Must I put premium gas in my 1965 Ford F100 390 V8 or can i put regular gas?

I was told that it needs premium gas and premium gas only. But the guy who I bought the truck from said it was a myth and it takes regular gas. What gas does my Ford F100 390 v8 engine take!?

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  • 7 months ago

    If it has a 390 then it's anybody's guess, I don't think they put a 390 in the F100 until 1967. So you probably got either a 352 or swapped motor. My guess is it's a 352 2V (two barrel), 8.4:1 compression— 208 horsepower.

    The last one I had ran ok with 88 leaded. I would personally run 89.

    BTW Backfiring means unburned fuel is getting into the exhaust. You have an ignition failure or a bad exhaust valve. Nothing to do with octane.

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  • 7 months ago

    If it is non pinging, then regular is fine.

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  • 7 months ago

    If it's the original engine (F-100's could have a 390 2 barrel), then it's a low compression version 8.2:1 or 8.5:1 depending on the year. Those engines could be run on regular fuel without issue and should run on 87 octane just fine. If the engine is not original ( if it has a 4 barrel, then it's was probably swapped in at some point), then you will need to run premium fuel. Those versions had 10:1 compression or higher.

    Either way though unless the valve seats have been replaced with hardened ones, you're going to get some erosion and the valves will no longer seal correctly, and you'll lose compression. It's one of the side effects of running unleaded fuel in an engine designed for leaded fuel. If the valve seats have been replaced then you should be fine.

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  • 7 months ago

    Try a half tank of regular just to see if it knocks or pings. If it does, fill the rest of the way with premium. That engine was build originally to run on leaded gasoline, which is no longer available, so unless the heads were upgraded with modern valves and seats, your 390 probably doesn't run well and smokes. Those old 390's had 10:1 compression ratio, so i wouldn't even try to run it on lower than premium fuel today and in 1965, premium was 100 octane.

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  • 8 months ago

    That old of a vehicle needs only to have its timing adjusted to take care of octane problems

    • The Devil
      Lv 7
      7 months agoReport

      yop, and lose 40 HP

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  • Ron
    Lv 7
    8 months ago

    Premium gas in not required

    • The Devil
      Lv 7
      7 months agoReport

      Save $2 on a fillup, then spend $5 for a bottle of octane booster to relieve the engine knock. No reason to buy premium. Could set back the timing a few degrees and sacrifice HP for no knock, but increase HC and CO emissions.

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