this is what i have, help on where to go next

[Old Day Cruiser]

hello to all, I have a 24-ft day cruiser with a 290 horsepower SBC with a 280 IO and 15/19 prop. Boat weighs 4200 lbs with a stock quadrajet with thru exhaust. It goes 46 mph at 5100 rpm and at about 3000 rpm it'll go 29-30 mph. Not too sure but i have been told rpm's are too high at top speed. Was wondering what I should be at? Am planning on installing a performer rpm and a 600 Elderbrock carb. Also wondering what jetting would you recommend for the elderbrock or what changes I should do for the rpm if that is a problem? Kind of new to the boating but not hopping up cars. Thanks for any help. Old Day Cruiser.

[cfm]

Merc or Volvo engine ? Is it bone stock ?
If OEM stock Merc or Volvo, valvetrain and thus power peak is set up more for 4600-4800rpm. Prop for these rpms, no higher than 4800rpm.
You mention 280hp. You may have the GM Bowtie High Rise intake on that already. Volvo used it alot, Merc just on a few motors. If so, the RPM won't make any more power. You could install Felpro 1204 intake gaskets that block off the crossover and realize another 10-15hp (comparing engine #'s when engine is hot) but you'll have to wire the choke to open. Small price to pay for the power. Who needs chokes on warm weather boat engine's anyway ? LOL.
Take a photo of your intake and post it here - I can confirm which you have.

[centerhill condor]

also, jetting will depend on atm pressure and other variables specific to your carb, intake, cam, exhaust, etc.
You know, there is an inverse relationship between performance and reliability. The faster you go the more likely you are to break things....
sounds like a nice boat how 'bout some pics!

[Old Day Cruiser]

thanks for the replys, it's a 1983 SKV with the volvo set up. it has the old cast iron intake with the Q jet. it has a 290 hp sticker on the vavle cover.the boat is all stock. i had a pic of it awhile back on here , when i was asking for info on SKV boats. thank's again for the info. Old Day Cruiser

[TIMINATOR]

Comp cams 270H or 280H, Performer Airgap intake, tru-roller timing set, route the exhaust out the transom =10+ MPH gain. We've done it many times. TIMINATOR

[Havasu Hangin']

Comp cams 270H or 280H, Performer Airgap intake, tru-roller timing set, route the exhaust out the transom =10+ MPH gain. We've done it many times. TIMINATOR
Plus a new prop.
I would also ditch that crappy stock Volvo distributor (I think I went to buy a cap for mine once and it was listed under "farm equipment"...lol) and cast iron Volvo exhaust manifolds.

[TIMINATOR]

Forgot the 750 Edelbrock carb. TIMINATOR

[Old Day Cruiser]

so 4800 is the top rpm i should run with the stock vavle springs. if i install hipo springs would i be better off and be able to run higher rpm's? another question i have is. i have always read to use a airgap or rpm performer manifold. i understand about better air/gas flow and a cooler air/gas charge to the cyl's. but these manifolds are good up to 6500 rpm's. so what good is it to put a 6500 rpm manlfold on a 4800 rpm motor? is it just the flow and cooler charge? or is there more to it? i have my prop in the shop and having it cuped. they say it will bring down the rpm's 3 to 400 rpm's and up mph 2 or 3 mph. does this sound right? the boats top rpm are 5100 at full throttle. thank's again for all the info. Old Day Cruiser

[cfm]

Engine with that cam is about done there too, not just the springs.
That rpm is what the intake is generically rated for. They have to put something in there. LOL. The Bowtie intake is killer. I use'm all the time.
To reduce heat I suggested the Fel-pro intake gaskets (#1204) that block off the exhaust crossover. Exhaust gases are very hot and get an intake cooking ! Don't forget to wire the choke open if quadrajet or properly remove if Holley.