| :If you could get your filter dirty enough to seriously restrict flow (actually cause drag on descending pistons), your engine would become less efficient...at WOT. ok...not what I would consider a realistic scenario though :At anything else, you're already restricting the engine, except you call it "throttling". Probably back in the day people misinterpreted their low mileage due to richness as due to intake restriction, and that's how the myth came to be. But restricting airflow via dirt isn't much different from restricting it via a metal disc. No. Throttling with a dirty air filter is much different than throttling with a throttle body on older cars, in that the dirty air filter causes a similar effect as applying the choke
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