Quote:
Originally Posted by ArtieWag
...<snip>... As far as octane ratings, I don't have any tunes yet. And yes, when I take a long 750 mile jaunt, I do burn premium. I understand from these posts that I will even like it better than I do now after I install my tuner - Yeah! ...<snip>...
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ALL RIGHT! Now I'm understanding things a bit better. By putting "premium" fuel in your truck without being able to increase the timing to compensate, you are
hurting your gas mileage! So called "premium" gas has octane boosters in it that really do nothing more than inhibit ignition under conditions of pressure and temperature (what you get on the compression stroke) and, they cause the flame front to advance at a slower rate (slow down the burn).
Premium gas was developed for high compression engines that would cause the fuel/air mixture to ignite PRIOR to the spark (pre-ignition, or spark knock). Our engines are not "high" compression, so premium is not needed. But, the slower burn component of the fuel was designed to provide the greatest expansion at the optimum time in the power stroke, given an earlier (advanced spark) ignition point.
Without a tune, your ignition point is too late for that fuel. It is the same as retarding the spark using 87 octane gas. You lose power, because the burn is starting and completing too late. It's probably completing in the exhaust manifold, and possibly working against the piston during the upward part of the exhaust stroke.
I've said this before - "premium" gas is NOT "better" gas. The additives it contains do not contribute to the energy content.
- Jack