I am just curious on what is the best gasoline to use in a 1968 GT? The engine has been rebuilt and is 30 over… Everything else is stock except the Pertonix Ignitor. Equipped with A/C as well.
I can and have been using Premium 93 with up to 10% ethanol and this seems to work fine with no pinging. Non ethanol gas is available but it seems to be only 90 octane around here. Would this work as I think non ethanol gas would be better for the engine.
That topic was just discussed - see above link. Does it ping with 90 octane?
I haven’t tried using the 90 octane non ethanol gasoline in the GT 390 so I don’t know if it will ping. The 390 engine has a 10.5:1 compression ratio which seems to me that the 90 octane of the non ethanol gas would be too low. I saw the post about 90 octane non-ethanol but it did not mention if higher compression ratio engines could use that lower level of octane. If I remember correct, the premium gas in the late 60’s and even early 70’s were probably 99 or 100 octane as compared to the 91 to 93 available today. (not sure this is a proper comparison as the fuel then was only rated using the research octane number where as today the rating is different ( research + motor/2 ) In addition, the price per gallon of non-ethanol gas is roughly $4.59 per gallon in N. Georgia. I was wanting to know more before trying a complete fill up…
Others with that engine may have better info for you. But my 70 351C 4V with 11:1 compression ratio runs great on 91 octane ethanol-free with timing set to factory spec.
Edit: I should add that mine did ping badly on 91 octane before I fixed the overheating problem and cleaned out the combustion chamber carbon deposits.
My GT-E 427 has a 10.9:1 compression ratio (stock) and it pings horribly on 92 octane Super Unleaded. It loves 110 octane leaded race gas so that is what I feed it.