kornegle

I used the Performer intake not the RPM air gap because I wanted to keep my Quadrajunk carb and the RPM Air Gap only accepts square bore carbs. Mine was a 260 Mercruiser (230HP at the prop). Your Vortec heads will not accept the lift of the cam you selected and I would be concerned about reversion as well with that cam. You will have to cut the valve guides down so the retainers don't hit the stem seals and then cut the valve pockets deeper, or use expensive Beehive springs to accept the lift. I used GM Z 28 valve springs and only used the outer springs since the inners did not fit and the harmonics are fine up to 5000 rpm without the inners. They say the RPM air gap and 1.6 roller rockers (you have to drill the pushrod holes out with 1.6 and that is why I used 1.5 roller rockers) combined are close to 36 HP. Your engine year I believe had 280 - 300 HP with a 4 barrel. The heads I replaced had 76 cc chambers and I kept the stock pistons so my compression was around 9.7:1 when I installed the lower cc Vortec heads. I ran 89 octane and 31* total timing to be safe.

kornegle

One more thing, you could do some chamber work or pocket porting on your Vortecs to help out a bit, or buy the GM performance Vortecs with the larger intake runners and larger valves but I think they are close to $1000 a set today. I also got rid of the exhaust bellows and installed an exhaust tube but I think you have thru transom exhaust so that should help you out, I had stock thru prop exhaust. I could not even tell mine had a cam in it when it idled but the one you want, will have a noticeable chop at idle but again I would be concerned about reversion and go down a bit in cam size. Mine was awesome on fuel consumption, had excellent mid range and good top end since I only turned it 5000 rpm. If that is all you are going to turn it, I would stay with the cam I used or one size up. If you want to turn it higher and trust your bottom end, perhaps the larger cam is OK if you do not get reversion and don't mind doing the machine work and Beehive springs to your heads. I had MSD coil, wires and stock Thunderbolt ignition and distributor. I upgraded to a double roller timing chain and degreed the cam in.

Wharf Rat 1

I too had a 350 in a Formula . 300 hp 50-55mph I swapped it out and got a big block 400 hp 60-65 it's the torque that made the diff. my boat is 4200lbs dry. You need something that will get that boat up and going. It was suggested that I go to the 383 stroker. So glad that I didn't.

94sylvan

I struggled with a 1409 600 cfm on a similar setup both 350 and 383 displacements. Tried about 20 different metering rod and jet combos and always fat off idle and leaned out on top end. Went through fuel lines, pumps, etc. never found the answer. Went to a 780 vac secondary Holley, fuel consumption was cut by a third, power was up, (2mph gain first time bolting it on) and AFR was good across the board. In my experience with a boat just slightly lighter than yours 20hp = 1 mph.

Baja Rooster

iTrader: (1)

It’s been a long minute since I’ve played with a sbc but what’s the downside of a 383?

Dylon333

Not so much that there’a a down side, just more money then I’ll looking to spend on this boat, and the 383 will over power the out drive and I don’t want to be worried about killing drives all the time

Blueabyss

I dont see a lot of money difference in a 383 vs 350 if your trying to make 350 HP. The 383 will not be what breaks the drive on that boat. Your throttle hand might.

Chris

Dylon333

I can do a cam and intake and carb for less then 2k. 383 going to be 5k

speicher lane

So, upgrade your top end and see where you get in HP and MPH for your 2K... if it's not where you want to be, you are obviously into upgrading the bottom end.
There is no such thing as cheap speed or HP - you have to pay somewhere - initially, or parts/fuel/reliability at every change from stock.

Dylon333

That is kind of my plan was just hoping someone would know what kind of power a setup like that would make