. I just think it should run better than it does what does every-one else think

Which Tbolt pack are you running and what is thetop timing set at? Does it spit cough or what ever or does it just run out of power?

Phil

What fuel system are you running? What is the fuel pressure at w.o.t.?

My previous motor was the merc 330hp motor. I do believe that the Merc thunderbolt ignition module has a built-in rev limiter. Set at 4750? Sounds like with the additional power, you are running on the rev limiter.

Recommend you take off the thunderbolt module, bolt on either a Crane or MSD ignition module. The MSD does not come with a built-in rev, so you will have to purchase it separately. Good luck.

tend to agree, or just try a stiffer prop go up a couple of inches in prop and see what kind of power and top end she has... its alot safer then running without a limiter you can always change the mod later if you still feel you want the revs


keep in mind that the general rule is 1 in in pitch = 200 rpms

I'm running the stock fuel pump eldelbrock 750 marine carb it acts like it hits a wall or runs out of gas you will be running say 4200 open it wide open and it goes to about 4700 if it was up against a rev limiter wouldn't it pop or miss because it doesn't

What year? If it's a t-4 ignition, it has no rev limiter. You need to check timing at 4000 rpm and fuel pressure at wot. Also need to do a plug check at wot to see if its lean. Then try a 23 mirage to get the r's up and into range.

What boat is it in some/ most boats have a check valve to keep the fuel from going back into the tank it can resrict your flow and you run out of fuel
also what fuel seperator are you using some older stock ones have a 3/8 hose but at the filter the fittings are about 1/4 inch
I took a piece of rubber FUEL HOSE and by passed my seperator and gained 400 rpm that was only to check to see if it was the problem
then I ordersd a new seperator with larger openings

just some thoughts to check out
good luck
Darryl

the motor is 1993, wellcraft nova spyder 23ft, that is true on the fuel seperator I have a large fuel line frim the tank and 1/4 in lines coming out of it it is a mercruiser seperator

That boat might ofhad one I knoe the late 80s wellcrafts did have a check valve from the factory, it looks like a regular nipple comming off the fuel tank if you remove it and look inside you will see the ball you can take a punch or a phillips swewdriver and punch the ball out then reassemble