Premium Gasoline ?

[Mr. Prop-B-Gone]

Octane is a measurement of how explosive the gasoline is. The higher the octane rating, the less explosive the gas is. Higher octane prevents preignition. As the Gas/Air mixture is compressed in the cylinder it heats up. The higher the compression the hotter it gets. If it gets too hot it will ignite before the spark plug fires, and cause engine knock, which will damage engine bearings and burn holes in piston heads.

Octane is not a measurement of the energy contained in the gas, so a higher octane does not provide more power or better gas mileage. If your car or boat engine sounds like it's full of marbles, especially if you are in 4th gear going up a hill or accelerating hard, your engine is knocking and moving up to a higher octane will probably help. If it doesn't, have your engine timing checked.

Other than that, you should use the octane level your car or boat engine specifies. Using a higher octane will not provide you with any benefits, but it will make the oil companies richer!

Haven't seen it in NH, but in Florida many of the gas stations advertise no ethanol gasoline for boats.

[BroadHopper]

The more advanced engines today not only burn cleaner but provide better mileage. MBs, BMWs and Audis requires 91 in the states, more in Europe. The ECM compensate for lack of high octane in the states. I was told by other European performance car owners that they notice a difference if they find higher octane gas.

The new 4 cylinder, turbo engines provide as much HP and torque as the old small block V8. They do require higher octane to prevent knocking, especially when the turbo kicks in.

I read somewhere that there will be a demand for 91+ octane in the future because of the strict emission as well as gas consumption regulations. This will cause the refineries to produce higher octane gas and hopefully the price will go down. Today the refineries are not producing enough high octane gas so the prices are high.

[Dave R]

Originally Posted by Mr. Prop-B-Gone

Octane is a measurement of how explosive the gasoline is. The higher the octane rating, the less explosive the gas is. Higher octane prevents preignition. As the Gas/Air mixture is compressed in the cylinder it heats up. The higher the compression the hotter it gets. If it gets too hot it will ignite before the spark plug fires, and cause engine knock, which will damage engine bearings and burn holes in piston heads.

Octane is not a measurement of the energy contained in the gas, so a higher octane does not provide more power or better gas mileage. If your car or boat engine sounds like it's full of marbles, especially if you are in 4th gear going up a hill or accelerating hard, your engine is knocking and moving up to a higher octane will probably help. If it doesn't, have your engine timing checked.

Other than that, you should use the octane level your car or boat engine specifies. Using a higher octane will not provide you with any benefits, but it will make the oil companies richer!


Haven't seen it in NH, but in Florida many of the gas stations advertise no ethanol gasoline for boats.

If the owner's manual of your modern (anything with a knock sensor) car says to use premium, the engine will likely run at reduced power with low octane fuel. I agree with you, it's not because the low octane fuel contains less energy, it's because spark timing needs to be retarded to keep the combustion chamber temperature lower to prevent pre-ignition. There is nothing you can do to adjust timing manually on these engines, the ECU will take care of that automatically.

If an engine was designed to make use of high octane fuel, the ignition timing will be set such that peak combustion chamber pressure occurs at the same time that the connecting rod can apply the most leverage (for the longest time) to the crankshaft. If you retard the timing to reduce the heat generated, you reduce the time that the combustion gases push down on the piston and that reduces power.

The 5.9 liter V8 in my old 99 Dodge had modern electronics, but no knock sensor. The timing was set such that it ran fine (occasional light spark knock) on 87 octane with no load, but if I was towing, it would knock and ping like crazy. For towing season, I always filled it with premium and I swapped out the 192 degree thermostat for a 180 degree. Despite having a normal distributor, you cannot alter the timing on these 5.9 engines. The computer will just adjust the timing to whatever it's programmed to regardless of the distributor position.

You can get ethanol-free boat gas in VT and NY. In my experience, it's more common than E10 at marinas there.

[Rich]

If you want 93 gas, I just saw some yesterday at the Shell station at exit 20 in Tilton.

[Lil' Barndoor Guy]

Goodhue& Hawkins has 93 octane with Star-tron additive to deal with the ethanol. It's only $2.99 per gallon this year.

[Woody38]

Cobalt I believe you are correct in that AV 100LL is low lead.
Sorry for the misinformation I put here.

[Cobalt]

The lead in the fuel is better for older engines providing valve lubrication. I use AV fuel in an older car for this reason, and the increased octane.

Who knew we would buy fuel from an airport for our older boats and cars?

[Outdoorsman]

I don't generally pay attention to the octane levels in fuel, but today I gassed up at an Irving Main Way and their premium was 93. Since the OP was not on the lake (or posting about octane available ON the lake) I find this relevant.