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Newer gas in an older engine.


Guest FourDoorBoris

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Guest FourDoorBoris

Hi all!

Back in September, I purchased a clean 3 owner 1969 Buick LeSabre that hadn't been driven since 1995. Its a great running car and I try to drive it as often as I can, problem is it's rather expensive to run because I was told I have to use hi-test (93 octane) gas in it. It has a 350 with a 4bbl Rochester Quadrajet. I've been putting in some lead additive as well since it never has been converted. It takes 85 bucks to fill the tank typically and I was wondering if there was any cheaper way to fuel my car? Will typical 87 or 89 octane work in the engine or will it cause it to knock? Would it be cheaper to fill it with 87 and use an octane booster? Or am I just gonna have to keep putting in hi-test gas? I'm 17 years old so my budget is rather limited. Thanks!

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The only way to know if lower octane fuel will work is to try it. A single tank won't necessarily tell you, as there will be some residual higher octane fuel mixed with it. If you detect pinging or detonation, then the answer is no, you need the higher octane. The 350 2bbl engine was 9.0:1 compression and should be fine. The 4bbl engine was 10.25:1 and will require the higher octane. I doubt you need the lead additive. First, your engine has a lifetime of lead deposits built up on the valves already. More to the point, the lack of lead will only mean that you'll need a valve job in 80,000 miles instead of 100,000 miles. As for the cost of gas, unfortunately, that's the price of admission to this movie. Get a four cylinder beater as a daily driver and save your gas money for nice days in the Buick.

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What is your compression ratio? If it is a standard engine (not high performance) it should run fine on regular. If it knocks a little, you can back off the ignition advance a little. This will reduce your gas mileage and power so, is the kind of hack you only use if you have no choice.

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