QUESTION ON AVIATION GAS COMPATIBILITY for Duke and all

[Clem Z.]

Re: QUESTION ON AVIATION GAS COMPATIBILITY for Duke and all

100 LL is about 106 octane the way they rate auto fuel so mixing it 50/50 with 93 octane you will have close to 100 octane. when my son was racing dirt bike hare scrambles on 2 stroke bikes and that is the mixture we used 50/50 high test and 100 LL

[Michael W.]

Re: QUESTION ON AVIATION GAS COMPATIBILITY for Duke and all

Will 100LL gas work in a pre-70's Corvette engine? Why not. 100 leaded was available back then.
Doug

Yes, it will work just fine- but there's high probability that the appropriate octane level of pump gas will work just as well, is much much cheaper, available everywhere and is 'street legal'.

What problems are you presently experiencing?

[Joe L.]

Re: QUESTION ON AVIATION GAS COMPATIBILITY for Duke and all

Yes, it will work just fine- but there's high probability that the appropriate octane level of pump gas will work just as well, is much much cheaper, available everywhere and is 'street legal'.

What problems are you presently experiencing?

Mike and Doug-------


Absolutely. And as I've repeated many times previously, lead is good for octane and it's good for exhaust valve seat protection but, it's bad for everything else in the engine and there are a lot of other important things in an engine. If you don't need the octane and you don't need exhaust valve seat protection (and virtually no Corvette engines really need that protection), then you don't need 100LL.

I think that a lot of the impetus for folks to use 100LL has a lot to do with the "cache" associated with it. In other words, telling folks or just thinking that one's Corvette engine is so special it needs "aviation fuel". The truth in the vast majority of cases is that Corvette engines don't need it and, as a matter of fact, would be better off without it.

[Michael J.]

Re: QUESTION ON AVIATION GAS COMPATIBILITY for Duke and all

I have been tempted to try the gas available at a nearby Conoco station. There are two small pumps along side the dozen or so regular pumps that are marked "Racing Fuel 105 Octane". I asked the attendant about it and she didn't know anything except that the local racers with old cars use it quite often. Anybody know what this stuff could be? Would it be safe to try in my stock L71?

[James G.]

Re: QUESTION ON AVIATION GAS COMPATIBILITY for Duke and all

Lead and Ethanol, two villains, two different issues.

The lead put in clogs up the valve seats in a huge way. I had engine parts come back that you could not believe, deposits built up that essentially close up the combustion chamber. Don't have pics from so long ago but the fuel manufactures are supposed to put another highly toxic compound in to "get the lead out" of the combustion chamber. I'd have to break out that Org Chem E book to think back that far.

By the mid to late 70's most GM engines I am aware of had heat induction hardened valve seats and lead was no longer needed.

So - eliminating lead from av gas - welcomed.

Alcohol - meant for anything but the gas tank. When that was first introduced, most likey it was a combination of poor underground storage as well as incompatibility of the fuel system components. We had lines coming back, the tern coat all clogged up carbs corroded beyond all belief and recognition and more. Alcohol is a powerfull solvent, hygroscopic, that means it sucks up water from the air, or any other source. In those days, on the cusp of the EPA, it was very common to have water runoff get into the underground tanks, worse salt water run off in the winter. So that mix of alcohol, a little water and dissoved salt in my opinion was why we have such a "time" with the turn coat coming off and plugging new car fuel systems to the max. If you think about it, it was not until the late 80's and into the 90's that service station testing was in full force and EPA clean up required for leaky tanks. That helped clean up the fuel supply considerably.

However, on a 44 year old car that never saw alcohol before in any concentration, by the time I got to the second tank the fuel sender was shot and we'd find later the power valve in the carburetor too. It was at that point I bucked the gov't corn lobby imposition and move to the pure stuff.

Ron, I was in the retail Gasoline business with Shell, Union 76 and Chevron from 1965-94. And California Smog Tech the same time. Your industry analysis is so correct. Zora Duntov told me in the 80's that "fuel injection" was designed for the SMOG problem in California and other cities, with the benefit of more power. He predictied "all" cars would be fuel injected some day. Well here we are, and the benefits of EFI and modern electronic ignition systems allow the engine to run on almost anything, including corn. But the Goverment has to let you and the "Duke's" of the world keep the engineering alive and well, so we can continue to get to the store to buy more ice cream.

I went to NASCAR in Fontana last Sunday. The "roar" on the 1st lap was great.......but the lack of the "smell" of no 110 leaded was missing. We have lived in the great "Glory Days of America"

[Duke W.]

Re: QUESTION ON AVIATION GAS COMPATIBILITY for Duke and all

100 LL is about 106 octane the way they rate auto fuel so mixing it 50/50 with 93 octane you will have close to 100 octane. when my son was racing dirt bike hare scrambles on 2 stroke bikes and that is the mixture we used 50/50 high test and 100 LL

It's closer to 104-105 PON, 108-110 RON; 100LL uses the Aviation Method to determine octane number, which yields about the same value as the Motor Method, which is usually 8-10 points less than the Research Method, which is the way mogas was measured back in the sixties.

Mogas is now the arithmetic average of MON and RON, so a 50/50 blend of 100LL avgas and 93 PON mogas, would be equal to about 99 PON, or 104 RON, which would be good for a L-88.

Any other production engine should not need more than about a 25 percent blend of 100LL if the CR is anywhere near typical for a production engine including engines rated at 11.25:1, but since most engines as built by Flint have half a point lower CR than advertised, most vintage engines don't need more than modern pump premium, but some, especially SHP big blocks, might have to run with slightly reduced initial spark advance to keep out of detonation.

Duke

[Duke W.]

Re: QUESTION ON AVIATION GAS COMPATIBILITY for Duke and all

I have one additonal prespective on this question. 100 low lead gas has remained available for aircraft use because there are a LOT of reciprocating aircraft engines out there that were built before the 1970s. My Beech Bonanza was built in 1961. It has always been my understanding that those old engines need lead for valve lubrication and that they were designed to run on 100 octane gas. In any event every aircraft type was put through some pretty rigorous testing to obtain FAA certification. If something changes on the plane, even something like a change of fuel type, the certification goes out the window and the process starts again. I can not legally run anything but 100L in the Bonanza. If 100LL goes away there will be big headaches for a lot of general aviation owners, probably in the form of their aircraft being grounded. Pilot-Owner groups will fight the FAA on this.

Will 100LL gas work in a pre-70's Corvette engine? Why not. 100 leaded was available back then.
Doug

Aircraft engines usually have Stellite valve seats and Inconel valves, so they really don't need TEL, but when you're cruising at 8000 feet, the throttle is wide open and you lean it out as much as possible, the EGT is probably around 1300-1350 degrees F. Auto engines don't see sustained exhaust flow/EGTs that high.

The O-520 and O-540 engines used in the Bonanza have a bore over 5" - almost as much as an Allison or Merlin. Detonation tendency increases with bore size, and 6" is the practical limit, though I think there was at least one large aircraft engine of yore that was 6.25".

Despite a CR of only about 8:1, the Bonanza needs high octane due to the large bore. Also, aircraft engines may have to run at sustained load much longer than auto engines, so they are very conservatively designed and certified. If you get into detonation climbing out on a hot day at gross weight and the engine self destructs, the result may be a fatal accident.

There's absolutely no reason why 100LL won't work in any auto engine. The only downside is possible hard starting in cold weather due to avgas' low vapor pressure to prevent vapor lock at high altitude.

By the same token, no production engine needs 100 percent LL, but a very few might need a small blend of avgas or other higher octane gasoline to avoid detonation.

Duke

[Duke W.]

Re: QUESTION ON AVIATION GAS COMPATIBILITY for Duke and all

I have been tempted to try the gas available at a nearby Conoco station. There are two small pumps along side the dozen or so regular pumps that are marked "Racing Fuel 105 Octane". I asked the attendant about it and she didn't know anything except that the local racers with old cars use it quite often. Anybody know what this stuff could be? Would it be safe to try in my stock L71?

The first question is what method was used to come up with 105. The next question is do you need it?

If you find out the brand and type, you can probably find a spec sheet on the Web.

Duke

[Duke W.]

Re: QUESTION ON AVIATION GAS COMPATIBILITY for Duke and all

Don't have pics from so long ago but the fuel manufactures are supposed to put another highly toxic compound in to "get the lead out" of the combustion chamber. I'd have to break out that Org Chem E book to think back that far.

Those are know as "lead scavengers" - organic compounds with bromine molecules. Lead bromide is a gas, so it gets ejected out the exhaust. Without the scavengers, lead oxide, a white colored solid, can form excess deposits.

Most leaded fuels are blended with sufficient scavengers to keep lead oxide deposits to a minimum, but back in the days of leaded mogas, engines that were rarely run hard could see excess lead oxide deposit buildup unless they got an occasional Italian tuneup.

Duke

[Michael J.]

Re: QUESTION ON AVIATION GAS COMPATIBILITY for Duke and all

The first question is what method was used to come up with 105. The next question is do you need it?

If you find out the brand and type, you can probably find a spec sheet on the Web.

Duke

Thanks Duke, I will do a little more investigation. Since I worked for Conoco for 30 years I will ask the downstrem folks where it comes from and how it is made. It has a sign warning not to be used by cars with catalytic converters, contains tetra-ethyl lead. I guess I probably don't need it as my L71 seems to run just fine on regular 10% ethanol 93 octane pump gas, no pinging. Just thought it might be interesting to try a tank or half tank and see if I feel any difference.

[Domenic T.]

Re: QUESTION ON AVIATION GAS COMPATIBILITY for Duke and all

Mike and Doug-------


Absolutely. And as I've repeated many times previously, lead is good for octane and it's good for exhaust valve seat protection but, it's bad for everything else in the engine and there are a lot of other important things in an engine. If you don't need the octane and you don't need exhaust valve seat protection (and virtually no Corvette engines really need that protection), then you don't need 100LL.

I think that a lot of the impetus for folks to use 100LL has a lot to do with the "cache" associated with it. In other words, telling folks or just thinking that one's Corvette engine is so special it needs "aviation fuel". The truth in the vast majority of cases is that Corvette engines don't need it and, as a matter of fact, would be better off without it.

Joe,
With all respect to your knowledge I have to blow my horn again.
My chevelle needs 100LL also.
If I don't use it 50/50 it runs like a truck engine. Once you use it you won't want to drive your car without it.
The most important thing to me is that I DO NOT have to de- tune the engine to run on a fuel octane that it was not originally designed to run on.


Some one also said that they run good on pump gas, NOT IN CALIFORNIA.
They would have to define run good to me. It's more like driveable. I want the power that the engine was designed to have in my car.
It seems to me that if one can't use 100LL they defend what they are STUCK with.
The only difference I have seen since they made pump gas cheaper by reducing the octane is that of Knight and day.
The corvettes with dish pistons are the only ones that can get along with pump gas. If you remember back then the large chevy trucks had dish pistons, then in 1971 they put them in cars.
The engine that runs good on pump gas was desigened to run on it.

DOM

[Michael W.]

Re: QUESTION ON AVIATION GAS COMPATIBILITY for Duke and all

Domenic,

Today's 93 octane is roughly equivalent to 98 octane in the 'good old days' due to the change in rating method in the mid 70s. Gas stations in North America now advertize octane rating as an AKI (anti knock index) rather than the former method of displaying only the RON. Most other countries still display RON. This confusion causes many to believe that our gasoline is of a lower octane number.

What does 'run like a truck engine' mean specifically?

[Domenic T.]

Re: QUESTION ON AVIATION GAS COMPATIBILITY for Duke and all

Michael,
You would have to drive one to know, hard to explain. No snap to the throttle etc.

I CA we only have 91 octane and it pings badly. With my timing where it's supposed to be, my engine pings. I have used water injection with pump gas and it gets rid of the ping but the performance is not what it is with the 50/50 blend.

DOM

[Joe L.]

Re: QUESTION ON AVIATION GAS COMPATIBILITY for Duke and all

Joe,
With all respect to your knowledge I have to blow my horn again.
My chevelle needs 100LL also.
If I don't use it 50/50 it runs like a truck engine. Once you use it you won't want to drive your car without it.
The most important thing to me is that I DO NOT have to de- tune the engine to run on a fuel octane that it was not originally designed to run on.


Some one also said that they run good on pump gas, NOT IN CALIFORNIA.
They would have to define run good to me. It's more like driveable. I want the power that the engine was designed to have in my car.
It seems to me that if one can't use 100LL they defend what they are STUCK with.
The only difference I have seen since they made pump gas cheaper by reducing the octane is that of Knight and day.
The corvettes with dish pistons are the only ones that can get along with pump gas. If you remember back then the large chevy trucks had dish pistons, then in 1971 they put them in cars.
The engine that runs good on pump gas was desigened to run on it.

DOM

DOM------

I could easily get 100LL if I wanted to use it. However, I don't for the reasons previously stated. If I had an engine that needed it, I'd find some other way to make it run without it, including engine modifications. I like to be able to pull into a gas station ANYWHERE and fill up my tank. I don't want to be "tethered" to a cruising range limited by my ability to get back to my source of 100LL. I don't like filling my tank from a jerican or the like, either.

In fact, I built the "ZL-1" with 9.0:1 compression (just like 1971 LS-6) just so I'd have no problems with fuel. 2 extra points of compression (or more) just wasn't worth the fuel hassle I might create for myself, especially when I'll have more power than I could possibly use on the street, anyway. If I'm lucky, I might even be able to get by with 87 or 89 octane fuel. That gives me even more fuel options when I pull into a gas station. And, you can be sure that if I find I can run it on 87 or 89 octane, I won't be filling it up with 91 octane just to impress someone filling up next to me.

By the way, I once built a 350 with 10.25:1 compression (real; not advertised) and could run it on 87 octane fuel with absolutely no pinging problems, whatsoever.

[Domenic T.]

Re: QUESTION ON AVIATION GAS COMPATIBILITY for Duke and all

Joe,
I agree about the gas station and the convienience, but when I decided to restore my car I didn't want to modify the power plant. I want it to be as real inside as outside.
I can drive cross country with timing changed and water injection. But the urge to blow away a Porche has to cancelled.
My son modified a 68 camero with a 350 to run on pump gas and it does as good as the old engines did.
But if your stuck with stock in these cars you do what you have to if you want original performance.
It's a great pleasure to blow away a late model car on the road, I can't resist the urge to show them what the cars were like in my day.

DOM