Aviation Fuel

[Marian Claire]

7: As to your second question. I believe the problem with some marina gas is it is not a high priority item for the marina. It can be old and the tanks and filters can be poorly maintained etc. The neighborhood store goes thru much more gas so at least it is fresh. I have used my marinas gas with no problems but they maintain the system and it is non-ethanol. Dan S/V Marian Claire
Edit: The gas at the marina is also blended with stabilizer. I think it is "valvetech" fuel.

[Ball Racing]

The compression ratio is so low in the A4 that it will never see the benefiet of the extra octane.
92 octane is really almost too much.
But yes, try to get the ethanol free gas.

[kiskadee]

A low compression A-4 is wasting fuel if run on anything above Regular octane. Higher octanes burn slower and are much less prone to detonate (pre-ignite) in high compression engines. On an A-4 the spark plugs are not centered above the cylinders. It needs lower octane fuel to flash across and ensure a complete burn. Higher octane fuels would still be igniting long after TDC, with a loss of power and unburned hydrocarbons going out the exhaust. Even a much richer mixture of Avgas would not achieve the same power as Regular gasoline. Avgas costs considerably more than Regular gasoline.

Avoiding the "food vs fuel" arguments of ethanol, it's main problem in a boat is that it can absorb water vapour out of the air. Automobiles use a sealed system. Boats have open vent hoses that allow moist air to enter as the tank breaths with heat and cold. The extra water that builds in un-sealed fuel tanks can cause problems in some high tech carbs or fuel injection systems... But I doubt that the A-4 carb would mind.

I don't think the A-4's suffer from a lack of lead in their fuel, but it may be a moot point as the Aviation people are working on removing lead also.

The question that opened this thread has different answers on our Atomic-4's than it would on a high-tech marine engine. The high tech modern marine engines don't want extra water in their fuel, so they should keep their tanks full at all times when not in frequent use. However, the Atomic-4, the environment, and our fuel-budgets all prefer the lower octane.

[P30]

I just filled up my tank with premium hi-test ..

"It needs lower octane fuel to flash across and ensure a complete burn"

geez, am i gonna hurt the thing?

[67c&ccorv]

I want an engine that will work on methane distilled from human excrement...

- forget the AV Gas solution...go with the fuel that you will find at the end of the earth with no other solution.

[Laker]

P30 - you will be fine , just do not waste your money on high octane on the next fill-up. You could reduce the octane value of the fuel in your tank by blending in a couple of gallons of lower octane fuel via gas can after you have burned some off , if that would ease your mind.

Corv - "fuel that you will find at the end of the earth ..." - Congratulations , you have stumped the panel.

[prstack7]

In my area, regular is 87 octane with 10% ethanol. mid-grade is 89 with no ethanol, and premium is 92, no ethanol. Would mid-grade work well?

[joe_db]

I could tell exactly NO difference in how the engine ran when using 100 LL avgas.

geez, am i gonna hurt the thing?