I'm looking for opinions and information concerning fuel quality and older engines. I recently bought a boat that is 35 yrs old and has 350 engines that are still original and in great shape. The compression is still 135-140 on all cylinders and oil pressure is 65 lb at idle. The boat was pickled for many years and not used. The engine plate says NOT to use unleaded fuel and to use 91 octane or better grade. My question is - are there additives to allow unleaded fuel in this engine, with the higher compression (140 lb) is 93 octane unleaded OK if there is a lead substitute that can be used. My concern is detonation. Is there any info out there addressing this? I really don't want to tear the engines apart to replace the valves and seats and/or switch heads to get a lower compression. Any comments or advice appreciated.

joe, The compression is not high at 140 psi. Yes you can run lead substitute from autozone....the heads could be reworked with the hard sets....but save your $$$$.....if you don't run real fast .. leave it alone....If it knocks check timing .. then use the lead substitute...

jack carter

Jack - Sounds good to me. I don't run hard. Would you think a small retard in timing might be extra insurance say 3 to 5 deg?? Or would it cost too much in power loss.

Jack is right, use the lead additive, your engines had the harden valves but not the seats. retarding is not going to as you are going to be running 93 anyway, I have found a quart of auto trans fluid in each tank, will keep the heat down and you can run normaly.. Welcome to the board Smiling Jack.

MOST MARINAS PROVIDE 91 OCTAIN (MID GRADE) FUEL SO ALL YOU HAVE TO DO IS ADD THE LEAD SUBSTITUTE.

RELAX AND ENJOY.

Old houseboater made a typo, most marinas carry 89 octane fuel not 91. I have the only place on the Tenn that I know of with 93 octane.Where Old houseboater is docked at joe Wheeler carries 89, I was not thinking about the unavailability of 93 when I said you would be running it anyway. put a little octane boost and or a quart of trans fluid, you will be OK.

PIRATE

NOT A TYPO. MOST MARINAS INCLUDING JOE WHEELER CARRY 91 OCTANE. REASON FOR THIS IS THAT THIS COVERS BOATS REQUIRING REGULAR (89) AND MOST PERFORMANCE BOATS WHICH REQUIRE 91. SOME MARINAS ALSO CARRY DIESEL AND A VERY FEW CARRY 93.

Thanks for all the advice guys!!. I've never heard of transmission fluid in the fuel?? What's behind it?? I'm curious!! So could one of you explain?? How much oil to how much fuel. I've got twin 75 gal tanks. and pretty much up here on Old Hickory I find 89 octane available.