Aviation Gas (Avgas)

[Wayne Stambaugh]

I searched the forum for Avgas and only came up with a couple of posts. My Caterham has a 1.6 BDR and everything I have read indicates it should only be run on leaded gasoline. Today it’s difficult enough to find non-ethanol gasoline much less leaded gasoline. That ship has sailed and we will never see leaded auto fuel again. Fortunately I’m a pilot and have access to 100 LL avgas. It’s not cheap but it is definitely leaded and although the octane rating is not calculated the same as auto gas it’s still higher octane than pump gas we ever was. There are obviously race gasolines on the market but their price is outragous. Today at my airport 100 LL avgas costs $6.25 a gallon. Since the Caterham won’t be an everyday vehicle I can easily afford to burn it. I was wondering if anyone else is burning 100 LL in their cars and what kind of experience they have had with it. (obviously cars with catalytic converts can’t run leaded fuel anyway)

[MV8]

100ll is still a lot more lead per gallon than leaded auto gas had. Just not worth the trouble you could get into. I suggest additives instead or have hardened valve seats installed if or when the valves sink/no longer seal to make normal compression. The hardened seats will replace the worn area.

Edited October 28, 2023 by MV8

[jbcollier]

Most aluminum heads already have hardened exhaust seats.  The problem was with cast iron seats which I would doubt your engine has.  Do not take my word for it though, talk to a race-engine builder who is familiar with BDAs.

 

If it is a concern, I would pull the head and have the seats changed.  Lead is really, really nasty stuff.

[Wayne Stambaugh]

1 hour ago, MV8 said:

100ll is still a lot more lead per gallon than leaded auto gas had. Just not worth the trouble you could get into. I suggest additives instead or have hardened valve seats installed if or when the valves sink/no longer seal to make normal compression. The hardened seats will replace the worn area.

I just Googled lead additives/replacements and didn’t have any idea how many are on the market today. That’s an easy solution to get started with. In time if for some reason the cylinder head ends up needing to be removed I’ll address the valve seats then.

[jbcollier]

There are lots out there.  Some are so much snake oil.  Look for reviews from reputable organizations.  I know there are at least a couple out there that have been long in use with great success.

 

People complain about today’s fuels but they are much, much cleaner than fuels were in the 60s and 70s.  We used to do lots of decarbonizing and valve grinds back in the day.  Now, virtually unheard of.

[Wayne Stambaugh]

22 minutes ago, jbcollier said:

There are lots out there.  Some are so much snake oil.  Look for reviews from reputable organizations.  I know there are at least a couple out there that have been long in use with great success.

 

People complain about today’s fuels but they are much, much cleaner than fuels were in the 60s and 70s.  We used to do lots of decarbonizing and valve grinds back in the day.  Now, virtually unheard of.

Yes, fuels are cleaner. They are currently working on unleaded aviation fuel as well. I don’t think its going to be long before that’s all we can get.

[MoBoost]

I’ve stayed away from additives because of the concern that they can cause deposits in the combustion chamber. I use good quality fuel (Mobil 93 octane). The valves and seats are modern materials and my valve clearances remain within spec. I’d also state that I haven’t been thrashing the car on track, so that would also be a factor. 

[Wayne Stambaugh]

1 hour ago, MoBoost said:

I’ve stayed away from additives because of the concern that they can cause deposits in the combustion chamber. I use good quality fuel (Mobil 93 octane). The valves and seats are modern materials and my valve clearances remain within spec. I’d also state that I haven’t been thrashing the car on track, so that would also be a factor. 

I might be best to start with the 93 octane unleaded and watch the valve clearances. If it seems to require frequent adjustments then maybe it is having an affect. This engine is a BDR. It came with the car in 1986 so as far as valve seats go, it has whatever it came with. Did I mention the odometer has 30 some miles on it?

[fotsyr]

59 minutes ago, Wayne Stambaugh said:

I might be best to start with the 93 octane unleaded and watch the valve clearances. If it seems to require frequent adjustments then maybe it is having an affect. This engine is a BDR. It came with the car in 1986 so as far as valve seats go, it has whatever it came with. Did I mention the odometer has 30 some miles on it?

Which means I may have sold it.

[Wayne Stambaugh]

23 minutes ago, fotsyr said:

Which means I may have sold it.

The paperwork says it came from Sevens and Elan's.

 

[Vinman1]

Been running 100LL Av gas for years in my older vehicles, never had a problem. If I could get high octane non-ethanol at the pump I would use it, but I can't (it's banned in MA). The problems I have found with ethanol fuel, is it ate the stock accelerator pump diaphragm in my Holly and QuickFuel carbs. Solved that by getting the ones for Alcohol drag cars. Then the issue is the old cars have vented fuel systems vs. the new sealed ones (loose gas cap = check engine light), and ethanol is hydroscopic and absorbs water from the air when sitting, as these old cars do. I just drained the tank and rebuilt the carb on car that would not run. I could see the water fuel separation line in the clear fuel filter! Most of the drygas additive are alcohol based and add to the problem. 

[Wayne Stambaugh]

2 hours ago, Vinman1 said:

Been running 100LL Av gas for years in my older vehicles, never had a problem. If I could get high octane non-ethanol at the pump I would use it, but I can't (it's banned in MA). The problems I have found with ethanol fuel, is it ate the stock accelerator pump diaphragm in my Holly and QuickFuel carbs. Solved that by getting the ones for Alcohol drag cars. Then the issue is the old cars have vented fuel systems vs. the new sealed ones (loose gas cap = check engine light), and ethanol is hydroscopic and absorbs water from the air when sitting, as these old cars do. I just drained the tank and rebuilt the carb on car that would not run. I could see the water fuel separation line in the clear fuel filter! Most of the drygas additive are alcohol based and add to the problem. 

One thing about Avgas, you know what you are getting when you buy it. Auto pump gas is a different story. Do you think when you buy non ethanol gas it truly is? It’s hauled in the same tankers that haul ethanol gas. Then I wonder if they even careful enough that they don’t sometimes put ethanol gas into non ethanol tanks by mistake. At the airport there are typically no options except 100LL and Jet A. Those two are impossible to mistake.

[Vinman1]

Wayne,

 

I agree, and most likely the most important part, as you said, you know what you are getting. Probably due to the potential liability of bad fuel causing a plane crash, the gas is held to a much higher standard. Rumors have been around here for years about certain brands having water their pump gas. I would not put it past them or any greased palm State inspector to look the other way! Hope your car is coming along well!

 

Vin