Gas Octane?

Raider2532 · Post by **Raider2532** » Mon Apr 16, 2012 8:27 am

Should I be using the highest octane of gas in my 1955 M38A1 or the cheap stuff(87 Octane)?

RICKG · Post by **RICKG** » Mon Apr 16, 2012 8:37 am

There are dozens of threads and opinions on this subject posted here.
Try the search function for a ton of info on the subject. Currently i'm
running regular unleaded pump gas with no problems (so far) but i
probably just jinxed myself..

Post by **wesk** » Mon Apr 16, 2012 9:37 am

The L134 was designed to run on gas as low as 63 octane. The military preferred the low rating so lousy fuel found in the field or accidentally diluted with diesel would not harm performance.

I mix 87 pump gas with 100 LL aviation gas in all my early engines. Pushes the octane up to about 90 even though I don't need it that high but more importantly it adds sufficient lead to protect the valves. I ran my M38A1 & CJ3B on 87 pump gas from 86 thru 98 without a lick of any problems caused by fuel type.

A word of caution to folks that add overdrives and push the old girls to 60 + MPH on long open highway runs you should add some lead or lead substitute.

53a1 · Post by **53a1** » Mon Apr 16, 2012 9:44 am

I took Wes' advise and I run 50/50 avgas & pump. So many benefits to doing this; shelf life, more lead, less ethonol. You don't need the extra octane points but it won't hurt. I've had the same tank of gas for a year now and it still runs great. My plugs look perfect so engine is happy.

Bretto · Post by **Bretto** » Mon Apr 16, 2012 10:13 am

Can the average joe just go down to the local strip and buy avgas? Or do you have to know someone? If that is the case, I think I know of someone who would help me out.

Post by **wesk** » Mon Apr 16, 2012 11:49 am

That varies with the Airport's FBO (Fixed Base Operator) and local state laws concerning road tax. Usually driving up to the FNO and handing the line service guy a 5 gallon container and asking for 100LL (LL=LowLead) for your homebuilt airplane is all you need to do.

Bretto · Post by **Bretto** » Mon Apr 16, 2012 11:57 am

I think I'll bring my aquantance along who has a plane there and have him help me out. I might end up looking like a fumbling idiot.

RCFlyguy · Post by **RCFlyguy** » Mon Apr 16, 2012 3:38 pm

I do the same thing for fuel as Wes. Except, I mix 4 gal of unleaded with 1 gal of 100LL. The reason being: I believe 100LL actually has 4 times the amount of lead as a regular leaded gasoline...plus it's a bit more expensive. When I took my engine apart, the valves and spark plugs have a greyish appearance to them (sign of good lead lubrication I think).

magnum · Post by **magnum** » Mon Apr 16, 2012 3:44 pm

If you use the lead substitute will it protect the valves the way the old leaded gas did?

53a1 · Post by **53a1** » Tue Apr 17, 2012 9:05 am

I don't know about your area but we have a small airport that looks like a ghost town and they have a self serve pump where you can pull your plane up to and use your credit card to fill up.

I also use the stuff with pre-mix in my '74 two stroke Yamaha and that engine actaully appreciates the octane.

Post by **wesk** » Tue Apr 17, 2012 10:03 am

Since the unleaded debut in 1972 I have never thrown any of my hard earned money at any of the commercial lead substitutes. They just aren't lead and not really a 100 % answer to the need for lead in these old engines. The only reliable person to answer your question is someone who has used the product religeously for a full overhaul life of a Willys 4 banger.

magnum · Post by **magnum** » Tue Apr 17, 2012 5:27 pm

Thanks Wes. I think the best way to go is with the Avaition fuel.