big diffrence in a boat vs a car.the boat motor runs under 100% load all the time,unlike a car.i say use the highest octane you can find.better to be safe than sorry.after all,gas is the cheapest thing about boating.

keep the timing where its at and listen for detonation,,install a knock sensor and gauge


like bob said you could radius the piston crown to relieve some compression, also get rid of the sharp points on the piston's, this will help with detonation. Take Bob's advise,he wont steer you wrong..if you use a thicker mls head gasket, i wouldn't go no more the .051 thick make sure you use head studs.. i run 10.2-1 in my little boat,355sbc on 93 fuel for 10 yrs,never no issues.. keep it cool and it should be fine..

What heads are you using? Are you sure you're 12:1? There are many ways to crutch your engine and make it run but none of them are right. Especially given the fact that you're building a second motor. The right thing to do and cheapest in the long run is to pull your motor apart and have the domes cut down. They are mos likely a solid dome and any competent machine shop will be able to mill the domes easily.
Also mrfixx the increased cylinder pressure from a SC is different then a high static comp ratio and running a thicker gasket to compensate on a NA motor is probably worse then running proper quench.. My .02

Also mrfixx the increased cylinder pressure from a SC is different then a high static comp ratio and running a thicker gasket to compensate on a NA motor is probably worse then running proper quench.. My 02..


that would depend on his deck height,, cheers

You are correct,the calculated compression ratio is that posted in my attachment. His actual mechanical compression ration is :

thanks for the input guys. will set the timing to 30, as well as use blended gas.

Cafe,

I would recommend against retarding the timing to prevent detonation as it will elevate your EGT figure significantly. Your actual compression ration is not 12:1. It ranges anywhere from 10.350:1 w/ 121 cc combustion chamber to 10.783:1 w/ 116 cc combustion chamber. These are easily managed numbers with 95 (RON+MON)/2 fuel.

Bob

Here are the 116 cc chamber calcs on your engine:

Get in touch with Bob and he can set you up with cams to get your dynamic compression where it needs to be to make your engines happy for a long time. After he's done mine though..

+1