What kind of power do you think your motors make? And what is your compression ratio?

Griff answered the "why" as to why you can't run over 10-1 on a marine motor.

Jason, if you want to make your rebuild worth doing, you really are going to have to upgrade your heads. The $300-600 you'll spend on 781s or 049s will be well worth it in the end. There is at least 3 pair of those peanut port heads in my area on CL right now for $50-100 a pair. You really can't give them away, that's how horrible they are.

Drag motors and high performance boat motors are worlds apart. Give Bob Madera a call and let the Marine Performance professional guide you thru the maze of BS that is sometimes projected here on OSO. Thank god that you didn't start this thread over on Speed Hump.

happend to take one of my engines apart and came up with a good set of 781,s figured since i had that set id find another i picked another set up as well so i know have the 781,s going on them one set needs some brass liners shoved in em havent messed with cams yet as i had to figure out spring od,s installed heights etc before i ordered anything.. yes i know drag car and boat engines are different.. just saying im familar with engines

jayson,with all due respect,griff and mild thunder gave you good advice,im glad to see you are listening and dumping the peanut port heads,the truth is the stock exhaust manifolds will cause reversion with either of the cams you asked about,but with a set of decent exhaust manifolds,and your new heads,either cam will work good,i think you are on the right track,and you are right,you can build a decent engine for not a ton of money,as long as you keep your goals realistic.good luck with your project,i am sure it will turn out well.

9-1comp and it made 407hp at 5200rpm on the dyno.

No reversion bc Your cams are very mild. Not much hotter than a stock 454 mag flat tapper cam. A exhaust change, cam change, would wake the engines up.

Yep, thats why I picked that Isky cam when I was building my engine. I didn't have the money to build a new engine and another 2k for exhaust. The engine is basicly a 330hp bottom end with a Magnum top end (188 heads, small cam, 1.7 roller rockers).

I used stock exhaust manifolds with Merc. 420's for a while. The 420 cam is 226/236 @ .050 and about .560 lift. I had no problems with reversion but I wouldn't go any bigger. With close to 10 to 1 compression and iron heads, I would only run 93 octane and a perfect tune. Good luck. BTW, the cam used to be made by Crane.

Thanks, I was going to post that I think you can use a 420 cam with stock exhaust. The Merc 420 exhaust is nothing special. It's basically a stock exhaust with a slightly bigger riser and a stainless exit tube. I can't see why it would be any different.

I think these are the 420 cam specs:
Intake Duration at 050 inch Lift 228
Exhaust Duration at 050 inch Lift 236
Duration at 050 inch Lift 228 int./236 exh.
Advertised Intake Duration 298
Advertised Exhaust Duration 306
Advertised Duration 298 int./306 exh.
Intake Valve Lift with Factory Rocker Arm Ratio 0.530 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio 0.551 in.
Valve Lift with Factory Rocker Arm Ratio 0.530 int./0.551 exh. lift
Lobe Separation (degrees) 114
Grind Number H-228/312-2S-14 T1.2