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post #8 of (permalink) Old 01-16-2000, 04:17 PM
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Re: 93 octane in stock engine

That's right, higher octane burns slower (or rather, later) than lower octane fuel, which prevents detonation in higher compression engines. If you're not getting detonation (knocking, pinging) on the lower octane fuel, higher octane fuel will do absolutely nothing for you except empty your wallet faster (no small matter considering a Jeep's crappy mileage). In general, the higher the compression ration, the higher octane required. However, some modern computer controlled engines (dunno if any newer Jeeps fit in this category) have a "knock sensor" that will retard the timing if it senses detonation. In this case (only), you won't hear any pinging, but there will be some power loss as the engine adjusts itself to the cheaper gas.

OTOH, some cars ('70's Fords in particular) would be pinging all the time no matter what fuel you fed them. It was annoying, but normal and expected.


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