Fueling Up And Methanol Madness
I would like to know how much methanol I need to add to 91-octane pump gas to keep a 12.5:1 compression ratio motor from detonating. Some Midget racers from the '50s and '60s informed me I need to use amyl acetate to get it to blend properly with the gasoline.
My specific questions are:
1. What ratio of methanol to gasoline do I need?
2. What ratio of amyl acetate do I need? The Midget racers said 1 percent.
3. Will I need to change jets?
4. Where can I purchase amyl acetate?
5. What will happen if I do not add the amyl acetate?
Charles J. Palmer
Golden, CO
The first thing that comes to my old feeble mind is why are you going in the direction you are going? My second question is why don't you just use 100 percent methanol? That's what many of the old guys ran in the '40s and '50s. Your engine will make more horsepower on methanol than on gasoline, although it will require about 1.7 times as much methanol as gasoline.
Having said that, let me go back to your first question about how much methanol to add to 91-octane gasoline to satisfy your 12.5:1 compression ratio engine. This depends on the octane requirement of your engine. The octane requirement depends on many things, compression ratio being one. Other things that determine octane requirements are bore diameter, cylinder-head material, coolant temperature, spark timing, intake air temperature, humidity, barometric pressure, and altitude.
With a 12.5:1 compression ratio at your location in Colorado, you do not need much octane because of low cylinder pressure resulting from low barometric pressure/high altitude. The second choice instead of 100 percent methanol would be 90 percent gasoline, 5 percent methanol, and 5 percent tertiary butyl alcohol (TBA). The TBA works as a cosolvent to keep the methanol in solution. Amyl acetate will probably do the same thing, but we are trying to provide you with technology from 1999 rather than 1950. Methanol and TBA can usually be found at a chemical supply company or racing-fuel distributor.
You will need to change jets in the carburetor. For 100 percent methanol, the area of the jet should be at least 1.7 times as large as for gasoline. If you go with the 90-5-5 mixture, an increase in jet area of 10 percent should get you in the ballpark.
Hope this helps you.
Tim Wusz
76 Performance Products