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Expert
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Location: Valley Forge, Pa. | My friend has a 68 Chevelle 396/375HP[Holley] and a 70 El Camino 396/350HP[Rochester]. My friend only runs high octane airplane fuel in his cars at $7+ a gallon.
I asked him why? He said that the garage told him to ONLY run airplane gas. Says that todays gas will ruin his carburetors.
I remember hearing that when this current gas became common it would destroy the original carb gaskets.
I thought todays rebuild kits had alcohol resistant gaskets. I've run non-alcohol gas for 20 years in my Suburban and have had no issues. I've had carb problems but not related to the gas.
The guy at the garage says he rebuilds 80 carbs a year because of modern fuels.
Is that right, should I be paying $7-8 gallon for non-alcohol fuels? I ran it in my 67 GTO also. |
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Exner Expert 10K+
Posts: 10063
Location: So. Cal | Which is more expensive, to rebuild your carb every 5 years or to pay $3 extra per gallon every time you want to drive it. I think the carb rebuild will be a bargain in comparison. But nevertheless, I haven't really had a problem with it either. The fuel pump is probably the most likely part to suffer from it. |
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Expert
Posts: 2007
Location: Branson, MO | Amen Powerflite! No argument here. |
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Location: Under the X in Texas | "AvGas" aviation gasoline is also called 100LL (100 octane low lead) That 100 octane rating is in the air at some altitude level because octane measurement is relative to altitude above sea level. That is why in mountain states like Colorado they sell lower octane rated fuels. AvGas is approximately actual 90 octane for the first couple thousand feet above sea level. I live at 2000' above sea level.
I purchase "90 octane leaded gas" from a local fuels distributor who happens to supply our small local airport. You can figure out what it is. YES, road tax IS included in the price. And that price about 10 days ago when I last pumped into my '55 Imperial's 331" Hemi was $4.59. Pump 87 octane "regular" is currently $2.99 in my city.
AvGas is the sweetest smoothest running fuel I ever driven. I'm not having any sort of problems with carburetors or fuel pumps or gaskets or diaphrams or whatever. Past research indicated the actual lead content of AvGas is quite low, much lower than our historical leaded gasolines at popular service stations. |
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Expert
Posts: 3082
Location: N.W. Fla. | Unless you got really high C/R E-0 should be good, here it's available up to 93. I once had a Mustang with a 351C-4V that was 10.7 & the book called for 98 octane, but most engines don't need really high octane. If it's a hemi the rule of thumb is it'll be good as a wedge engine with one point lower C/R as far as octane is concerned. |
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Expert
Posts: 1756
Location: Alaska | 100LL is only "low lead"in comparison to the old 130 octane avgas that has not been available for a long time. It has a lot of lead in it. One of the issues with this gas is you will be changing spark plugs more often because of the lead deposits. The main problem with todays auto gas is the alcohol that is added to it. This is what is harmful to the fuel system in older cars. |
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Expert
Posts: 1357
Location: Valley Forge, Pa. | Powerflite - 2024-08-03 11:20 AM
Which is more expensive, to rebuild your carb every 5 years or to pay $3 extra per gallon every time you want to drive it. I think the carb rebuild will be a bargain in comparison. But nevertheless, I haven't really had a problem with it either. The fuel pump is probably the most likely part to suffer from it.
Not only the cost but it can dictate where you can go. It's like an electric car driving across country. You need to look ahead to line up charging stations. A 21 gal. tank at $7+ per gal. would cost around $150 per tank. Probably save around $50 per tank full running regular high test. That might be a couple $1000 saved between rebuilds. He doesn't race his cars and occasionally he will jump on it to get the rush but 375HP with 93 octane should put in back in his seat well enough..
What does the alcohol gas do to a vintage carburetor? Are modern gasket sets made to tolerate alcohol? When alcohol fuels were becoming standard, I heard that it ate the old paper gaskets? Isn't that the issue with current gas?
It's hard to believe that companies like Holley[ect.] that make carburetors are still using gaskets the can't hold up to current fuels. Same with new carburetor kits? |
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Expert
Posts: 1357
Location: Valley Forge, Pa. | Powerflite - 2024-08-03 11:20 AM
Which is more expensive, to rebuild your carb every 5 years or to pay $3 extra per gallon every time you want to drive it. I think the carb rebuild will be a bargain in comparison. But nevertheless, I haven't really had a problem with it either. The fuel pump is probably the most likely part to suffer from it.
Not only the cost but it can dictate where you can go. It's like an electric car driving across country. You need to look ahead to line up charging stations. A 21 gal. tank at $7+ per gal. would cost around $150 per tank. Probably save around $50 per tank full running regular high test. That might be a couple $1000 saved between rebuilds. He doesn't race his cars and occasionally he will jump on it to get the rush but 375HP with 93 octane should put in back in his seat well enough..
What does the alcohol gas do to a vintage carburetor? Are modern gasket sets made to tolerate alcohol? When alcohol fuels were becoming standard, I heard that it ate the old paper gaskets? Isn't that the issue with current gas?
It's hard to believe that companies like Holley[ect.] that make carburetors are still using gaskets the can't hold up to current fuels. Same with new carburetor kits? |
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Expert
Posts: 1290
| Lads --
Since the old Rochester fuel injection system on my '65 Corvette requires leaded fuel for its lubrication and that 327 CID mill has 11:1 compression, I put 5 gallons of 110 octane leaded racing gas in each tankful (20 gallon capacity) with the rest of the tank being the highest octane pump gas I can get. Since I got into that habit (of 5 gal. 110 octane) with the Vette, I also do the same with my '57 300C, '60 SonoRamic Fury, and '65 Sport Fury 426 Street Wedge. Of course, the C (with a 23 gallon tank) came off the line with hardened valve seats and 9:1 compression, so it doesn't really need either the higher octane or leaded fuel. However, while I did pull the heads on my '60 Fury (20 gal) and had a valve job done, that ol' ram-inducted engine does have a 10:1 ratio and runs much better with the mix. I haven't done any work yet on the 426 in the '65 SF (25 gal), but I play it safe especially since its mill has a 10.3:1 ratio.
In view of the fact that I've never taken any of them on extremely long trips (1000+ miles), this practice has been fairly successful, if costly (last week, 110 octane was $8.999/gal). So far, no carb or plug problems (knock on wood) and, as should be expected, the cars have outstanding performance.
Inicidentally, I've done this with the Vette since 1985, the Fury since 2000, the C since 2006, and the SF since 2016.
Joe Godec |
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Exner Expert 10K+
Posts: 10063
Location: So. Cal | A 10.3:1 ratio on an iron-headed hemi is equivalent to around 9.3:1 on a wedge. Aluminum heads would reduce the need for octane even further, typically by another point. So using high-octane fuel on a 9.25:1 392 is really overkill. I have to be careful with the timing setting on my 10:1 DeSoto wedge engine & 10:1 340 engine if I want to run mid-grade unleaded, but I can make it mostly work. But my 10.5:1 392 that I ran had no issues at all on regular unleaded. Granted, it might have been only 10:1 due to thicker head gaskets because I'm not sure when that compression spec was created for the pistons. But hemi engines definitely have less issues with pre-ignition. That's why it's such a crime for people to use stock pistons in those engines. Take away another 1/2 point due to modern head gaskets, and you are really far away from running the engine at it's true potential. And the higher compression pistons that it can easily use allows you to get away with a wilder camshaft too, all without causing problems driving it as a street car. |
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Extreme Veteran
Posts: 311
Location: Newcastle Australia | I'm going to make an assumption here, that fuel production in the US is the same as in Australia.
If that is the case, then there is no difference between auto fuel and aircraft fuel.
Different additives are used to achieve the different octane levels. But the detergents etc are exactly the same.
Naturally, ethanol based fuels are different and shouldn't be used unless the car has been modified to run with ethanol. |
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Expert
Posts: 3445
Location: Chestertown, NY ( near Lake George) | I will say here that advertised compression in these engines is based on minimum blueprint specs. My 64 Maxwedge race car, when built for competition had cylinder head ccs that were 4 ccs over the factory specs, deck height was .008 over spec., so it worked out to about 11.7:1, not the stated 12.5. All corrected during the build of course. Found similar issues on my friends 70 Challenger Hemi car.
Edited by Shep 2024-12-26 3:36 PM
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Expert
Posts: 3822
Location: NorCal | lozrox58 - 2024-12-26 12:26 AM
I'm going to make an assumption here, that fuel production in the US is the same as in Australia.
If that is the case, then there is no difference between auto fuel and aircraft fuel.
Different additives are used to achieve the different octane levels. But the detergents etc are exactly the same.
Naturally, ethanol based fuels are different and shouldn't be used unless the car has been modified to run with ethanol.
In the U.S. ethanol is widely used as an octane booster, typically 10%. Ethanol is corrosive to some metals and rubber.
Avgas gets its octane boost from TEL. |
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Elite Veteran
Posts: 657
Location: Lubbock, TX | Also ethanol based fuels are only stable for roughly 6 months of storage, after that the water content seperates from the alcohol and it'll lose it's volatility. So if you're storing cars or any internal combustion engine for a period of time the ethanol fuel will go bad and need replacing. Avgas 100LL is stable for like 2-3yrs I believe. |
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? on airplane fuel
