What octane fuel for the motors?
 

454 BBC with twin intercooled turbos, Draw thru carb 7:1 compression running 10lbs of boost. The boat has 3 tanks. Both motors can draw thru the belly tank and each one can draw off it's own saddle tank. I was planning on using the center tank for cruising and the saddle tanks for WOT conditions. What octane should I use in the belly tank and the saddle tanks?

Re: What octane fuel for the motors?
 

I would think 89 would be good. to play it safe. On a boat I used to have there was a dial wired into the MSD7 ignition that would retard the timeing from 1-3 degrees for each pound of boost.
I ran 89, no intercoolers, but limited my boost to 7-8, on 7.5:1 compression.

Re: What octane fuel for the motors?
 

If you were running a msd boost retard the 89 should be safe but if your running fixed timing i would run 92 or 93 just to be safe in the saddle tanks,especially since you are cruising on cheaper gas,it would still be economical. I love the idea of a different gas tank that you draw fuel from under boost,i wish i could do that on my boat. as far as the center tank,your essential running a 7-1 motor when not under boost so i don't see why you couldn't run 87 octane,Smitty