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      05-11-2020, 01:16 PM   #136
pbonsalb
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Drives: 18 F90 M5, 99 E36 M3 Turbo
Join Date: Feb 2011
Location: New England

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I know the on board computer in my E36 does not compensate for larger injectors, so it looks like mpg is better because pulse width is reduced and it thinks injectors are stock. I assume car computers have gotten much smarter.

If you are actually making significantly more horsepower, you are using more fuel. It’s roughly 1/2 lb per hour of fuel to make a horsepower. If you are making 100 more hp, your fuel use will be up. But if you are just cruising and making no more power than stock, it may well be that you get about the same mpg and maybe even slightly better due to the tune or reduced exhaust back pressure if part of the exhaust was changed at the same time.
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