The Stovebolt Site Forums The Shop Area Engine Shop Aviation Fuel in a rebuilt Stovebolt?

A local aviation mechanic has suggested that my rebuilt 235 c.i. engine out of a 1955 truck would really like a drink of aviation fuel. What do think about that idea?

Why?

I have heard of people using av-gas in HIPO motors, never heard of it in a 235. I have seen some people try to use it in a stock 80's f@rd and not only did they trow a rod real quick but it also melted their fuel lines and destroyed the fuel pump, not sure what kid of av-gas they were running.

If you plan on trying this out make sure your lines are rated for the fuel you use and let us know how it goes a video of that would be interesting.

Absolutely not. A 55 stick 235 motor has 7.5:1 compression ratio. Feed that motor regular gas. I have a 261 with giant size lumps on forged pistons and that motor runs on premium, not race gas, not AV gas, no supplements. So you will be fine feeding your nice little 235 motor regular!

Avgas burns so slowly that most of the energy will end up making the exhaust system red hot. No good can come of that. Back when a buddy was stealing it from Uncle Sam a few gallons at a time, we tried running 115/145 avgas in his hotrod Chevy. No joy there, either!
Jerry

Expensive type of gas!
It's ethanol free and has some lead in it.
Very high octane rating to avoid vapor lock at high altituedes... not needed for a normal stovebolt.

The high octane is to avoid preignition (knock), in high compression engines, NOT vapor lock.
But would be a waste of money to run in a low compression stovebolt engine, or any other automotive engine for that matter.

You'd think... however it seems most aircraft piston engines are <9:1 compression.

Fonz8261 Aviation fuel is great Iuse it in all 2 cycle engines . Starts and runs fine just costs about double !

....won't tell how I got it but back around '67 I kept a little around and on the weekends I'd dose the tank right good with a standard fill up and go racing. The old 348 with 3 duces would perk up a bit. The end of the exhaust pipes would turn white as a piece of cotton after a few runs on Saturday night. Good or bad we'd try anything we thought might help back in the day!!

100LL aviation fuel is the fuel in question. It was supposed to be replaced with lead free fuel by 2010, but it's still around today; see linked article. Some aircraft engines require 100 octane gas. Anyway, it's a waste of money in a stovebolt engine. If ethanol is the worry, some of the premium gas is ethanol free. Check gas buddy for a gas station near you that has ethanol free gas.

https://www.eaa.org/eaa/news-and-pu...-100ll-unleaded-replacement-complexities

But also frequently turbocharged, which makes detonation more likely.

When I had my LS6 454, my neighbour who had avgas offered me some, he said it was 108 octane. He had his own landing strip and hangar. I didn't know enough about it, told him I'd pass. Stuck to 94 from the pump. Certainly wouldn't run it in my stovebolt.

Agree on not needing Aviation gas it in a stock S'bolt engine. Mine does very well on the cheapest, lowest octane non-ethanol I can find. Not to take too much exception with others but back in the early 70's my local area didn't have any really high octane gas. The big city boys could find Sunoco 104 at a few select pumps. The Duster was running a 12 to 1 340 for a while back then and the local airport would reluctantly sell 5 gallon cans of gas (was it 100-130). I really don't recall the mix ratio with regular premium but you could run the timing where it needed to be at track day and still drive it on the street. Fortunately it didn't see many street miles.

Many think high octane gas makes more power and runs cleaner in their older street cars. In fact less power is usually the case if they don't have the compression needed to take advantage of the slower to ignite higher octane fuel. With our trucks I think 85 octane is fine. When just cruising down the road bobtailed, the wife's 6.4, 410 HP (at the tires) hemi truck does fine on 87 octane with it's knock sensors and computer controlled engine.... unless it's going to be working pulling a trailer then it needs/gets the highest octane premium around.

RonR

There are two kinds of aviation fuel. 80 octane is hard to find. 100 low lead most everywhere, neither have alcohol. 80 would no advantage other than no Alcohol. 100 low lead only needed on high compression engines. Melting fuel lines and pumps is due to something else!

Ed

This article talks about the differences between aviation fuel and fuel used in automobiles ("Avgas" vs." Mogas").

Avgas

You have to scroll down a ways because it also includes information about jet fuels as well.

According to this article, the basic chemistry of the two fuels (at least for 100LL) is nearly identical. The main difference is the addition of lead in avgas. While it is obviously helpful in controlling detonation (aka self ignition, in the article) it also lubricates valve seats and guides, increasing their longevity. I think its also important to remember that these engines are typically air cooled, so they are likely to run much high cylinder head temperatures than in an automobile. Apparently, avgas is also is required to meet specific quality standards unique to aviation fuel, and its vapor pressure is also lower than automotive fuels. This is to reduce the incidence of vapor lock at higher altitudes (as klhansen mentions).

Question: Do the any of the Chevy inline 6's like the 235 use hardened valve seats, or valve seat inserts? If not, that might be one reason the mechanic recommended avgas - in order to reduce valve seat wear. My GMC 270 has inserts from the factory, so I have never faced this problem. Do the Chevy guys who run unleaded fuel typically use additive(s) in order to the address this issue?

WRT to any catastrophic damage to the engine or fuel system (thrown rods, melted fuel lines, damaged pistons, etc.) I agree with EdPruss. These sound like urban legends to me - akin to "my neighbor/cousin/uncle/barber once ran premium fuel in a car designed for regular, and it ran so hot that it caught on fire and burned up". If these issues did occur, something other than 100LL avgas was the cause. Once again, the primary difference is how the formulation resists detonation. It does not burn hotter, nor does it contain significantly more BTUs per gallon than regular fuel. Its like insuring a $100K house for $200K. Just because you have the extra insurance, doesn't mean its any more likely to burn down.... (Well... unless my brother in law owns it, maybe...

One possible side effect, however, could be if you drive your truck in cold climates. The low vapor pressure may make it difficult to generate enough fuel vapor to start the engine when cold.

I would actually be much more concerned about the effects of using ethanol laced fuels than Avgas.

I know a guy who has been using Avgas in his '43 GMC for years, with no issues. He runs it because he lives near an airport, and there is a lack of stations with ethanol free fuel in his area.

Lastly, and I know this will be an important point to all of the responsible citizens on this site, there's no road tax on avgas, so (at least in my state) you are technically cheating the government out of revenue. Hope you will be able to sleep at night...

Best Regards.....

Road tax was the issue the local airport had when I first tried to buy their gas. Had to pull the Duster out on a trailer with slicks and open headers so they could see it really wasn't going to be on the road (much).

RonR

Lots of threads on various forums about avgas in automobile engines.

The 80 octane avgas (IF STREET LEGAL, WHICH IT ISN'T) would probably perform better in a 235 than 87 octane pump gas.

The 100 octane avgas is not going to perform well at all, unless the 235 is highly modified (maybe 12 to 1 compression, and timing BTDC of 40 degrees )

But the true believers will always believe, so:

Race gas IS LEGAL and some of it is 100 octane. Buy a barrel of racing gas and try it. HINT, don't fill the tank, because you are probably going to need to drain what you put in the tank, and sell it to your neighbor with the high performance Corvette.

And after the exercise is finished, if the 100 octane didn't destroy the engine, try the lowest octane you can buy at a name brand station.

And just for the record, my 450 HP 350 (measured 10.38:1 compression, not advertised) cruises just fine on 91 octane. If driven in anger, runs great on 93 octane. Runs well (but less well, especially until the engine is fully warmed) on race gas, and yes, I DID try it.

Remember, Dr. Werner Von Braun allegedly stated that 1 test is worth 1000 "expert" opinions. Try the test.

Jon.

When I was building "claimer" engines with "9:1" compression ratios (Actually about 10.5:1 after some sneaky angle milling) for the Nashville Fairgrounds oval track, the track management in its infinite wisdom (translation: "Greed") insisted that all the competitors buy their gas at the track- - - -"Pure Firebird Racing Gas" which was 106 Octane and cost nearly $4.00 a gallon. It was dyed a funky-looking blue color so a sample taken from a fuel cell could be readily identified. The engines ran really lousy on the stuff! By some dyno testing we discovered that premium-grade street gas with a little Diesel fuel added made my engines run a lot better that the track gas, so we only bought enough of the stuff at the track to leave a paper trail, and used machinists' blue Dykem to color our preferred fuel mixture. Like Smokey Yunick used to say, "It's only cheatin' if ya get caught!"
LOL!
Jerry

I've tried the 100LL avgas in a 235 and it ran like crap. The Farmall M loved it.

Around here now, we have good access to both 87 and 89 octane non-ethanol gas (serving the Marine community). My 261 runs equally well on both octanes.

John - surprised your Farmall liked it, unless it was a converted propane engine.

I love the comment under your name; if you have not seen the Ghia commercial with the Ghia coming out of the sunrise, Google it!

Jon.

Is it really a question of octane with a low compression engine or is it more trying to find a non-ethanol fuel. Like John said "marine " gas, it's available at the pump around here. I used it to run my 327 on for the initial start up, costs a little more but non-ethanol.

Jon -- have a link? I couldn't find it. Not really a Ghia fan, anyway -- just a pure Kafer/Type 1 guy

My original post has generated some interest--have enjoyed reading the comments.

Is one take-away from this conversation that our old reliable Stovebolt engines would like a regular dose of recreational "rec" gas?

Jerry, you tear me up with your comments.
Dycem, I may still have a can of that somewhere.
Can you even still buy it?

Don

Edit: https://www.zoro.com/dykem-layout-f...TJOtAq2MYILzH_APucSwVOzBUaQaAi1SEALw_wcB

John - Google Ghia barrier commercial

The short form is on the internet. The sunrise was part of the long form, which I remember when it came out. I loved VW commercials.

Jon.

Avgas has been around long before ethanol was added to highway fuel.
Marine gas has the same non-legal issue as non-highway avgas or farm diesel does, but it's harder to drive your car up to the fuel dock.

they trow a rod real quick
What do you think happened?

Don, I've got two colors of Dykem layout fluid, blue and red, and it's still available anywhere machinists' supplies are sold. Ditto for Prussian Blue paste for checking gear tooth contact patterns and scrape-fitting Babbit bearings.
Jerry

I have seen damage done first hand like I had said before, initially I had thought that the fuel was enough to damage the lines. Now after reading a bit of yall's responses I realize it was the heat coming off the block that melted the lines/damaged the pump/ threw the rod. I live out in the desert and it was summer (101-103 degrees outside when I was looking at their truck)). another factor was that they did not get their aviation fuel from the local airport (right next door) but from the 29 Palms marine base a town over, I DO NOT KNOW WHAT FUEL THEY WERE RUNNING just that it was aviation fuel. These people are from Landers (if you know the place you know what im talking about.) they crazy over there. Either way a low compression motor that doesn't breathe well will get very very hot using aviation fuel and may or may not cause damage (mostly heat related) probably depends on how much it's druven that way

I had the link to the story from our local news but it has been removed, it was a year or 2 ago so maybe the site dropped it or the marine base had it removed. oh yeah the fuel they were using they stole from the 29 Palms marine base, they have been charged and already payed the fines/sat in jail for a little bit.

I like that there Hotrod (Smokey Yunick) Its only cheatin if you get caught...How about (GRUMPY Jenkins and Dale Earnhardt) if you ain't cheatin you aint trying hard enough. Oh and by the way if you Bolters need any Dykem, look on line we by from a few different places....... I work for Lochkeed Martin......

Back in the 1960's one of the biggest cheaters in the drag race business was Dave Strickler ("Ol' Reliable"). One of his close competitors ran a 421 Pontiac with an acid-dipped body to lighten it up, and a front end made of aluminum so thin that leaning against a fender would dent it. That car was about 300 pounds lighter than an equivalent street model of the same vehicle!
Jerry

Interesting tread.. I build vintage British motorcycles for land speed racing. My one bike has held several world speed records . Getting 1.5 hp per cubic inch out of 1930's air cooled designs is a challange, the engines are stressed to the limits of durability and a small error in tuning can stick a piston...
The bikes have spent hours on the dyno be thrashed while tuning to get every thing it has..I'm no genius so I had to learn this from trials
and discussions with experienced engine builders.
Because of cylinder pressures ,high octane racing fuel is necessary...I use VP C12, a 110 octane leaded fuel. Once the 5 gallon can is opened so the fuel has a limited lifespan. After the racing I pour the few gallons of leftover race gas into my street bikes. The ratio maybe 50 to 80 percent depending on how much pump gas was in the tank...These bikes run fine on 91octane pump gas and run exactly the same on the high percentages of leaded race fuel...The pipes do get a light gray color just like back in the days of leaded pump gas.Nothing blows uo nothing gets red...
I do know both car and bike racers using aviation fuel and they do pretty good.It's not as good as race fuel in my opinion but it does suppress detonation.
Detonation needs time to occur, best way to avoid it is a faster combustion burn or fuel additives the suppress spontanous combustion of the perimter gases in the chamber. That's what the tetraethyl lead does...Saying hi octane fuel burns slower contradicts this...
There's a lot of info out there from fuel chemists and engine designers on this topic....

Is it possible that since the person in this story got this fuel from a military base, it might not even be gasoline but maybe jet fuel - such as JP-8 ?

As mentioned, anti knock additives suppress knock (detonation) by raising the autoignition temperature of gasoline - i.e. the air fuel mixture in the combustion chamber can withstand higher temperatures/pressures before it ignites on its own. The higher the level of suppression, the higher the octane rating.

Since fuels like diesel or JP-8 are not designed for (SI) spark ignition engines, the prevention of autoignition is not really a concern (the engines that use these fuels actually depend on autoignition, right?) Therefore, the octane rating of these fuels is extremely low. I found one site that put the octane rating of JP-8 at 15. It did not specify if this was RON or MON, but either way the point is moot, as the octane rating is essentially in the basement.

If a fuel like JP-8 was used in a conventional SI engine, I could see how the engine could experience severe levels of detonation. If run for any length of time this could lead to internal overheating and permanent damage.

WRT to 100LL, if someone can explain to me exactly how it will run perfectly fine in an engine with 10:1 CR and "destroy" an engine with 7:1 CR, I would really like to understand the specifics of how such a thing can happen.

As also mentioned previously in this thread, many have run 100LL in low compression engines without experiencing any damage. Due to its lower vapor pressure, I can see how its use could lead to cold weather starting or drivability issues, but I have a hard time believing that it will cause catastrophic engine damage.

Best Regards....

I was an aircraft mechanic who specialised in jet engines, piston engines, recip engines, turbo props etc.

Av gas wont hurt your engine, it is however illegal to use in some locations, go figure, put it in your car and drive and the pollution is illegal, put it in a plane and pump it out in copious volumes and its perfectly fine.

We had 44 gallon barrels of the stuff and ran our cars in the 80s all the time on it, when you have to do fuel cell work in a plane, it has to be defueled, the fuel that comes out is not allowed to be re used in a plane, so it gets disposed off, most aviation fuels wont work in a car but the av gas does as its designed for piston engine planes

Steve