AvGas is for Airplanes

AvGas is for airplanes.  Airplanes fly at altitudes with lower air pressure than is common at ground level.  The lower air pressure makes it easier for fuel to evaporate.  Having all the fuel evaporate through the tank vents before an airplane reaches the next gas station can be kind of a drag.

AvGas was tits after WWII when it was higher octane than street level gas.  That was a long time ago.  Back then AvGas had significantly higher octane than otherwise available.  This made it work well with high compression engines, which racers liked.  The gas companies have since developed higher octane fuel for surface level use, including developing race gas.

They make AvGas with what is called Low Vapor Pressure.  That makes it work fine at airplane altitude and not so fine at ground level.  As in, hard to start.  Also making less power since more gas is passing through the system as unevaporated droplets.

My personal experience which led me to this truth involved a Triumph TSS (stock 8 valve head, last model the old Triumph ever released) that I raced a couple of times in the AMA Battle Of The Twins Class.  I was stepping up to the National level so did everything I could think of for that bike.  Including pre-race pilgramages to the local airport.

That bike used to wear out three pushers (removed the kick start mechanism) before starting in the morning.  Finding a fourth pusher after people had seen three of them wear out was kinda difficult.  Then one day I got behind schedule and couldn’t make it to the airport.

So I bought the race gas for sale at the track.  The bike started the _first_ time I dumped the clutch.  I never bought AvGas again.

AvGas is for airplanes.