Gas mileage with gen III intake

Modshack

Welll....You're not "really" running rich under everyday partial throttle driving conditions. While the ECU is calibrated slightly rich, the O2 sensors, in concert with the MAF are constantly adjusting the fueling to maintain a stochiometric 14.7:1 ratio no matter what intake you have. This is Multiplicative adaptation otherwise known as long term fuel trims or closed loop. The sensors determine the Correction (injector duration) that needs to be applied to maintain the correct A/F ratio. The "Rich" 370 typically runs at -9 to -12% rich correction which means the fuel is dialed back to keep A/F's good. An efficient intake will result in lower numbers here but they are still "Corrections" with the desired goal of a Stochiometric A/F. The end result remains the same. These numbers (fuel trims) are easily read with a Scangauge or equivalent. When you go to WOT, you leave 02 fuel controls behind and go to pre-built fuel maps. These are typically a bit rich, but with the right intake you'll flow a bit more air to so it balances well. YOu're still using X amount of fuel, but with more air and a slightly leaner WOT mix you make more power. The real HP gains are made at high RPMS under WOT open loop conditions where More flow tells the MAF to deliver more fuel ...So technially, even though you are a bit leaner at WOT, you're really burning more fuel due to flow improvements read by the MAF. This is where the Dyno'd improvements are coming from. More air + more fuel + slightly leaner mix = more HP. Still no free lunch. Anyone who spends much tme with their foot in it can verify that.. You really have 2 distinct fuel usage profiles here. If you never step into it and make that transition from closed to open loop (determined by RPM, Engine load and throttle position) it should be a wash mileage wise, but you're not making any more HP in those ranges either.

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