Using Aviation Fuel In Your Mopar

[Cranky]

I run 91 regular pump gas in an 11:1 engine without issue ever. Sounds to me like these old iron engines really have a heat soak and head chamber design issue possibly which drastically effects their pre ignition. Octane doesn't add power. It just make the flash point higher is my understanding. Yes if you are having issues with detonation and add more octane is should help the problem.

What's the specs on your cam and what's your cranking PSI. You can run cast iron heads etc with 11-1 static compression but you will also need a cam that will bleed off cylinder pressure in the lower rpm ranges for it to work without ping issues. Having a good quench will also work in your favor along with several other items in the combination. Keeping a high compression engine cool will also help towards that goal.

As for the avgas, it only took 1 gallon to a tank of 93 octane to keep my 71 340 Cuda running good but 93 would also run fine so long as my temps stayed 180 or less but in Texas, that isn't so easy to do, and yes, I usually ran my timing up a bit from factory settings. My initial was always around 12-15 on that car.

For long term storage...why spend so much on avgas when you can use pump gas and double dose it with marine Sta-Bil? Been doing it that way for years now and then in the spring, you can just drive easily until you burn some off then add the avgas for full throttle fun.

 

[J5 GTX]

I've always understood that AVGAS is not a great alternative for cars because it's designed to run - as you'd expect - at high altitude. I tried it in my 68 RR many years ago and it didn't make one damn bit of difference. But in those days pump gas was not what it is today. I suppose if you have good results then motor on, but it wouldn't hurt to do a little chemistry research.

If you didn't adjust your engine to take advantage of the higher octane, there won't be any difference. Maybe, less performance as someone mentioned earlier.

Other than octane, the key is the Tetra-ethyl Lead. As we all know, those pre-'75 Mopar engines need lead for longer valve life.