Airplane Fuel in 1970

[Al W.]

When having my engine rebuilt in my 1970 350/350 11:1 compression - the engine rebuilder states that the fuel from regular gas station pumps don't have the proper lubrications, etc. He suggested running airplane fuel but that is not reasonable. Are there any additives on the market that has the same additives that airplane fuel has that would do the same thing by adding to the gas station fuel? He also stated that if you don't use airplane fuel - there is a high probability that the rings in the engine will break again (this was the problem to begin with).

[Michael W.]

Re: Airplane Fuel in 1970

Very little of what your builder told you makes much sense or has truth to it. I hope he's a better builder than technician or engineer. Aircraft gasoline (avgas) has no magical additives that will overcome a poorly built or tuned engine, so it's possible that what happened before will happen again. Many Corvettes and similar muscle cars from the 60s and 70s have 11:1 compression and run just as well on today's pump gas as they did when were new. If they don't- it's not the fault of the gas despite people blaming it as seen in every corner of the internet.

The main difference between high octane pump gas and Avgas (typically LL100), of importance here is a relatively minor increase in the octane rating. This increased octane level could possibly forestall detonation under certain conditions- a severe case of detonation possibly causing cracked rings as you mentioned, but the engine would need to be somewhat out of tune with overly advanced ignition combined with both some hard driving and an owner that ignores the classic 'marble in a coffee car' sounds.

Short answer- if your engine is built and tuned properly, you won't need either Avgas or 'special additives'- very few of which actually work anyway. Concentrate your efforts on tuning and you'll be fine.

[Dan H.]

Re: Airplane Fuel in 1970

I've run over 20K with my 64 FI on 91 Octane pump unleaded, runs fine. Plugs have 11K on them, still look good. Agree with Michael. Back 'in the day' when we ran leaded fuel, we had to clean plugs once a Month and usually the rings gummed up after 50-60 thousand miles. Don't miss it at all.

[Joe R.]

Re: Airplane Fuel in 1970

Al,

You've gotten some good advice so far. Why do you think the compression ratio is 11:1? Is that based on Chevy advertising or actual measurements? Duke Williams covered your questions quite well in his presentation he gave at the 2012 national convention. I looked for his PowerPoint on this site, but didn't see it. He and John McRae also wrote an excellent article about managing compression ratio during engine rebuild. It's here, scroll down to page 5:

http://stlouisncrs.org/news_files/St_LouisNCRS_ChapterNewsletterSummer2012.pdf

Joe

[Jim T.]

Re: Airplane Fuel in 1970

My 68 327/350 original owner is still being driven with its 11:1 never apart engine. Have 96,500 miles on the L79 and runs very good. Two things I have experienced with todays pump gas is that the engine oil stays cleaner and spark plugs just last longer. It has been many years since I have changed the plugs. Even my 69 Triumph 650 motorcycle's spark plugs last much longer. I use premium in both with no problems.

[Gene M.]

Re: Airplane Fuel in 1970

Al,
I doubt you have an 11:1 motor, unless the builder specifically measured for and machined heads to get that. Just a head clean up of .006" and the use of a composition gasket will cut it way back. Custom pistons could get ya the real 11:1 but that is not a normal build. Everything would need to be assembled, measured and cc'd to verify they add up to 11:1. With a .038"-.042" composition gasket, and replacement pistons, not even close to 11:1.

Aviation fuel does smell sweet out the pipes I must admit ...........

[Duke W.]

Re: Airplane Fuel in 1970

The OP is new to NCRS and the TDB, so he doesn't have the benefit of the years of discussions we've had about all the myths and misinformation from "engine builders" and the Web.

Google my name along with NCRS and San Diego, and you'll find a site with a pdf of my San Diego PowerPoint slides:

http://www.metroli.org/pdf/2012%20Nationals%20tuningseminar.pdf

No doubt the OP has also been told all the engine oil myths, so he should read the engine oil article beginning on page 3
:

http://stlouisncrs.org/news_files/St_Louis_NCRS_Chapter_July_2011.pdf

Duke

[Steven B.]

Re: Airplane Fuel in 1970

When in HS I worked for a time at a county airport. I tried avgas in the '57 a few times expecting a great performance increase. Didn't get any earthshaking improvement.

[Michael W.]

Re: Airplane Fuel in 1970

When in HS I worked for a time at a county airport. I tried avgas in the '57 a few times expecting a great performance increase. Didn't get any earthshaking improvement.

Nor would it be at all possible for one to occur...............

[Rob A.]

Re: Airplane Fuel in 1970

What are the thoughts on cars that don't get driven much, does AV fuel have less issues with varnishing?

[John N.]

Re: Airplane Fuel in 1970

What are the thoughts on cars that don't get driven much, does AV fuel have less issues with varnishing?

Rob
I have used AV fuel in my 1969 350 350 HP since the 70's. The car is seldom driven and have had no fuel problems. Also use it in most other toys. I like the stability of the AV gas.
Regards

[Michael W.]

Re: Airplane Fuel in 1970

What are the thoughts on cars that don't get driven much, does AV fuel have less issues with varnishing?

I have used (primarily) E10 pump gas in my Corvette since the mid 90s's. The car is seldom driven and have had no fuel problems, including six month storage over the Canadian winters. Also use it in most other toys. No need for Avgas. Some owners in FL do report storage issues, no personal experience with that.

[Duke W.]

Re: Airplane Fuel in 1970

A lot of light airplanes are like vintage cars - they are both old and don't get used very much. SOP is to fill the fuel tanks after each flight, and then they sit - often outside.

Mogas has anti-oxident additives and most gasoline suppliers say the shelf life is one year. In practice, it's usually much longer. The lower the storage temperature, the less likely oxidation, so winter storage for six months is rarely an issue.

Avgas most certainly has similar anti-oxidation additives, but I don't know what the recommended shelf life is, but whatever it is, it's likely very conservative like most FAA requirements.

Until recently, the absolute only reason to use avgas instead of mogas in a vintage Corvette was to quell detonation, which is rare.

Recently the wide use of E10 has caused percolation problems, especially in warm climates due to ethaol's 170F boiling temperature. Avgas on average has a higher distillation temperature in the low to mid range, so avgas usually eliminates serious percolation that some E10 users are experiencing.

Duke

[Michael W.]

Re: Airplane Fuel in 1970

Avgas most certainly has similar anti-oxidation additives, but I don't know what the recommended shelf life is, but whatever it is, it's likely very conservative like most FAA requirements.

This might assist:

http://www.eaa.org/autofuel/autogas/articles/1What%20is%20the%20shelf%20life%20of%20avgas_.pdf

Storage conditions with Avgas is just as relevant as with Mogas.

[Steven B.]

Re: Airplane Fuel in 1970

While working at the airport we recommended aircraft hangered there be topped off. Storage and infrequent flight was no problem with fuel degradation.