What grade fuel?

[cdlongjr]

The PO old me to use Hi test. I know from my garden tractor pulling days that even with a highly modified engine, I only had to use regular. I'd like to know what grade ya'll are using in a stock AMC 258 i6 / 4.2l . AMC 258 i6 / 4.2l CI.

 

[CJ]

Don't waste your cash on premium. Your CJ was designed to run on regular fuel.

 

[LongHorn]

Sounds like the PO was running to much ignition advance, or to low shift points.

 

[hole]

If your AMC 258 i6 / 4.2l is injected you may need to run premium. My 8 has MPI and has to run premium and still pings occaisionally.

 

[BrockGrimes]

A little info on gas most people don't know.
regular- easy to ignite
mid-grade- less easy
premium- hardest to ignite

The reason you run premium in performance applications is to prevent pre-detenation, due to the heat created during compression.
If your running the stock compression reguardless of the fuel source (carb, TBI, MPI, TPI) all you need is regular if that was what was stock for that motor.
Now if you raise compression, then you might want to start bumping up your octane.

"Now where did I put that flame retardant suit?!?!"

 

[LongHorn]

Cam Shaft & Ignition timing also play a part in a true compression ratio.

 

[cdlongjr]

Thanks guys!