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Old 03-10-2011, 01:13 PM   #23
bal00
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Member#: 54772
Join Date: Feb 2004
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Quote:
Originally Posted by amanichen View Post
You're confusing the operation of a modern fuel injection system with energy required to pump air.

All engines are air pumps, regardless of how much fuel is added. Maintaining a smaller pressure differential across a pump requires less work and less energy. I don't know how else to put it

Again, the energy spent pumping air through the engine is a small fraction of the total energy used by an engine.
I'm not confusing anything.

If you reduce the overall pressure differential by getting rid of on an intake restriction (such as a dirty air filter), the driver will simply lift the throttle and restore the original pressure differential. That's how part throttle operation works.


This it how the picture looks with a dirty air filter:

Atmosphere(1bar) --> dirty air filter(-0.1bar) --> partially open throttle (-0.2bar) --> engine (0.7bar abs.) = 35 hp output

Now you replce the dirty filter with a clean one:

Atmosphere(1bar) --> clean air filter(-0.0bar) --> partially open throttle (-0.2bar) --> engine (0.8bar abs.) = 45 hp output

Now the driver would go "wtf, I didn't ask for 45 hp" and lift the throttle because the driving situation only requires 35 hp, and it would look like this:

Atmosphere(1bar) --> clean air filter(-0.0bar) --> partially open throttle (-0.3bar) --> engine (0.7bar abs.) = 35 hp output


The overall pressure differential is exactly the same as it was with the dirty filter, and so is the air flow, the fuel consumption and the power output.
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