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Old 06-02-2010, 12:05 AM   #61
Dirt, Sweat & Gears
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Joined: Jul 2004
Location: Houston, Texas
Oddometer: 442
Originally Posted by The Griz

14.7:1 is known and has been known for decades to be the perfect air/fuel mixture for gasoline-burning engines.
No such thing as a perfect air/fuel ratio.

14.7:1 is the ratio that has a Lambda of 1. That means you thoeretically have exactly enough air molecules to burn all the gasoline molecules. That is what the EPA thinks is perfect because it produces the least emissions.

A slightly lean mixture - 15.4/1 - generally gives the best fuel economy.

A slightly rich mixture - 12.6/1 - generally gives the best HP.

I have read that a bit leaner - 13/1 - produces the most torque.

Also leaner engines run hotter and therefore are more prone to pre-ignition, ie knocking.

Richer mixtures run cooler and most likely add to engine life.

Also a flat air/fuel curve is not necessarily the best although it does give the smoothest, most predictable power delivery, however it would seem to me that an Air/fuel curve that starts out at about 13 or a bit higher/1 and then decreases to about 12.5/1 over the RPM range would give the best torque in the lower RPMs and the best power in the upper range. This would cost you in fuel economy but I am willing to give up a bit of economy for a bit more power.

Plus this entire discussion is for pure gasoline/air ratios. Gasoline additives change the analysis and every vehicle has to be tuned on a dyno with the fuel it is going to run to obtain optimum results.

And finally, all of this is for normally aspirated engines and forced air induction engines (turbocharged) should be run richer still for both optimum power and engine life.

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