You can usually find tune flashes that dial in the cars computer to a specific octane. Dial in to 87. Also, a lot those really basic 'performance' mods come down to making sure obstructions in the aspiration/exhaust of the engine is reduced. This leads to modestly higher performance (usually only 3-5% gain in HP at high RPM), but also to noticeable improvements in gas mileage.
Air-box replacement and re-flashing the engine control computer have definite implications for warranty in many makes/models, so I don't endorse it.
Back when I used to fiddle with motorcycles, it was a truism- just about anything you did to make them run faster (Filter packs, Carb-modification, progressive timing advance, high-lift cams) also made them run more efficiently as long as you did not draw on that increased power. My rpm's at highway speed on my last bike were absurdly low. Even though todays cars run with EFI and Mass Airflow sensors, I'm sure the same basic ideas hold. The more you get out of each rpm and each drop of gas, the more power and more efficiency you will get.
Yeti
Off Topic » in reply to 5 mpg more.
Re-Tune