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Old 03-10-2011, 06:40 AM   #15
bal00
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Join Date: Feb 2004
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Quote:
Originally Posted by amanichen View Post
The more closed the throttle is, the lower the pressure in the intake is, and the greater the pressure differential between the inlet and outlet of the engine. Maintaining a greater pressure differential requires more work, and therefore requires more fuel.
Yes, that's why gas engines are not terribly efficient at part throttle, but where that pressure drop occurs makes no difference.

If you need an engine to produce say 25 hp to maintain a certain speed, you need to burn a certain amount of air and fuel.

If you remove an intake restriction (such as a very dirty air filter) and keep the throttle where it is, the engine will pump more air, inject more fuel and produce more power. That means you now have to close the throttle a bit further to reduce the air flow back to the old level so you can maintain your speed. In other words, the pressure differential will be exactly the same.


If what you're saying was true, you could improve your gas mileage by drilling holes into the throttle plate (removing an intake restriction). In reality this will not help fuel economy at all, it will just change the pedal position needed to produce a certain amount of power.
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