Hi, Northwester,
After reading your post and the various replies to it, I think there is one option that you might have missed. That option is water injection. If you're attempting to control detonation, there is no better solution. In the 1970's, I had a Chevelle El Camino with a big block Chevy V-8 in it and somewhere in the neighborhood of 11 or 11.5 to 1 compression. By 1976 or so, there was no gasoline available at any gas station that would not detonate fiercely as soon as I started the motor, and I wound up parking the El Camino for most of a year because I was afraid of ruining the motor and didn't have the money at that point to do a complete rebuild with lower compression pistons. Around 1979 I heard about someone marketing an aftermarket water injection setup that was supposed to control detonation. It was made by one of the main aftermarket speed equipment companies (although now I don't remember which one)and didn't cost a fortune, so I bought one and installed it on the El Camino. It worked to perfection. I still had to run premium fuel, but the detonation was completely gone.
I still don't remember the name of the company who made my water injection, but when I put "water injection" in the search field on eBay, I usually get a few hits on NOS Holley or Edelbrock water injection units produced in the late 70's for the exact problem that I had. Recently I have done a bit more research and found that although Holley and Edelbrock no longer make water injection systems, there are companies whose entire product line is water injection kits and parts. Coolingmist is one of them, and they make kits for both turbocharged and normally aspirated engines. The normally aspirated setup sells for about $200 US, so they're definitely affordable, and judging from their literature, they're also better quality than the old Holley and Edelbrock units.
You can run distilled water, and I have heard from people who should know about these things, that you can also use windshield washer fluid in them with no problems. Besides controlling detonation in an engine, they also keep it cleaner internally due to a sort of natural steam cleaning of the cylinder head and piston crown when the engine is running, so you don't get the normal carbon buildup. You can do a search for Coolingmist, but I think their website is
www.coolingmist.com if you want to try looking at it. If that address isn't right, just do a google on Coolingmist and you'll have it.
As far as the rest of you engine project goes, it sounds like you've done your homework well. Except for maybe the roller cam idea. A flat tappet cam will work just fine for what you want the engine to do. Roller cams are generally meant for high rpm engines, which you apparently don't need or want in your boat. I think probably an RV type of cam with a power band from 2000-5000 rpm would be just the thing for your boat motor.
Good luck with the project. It sounds like fun.
