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post #1 of 5 (permalink) Old 07-21-2018, 10:58 PM Thread Starter
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Basic Questions

I have inherited a 66 GTO. It is fully restored and has been meticulously cared for. I am new to the classic car world and have a very basic question. what do I do about fuel? I know ethenol is bad and I should use premium and a lead additive. However I can only get 89 octane ethanol free here. So should I use that plus the lead additive or use the premium with ethanol and the lead additive?
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post #2 of 5 (permalink) Old 07-22-2018, 09:07 AM
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Since you probably won't be driving it much, you can go with the E-free gas & add some Torco Accelerator octane booster. Or, you can mix in a little racing gas. The booster is easier. It cost just over $20 per quart.

Torco unleaded accelerator, it is not just another octane booster

Most say lead is not necessary, especially for light duty driving. Even back in the '60's & '70's, we used AMOCO "white gas" in our Musclecars. Never heard of any problems it caused.,5208280&hl=en
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Last edited by bigD; 07-22-2018 at 09:39 AM.
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post #3 of 5 (permalink) Old 07-22-2018, 02:22 PM Thread Starter
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I have read that without the lead additive the engine may knock
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post #4 of 5 (permalink) Old 07-22-2018, 09:35 PM
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Originally Posted by Tallmike View Post
I have read that without the lead additive the engine may knock
Keep in mind that the advertised compression was not the actual compression. Pontiac advertised 10.75 and 10.5, but this was with minimum volumes of the head's combustion chamber. The heads were generally more than the minimum and you had to mill them to get there.

You may or may not get the "pinging" or "detonation." The lead in the old gas was a lubricant for the valves as well. You can add an additive as bigD suggested or mix some racing gas in with the pump gas. You also may be able to adjust timing to get rid of the knock. Retarding the timing and/or changing the advance curve may work and you can still use the higher octane pump gas - but you can only retard timing so much as it will begin to run hotter, and you will be giving up engine power.

On ethanol, your engine may also run leaner and you may want to change the jets in the carb by going up a few sizes to richen it up a bit. Other things you can do is make sure your cooling system is in top shape, fan shroud installed, good fan(either factory clutch fan set-up or aftermarket flex fan), a 160 or 180 thermostat, and you might want to try one step colder spark plugs. Minimize the heat in the engine and it will help with the gas situation.

The problem with ethanol is that it goes bad quickly if not used up, absorbs water, and deteriorates the "old type" rubber hoses and even the needle tip in the carb if so equipped. Non-ethanol gas will last a lot longer if your car sits. With a gas stabilizer, it can be good for over a year or more from what I read.

So, I don' think anyone can give you an exact formula to use when selecting what gas to run - you may have to experiment. However, what you don't want is to allow the engine to "knock" "ping" or "rattle" as this will destroy an engine if allowed to go on for long periods of time. This usually happens under heavy throttle or under load and can be more common on really hot days as heat can contribute to the "knocking" or "pinging." If you do experience it, then back out of the gas so it stops. Then make your adjustments in either gas mixtures/additives and/or timing changes.

So it will be something you will have to play with. If you ever have to rebuild the engine, then you want to get pistons that will give you around a 9-to-1 compression ratio with iron heads and you should not have to worry about gas octane choices.
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post #5 of 5 (permalink) Old 07-25-2018, 04:10 PM
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I've been unsuccessful in driving stock compression '65-'67 GTO's in CA on pump gas without detonation for the past 30 years or so. With my '65 GTO, I run Octane Supreme 130, which is a booster that has tetraethyl lead. In your case, I would run the 89 non-ethanol fuel and mix it with the Torco or the Octane Supreme 130, which are the ONLY 'octane boosters' that will actually work in a pre-packaged, ready to use form. Some add other chemicals to the mix with varying results (Tuluene is a great booster, but $$$) . You can add race gas from the speed shop, too. I ended up dropping the compression on my '67 GTO, and it runs ok on 91 octane e-10, which is all I can get in CA. With your car, and your situation, it would be in your best interest to not modify the car and to simply upgrade the octane, by hook or crook! Good luck, and welcome to the forum.
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