Re: Air filter interval and fuel economy... - Saab 9-5 Bulletin Board - Saabnet.com
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Re: Air filter interval and fuel economy...
Posted by Dean (more from Dean) on Wed, 6 Feb 2013 08:51:43
In Reply to: Air filter interval and fuel economy..., Mark from Toronto, Wed, 6 Feb 2013 08:35:44
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You are making MPG's mostly on partial throttle. That means a pressure drop to the intake manifold. Most of that is at the throttle body and some from pressure losses in the rest of the intake system. If there is a slight increase in pressure drop across the intake air filter, the throttle body then would be lightly more open and nothing really changes. Dirty air filters do not decrease MPG's despite what you see on TV ads for car parts.
As for open throttle performance, the ECU controls mass air flow and will compensate for some increased resistance in the air filter by closing the wastegate slightly more. Time to get on full boost might be slower in some cases. Closing the wastegate more does increase exhaust manifold pressure and such increases directly reduce torque for any given air-mass flow. And making the turbo work harder has a compound effect because the air is heated more, hotter air at a given mass air flow means higher velocities and larger pressure drops in the ducts and IC that must be compensated for. Hotter intake air also can cause the spark advance to be further retarded and/or "fatter" enrichment.
posted by 65.71.16...
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