convincor

Would it be worth it to change cam, carb and intake on a otherwise stock 330hp merc??
Was thinking about an "air gap intake", "barry grant" sea demon carb and not sure what would be a good cam.
Will be running "stainless marine" manifolds.

The boats a 25' checkmate, bravo drive with a 23p mirage plus.
Last year it ran about 60 on speedo at 42-4300 rpm. It also had corsa silencers which have now been changed to strait thru tips.
What should I expect with these changes???
What size carb??

mcollinstn

Sure. You'll need a longer duration camshaft but stick with lower lift figures than what you'd use with rectangle port heads.

A cam around [email protected] and .535 lift with 112-114 degree lobe center.

If you plan to take the heads off, have the valves unshrouded and some bowl work done.

Don't go nuts with anything else - it is a cast crank, cast piston, peanut port 454...

I'd guess you'll see 40-50 horsepower (you'll need to prop for 4900 rpm).

convincor

what would you say to edelbrock performer rpm heads??
They make them for marine with 2.25 intake, 1.88 exhaust valves.
For a aluminium head, there very resonable. Would this be to much for my bottom end??

formula31

If those are the 110 cc combustion chamber, oval port heads, they would give the motor a considerable kick in the pants with the right cam. If the lower end is solid and true, it might be OK. Lots of ifs. Id at least put new bearings and ARP rod bolts in it and check everything closely.

mcollinstn

Don't turn that motor over 5000 rpm.
Crank and rods will be much happier.

Don't run that motor into detonation - the cast pistons can't take the shock loading.

Don't expect more than 400 hp out of that motor or you'll be tempting breakage.

How much do you want to do to it? Are you planning on opening up the bottom end (bearings and rod bolts) or are you looking for bolt-ons (top end pieces)?

Heads will wake it up. Will put it around 400 hp with the cam mentioned. Your money, not mine.

blown1500

I pretty much agree with mcollinstn. If you are not going to do anything with the heads, you are pretty much wasting time and money. Almost any aftermarket head is major improvement over the stocker. If aluminum is over your budget, try Merlin oval port. That might be my first choice. If you stay out of detonation and don't turn it more than 5,000, the rod bolts will not break and the postons will live. The lower the rpm, though, the better it will like it. Almost any detonation will explode the motor.

convincor

want to do bolt on parts this year. reason for thinking about heads. want to do 502 bottom end next winter. can't do it all now.
what size carb ???

mcollinstn

aftermarket heads will benefit from higher lift cam than your peanut heads. If you plan to go 502, this will require more cam as well... SO - do you start adding your "502" cam now or do you run a cast crank 454 cam now?

Whatcha wantin to do? The 502 cam will soften your bottom end up a bit. Will still be pulling WAY past 5000 rpm (which you must not exceed)...

Let us know what you really want and then we make a "menu" and calendar.

mcollinstn

750 cfm for the 454 described above.
How you flavor the "future" 502 will affect the carb choice for it, though (800 for a 425 hp 502, 850 for a 500 hp 502).

Jayl13

my advice (done this two times)
dont worry about HP numbers
Go for TORQUE increases
HP does not mean piss
Torque does
these engines were built for TORQUE not for HP
just keep that in the back of your mind while rebuilding
Also I went with stock oval heads on mine, worthless
either go rectangle or dont bother with heads
did not do ****
I went from stock 330
to the following
large oval heads
RPM performer intake, holley 800
Comp Cams 224 230 515 521 110 LSA
Hypereutectic pistons and increased compression to 9.5:1
Best dyno so far with 10 degrees of idle advance is 388 HP at 5200 but the torque numbers were in the 500's
which means you have enough torque to turn some major props
was I pleased with my rebuild?
NO
My combo worked for ****
I hope you have a better time picking a combo that works better than mine
As I figure it, I wasted about 10 grand in this rebuild of my pair
Hope you do better
Jason