Better fuel economy when chipped (Myth or Fact)

[Ryephile]

During part-throttle there's technically no difference as your car is switching around 14.7:1 AFR. However at WOT, since you should be running around 12.0:1 versus the 10:1 of stock, you'll get marginally better mileage. The net effect on your whole tank around town however, will be virtually nothing.

Now, improved power via more ignition timing advance will improve fuel economy at all load points. Most aftermarket ECU "chips" love to crank up the ignition, and based on that, you may see a minimal gain in MPG, perhaps a tenth or two, just a guess.

Cheers,
Ryan