L78 & Today's Pump Gas?

[Bill Pritchard]

Will a stock 69 L78 with 11:1 compression run without problems on today's premium pump gas?

[mockingbird812]

Hey Bill. Sorry I missed yr email on this subject. You probably know this, but the bottom line is you can run whatever octane that allows you to avoid detonation. Here are some things to consider:
What is the true comp ratio for the engine. An L78 is supposed to be 11:1, but manufacturing standards indicate in reality that may not be true (less). Also, if the engine has been worked on, the published factory 11:1 may have changed (different pistons, heads shaved, etc. In practice, I cut my 93 octane (available here in OH) with a quarter tank of 110 VP racing fuel (you are lucky to have access to racing fuel on the reservations out in Phoenix area - it ain’t cheap though). In a pinch, I have gotten away with just 93 octane, but I’ve listened carefully for detonation.

Tom (Wilma’s Boy) has has/had a few.....

[WILMASBOYL78]

Trying to cut corners on fuel quality for a vintage L78 engine is a risky adventure. I understand some folks may not have access to race fuel, but finding it is worth the effort. These motors crave octane and run best with an aggressive timing curve...no place for low octane fuel. We have 112-115 Sunoco five minutes away...it ain't cheap, but it smells great, burns cool and make the L78 come alive. In a pinch I use 100 octane av gas...

Bottom line...find the best fuel...it's worth the time and money

wilma

[1971ls6]

Find a small airport and buy the 100 for $4.00 a gallon

[Xplantdad]

Bill...maybe try calling the RideNow Powersports location on the 202 and see if they still sell Sunoco racing fuel there? I know they used to sell it...as I would give it away as a prize when I put on car shows for Ridenow when I worked there



RideNow Powersports Chandler/Euro

2677 E Willis Road, Chandler, AZ 85286
Phone: 833-515-0876

[Lynn]

I am fortunate enough to have access to 100LL at a local municipal airport.

About 4 bucks a gallon. I don't even need to run it at 100%, but sometimes do.

About half and half with 92 works just fine. I don't have access to 93 at the pump around here.

IIRC I calculated the actual CR on my LT-1 spec engine at 11.25, and I simply could not run with aggressive timing on straight 92. Runs like a scalded dog on the AV gas and the timing bumped a bit. Aggressive curve, all in at 3k rpm, total mechanical advance of 38.
It was still pinging slightly even with timing back at 32 to 34. Tried Torco octane booster. I cured the pinging, but fouled plugs something awful. Still have about 3 gallons I would give away if someone wanted it.

[CanCOPO]

I also run 100 Low Lead (actually more lead than leaded gas back in the day) from my local Executive Airport. It's a decided difference in my 69Z 302 which has issues with 93 pump gas. I also have great luck adding tetraethyl lead.

[CanCOPO]

Available from Wild Bill's Corvette. Don't get it on your hands. I find it works as good as the avgas and much more convenient.

[big gear head]

My 427 is a true 11:1 engine and I'm running 91 alcohol free fuel in it with the timing turned down to 35 degrees. When I go to the track I use 110 with the timing at 39 degrees. No problems so far. I have open chamber aluminum heads which may make a difference.

[Chuck_Burg]

California 91 does NOT work in our L78! It is a 67 with closed chamber heads and NOS .030" over TRW pistons. 5 gallons of 110 leaded in each full tank make it run beautifully, 36 degrees total timing.