Quote:
Originally Posted by JARblue
And this is why everyone gets worse gas mileage after a new exhaust install despite the fact that a freer flowing exhaust should get better gas mileage all other variables being equal.
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Only true at light throttle / load.
At full throttle you have more airflow, which means more fuel gets injected, and your economy will be worse. Often, because you're flowing more air than a stock car, you hit new map cells that are tuned very conservatively because the stock engine doesn't normally go there. Those cells are usually richer and more retarded than normal, which also hurt economy.
Unlikely to happen in an NA car where bolt-ons are only worth a few percent but turning up the boost in a 90's turbo Nissan absolutely does this "Rich & Retard" effect on the stock ECU.