In 2000 I put a new 350HO in a 20' Imperial cuddy cabin. The engine has been flawless every season. It does call for 92 octane. I have used mostly 89 and some small amounts of 87 and really don't notice a big difference. With fuel cost at these levels, what would running 87 do to the engine? At this point I certainly don't want to compromise anything. I was just curious to hear from a good engine person out there.

Thanks
Tom

Boat motors run at maximum load coming on to plane and accelerating, the very small amount you save with 87 octane may well cost you a burnt or dropped valve or even a broken piston due to detonation.

I would stick with at least 89

Once I was filling up the scarab with premium and got a 4 hour dissertation on why I shouldn't use it. I'd go with what the mfgr says at the least.

a 350HO isn't a boat motor, that I know of. Sounds like a GM crate motor

You will destroy that motor if you continue to run it under a load with 87 octane,it was built to run on 92. I had one in a 1/2 ton truck a few years ago,if a gas station lied about their octane it would spark knock and rattle hard. It would rattle on 89 also,your problem is you'll never hear the detonation in a boat,it will just crack one of its hyperutectic pistons and come apart. I broke a piston at 22,000 miles on mine,switched them to forged,luckily the skirt that broke just made a constant ratlle and moved up and down with the piston instead of ending up wrapped around the crankshaft,Smitty