I run a 98 Marine Power 454MPI in a Jet boat. The motor is a gen VI 390hp with 200 hours on it. With the jet pump, the cruise is just under 3000 and WOT is 3600 at 2000ft elevation. I have been looking at a couple upgrade levels and wanted some input based on others'experience.

Option 1: 50hp increase, trying to gain 400-500rpm. 496HO cam with an ECU reprogram? Est cost $1k

option 2: 100hp increase, this would allow me to run the next size up impellar at 4000rpm. Cam upgrade, aluminum heads, ECU re-program. Est cost $3k

Any advice out there or another road I should consider? I did not list exhaust headers as they seem cost prohibitive, maybe a better flowing factory manifold from say a 496? I am trying to keep this upgrade as inexpensive as possible.

Supercharger

Do some searching on the site, trying to get any decent HP out of this engine just doesn't happen without spending some real bucks.

To get any power, you have to change the cam, which is ok, but you also have to change the exhaust, and then the restriction is in the intake, so by the time you are done, you have replaced the whole upper half before you have even touched the computer.

Call Mark at Performance Marine, he is a wiz when it comes to programing the computers, and he will tell you what you can and can't do with these motors. Been there, done that, even after reading the other forums, thinking I could make it work, all I wanted was 100 hp. Didn't happen.

That engine needs to reach a minimum 4400 WOT rpm. It is currently overloaded. I'm surprised that you have made it to 200 hours without roasting the heads.

change impeller size?

What pump are you running? 3600rpm isn't even close to enough RPM for WOT. There's probably a lot of performance to be had from dialing in your current combo..

Its a jet boat. They have impellers instead of propellers.

X2........You should be spinning at least 4600rpms at WOT.

X3
At least 4600

Not sure where you live but I would look for someone in your area familiar with jets. 3600 rpm is a cruising rpm even with that engine. There is something else going on causing your engine to only turn 3600. Also try the jetboat section on Performanceboats.com lots of good advice for Jets over there.