a technical discussion, engine efficiency |
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a technical discussion, engine efficiency |
r_towle |
Aug 15 2005, 08:27 PM
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#1
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Custom Member Group: Members Posts: 24,624 Joined: 9-January 03 From: Taxachusetts Member No.: 124 Region Association: North East States |
so, I have been thinking (not always a good thing)
If an engine is basically an air pump, and the objective is to make it as close to 100 percent efficient, why is the exhaust valve so much smaller than the intake valve? Forget emmisions, forget fuel delivery, just want to understand why this is so...it is so on most engines... Rich |
messix |
Aug 15 2005, 10:06 PM
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#2
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AKA "CLUTCH KILLER"! Group: Members Posts: 6,995 Joined: 14-April 05 From: between shit kickers and pinky lifters/ puget sound wa.north of Seattle south of Canada Member No.: 3,931 Region Association: Pacific Northwest |
the exhaust is at very high pressure after ignition, therefore not as big of valve or port is needed due to the high velocity of the hot gas. the intake can be larger to assist in better flow and velocity. there is a balance between the intake and exhaust that is about 80% of exhaust flow to intake flow. this is measured on what is called a flow bench, this draws air thru the desired port at a standard barametic pressure in inches of mercury and the measurement is given as "CFM" much air has moved thru the port in a give time. the higher the number the more air.
this is the general basic for n/a engines, when any type of forced induction is applied things get much different. |
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