Flathead fuel

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May 20, 2022 | 08:57 AM

Eric1109

Thread Starter

Mountain Pass

Joined: Oct 2019

Posts: 196

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From: British Columbia

Flathead fuel

I have a 51 239 flathead. Was rebuilt nothing fancy. Don’t know of seats hardened. Set up with dual carbs. Was wondering what fuel to use. I know I need to avoid ethanol but what octane and as these engines ran with leaded fuel do I need to add a lead additive. Also in Canada seems only high octane is ethanol free

May 20, 2022 | 09:11 AM

Don Naslund

Laughing Gas

Joined: Sep 2014

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From: Whittier

Those engines were only 90 hp. You can use regular but if you plan to drive it hard, you should look for an additive to protect the valves.

May 20, 2022 | 09:13 AM

Eric1109

Thread Starter

Mountain Pass

Joined: Oct 2019

Posts: 196

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From: British Columbia

A lead additive.

May 20, 2022 | 10:32 AM

ReForder

Fleet Mechanic

Joined: Mar 2005

Posts: 1,462

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From: Dedham, MA

In some of the older cars I've had with non-hardened seats, I only added it if I planned on driving it "hard" (revving or hauling loads). I'd say you don't really need the lead additive, but it's a matter of preference and personal choice. I don't think you'll damage anything by adding it. I don't run it in my original 226.

I would consider when was it rebuilt. If it was recent, I would think (not assume, that's dangerous!!) they put it in hardened seats since lead fuel hasn't been available for some time.

May 20, 2022 | 10:33 AM

mtflat

Lead Driver

Joined: Oct 1999

Posts: 6,776

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From: Kalispell, MT

Regular pump gas is fine. 85 or 87 octane without lead additives.
Tore my merc flathead down after 10 years as a daily driver for new pistons. No evidence of damage to the valves after approx 100K miles across the US and into Canada (as far as Lethbridge)
Lead additives don't really do much.

Just my .02 - your mileage may vary

May 20, 2022 | 02:25 PM

abe

Fleet Owner

Joined: Dec 2000

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From: Central PA

I concur with both posts above. A "lead additive" really isn't lead. You do not need it unless as said above, racing or hauling loads daily.

I have not used lead additive in my 54 for 25 years and have not had a problem.

May 20, 2022 | 06:40 PM

HT32BSX115

Logistics Pro

Joined: Feb 2005

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From: Upper Left Coast

Quote:

Originally Posted by Eric1109

Those flat head engines have pretty low compression ratios. high octane gas is not really needed. 10% ethanol gas won't hurt a thing as long as you don't leave it in the tank for more than 6mo to a year or so.

You cannot buy lead additive. It's not sold anymore but if you must have leaded fuel, go to your local airport and tell them you want 100LL for your home built airplane engine. Expect to pay somewhere around $2.30-2.50/l for it though. Not sure if they'll sell it to you and I'm pretty sure if they catch you putting it in a car they might frown (or something worse)

I wouldn't waste money trying to "fix" a problem that is simply not there. I have run unleaded fuel in cars (that didn't have hard seats) since before it was widely available. I never had valve problems.

Just get the cheapest pump gas and drive it.