[Diy_efi] Intro, and q's about fuel economy

[Greg Hermann]

At 4:10 PM 12/16/02, Alexei Pavlov wrote:
>> Using the valves to throttle the flow has different effects on the
>> flow. It's still throttling; i.e. restricting.
>>
>> The main difference is that with variable lift, that the gas flow
>> speeds through the valves is higher and this results in greater
>> swirl and filling of the chamber.
>>
>> Further; the flow upstream of the valve is unthrottled, so it's at
>> atmospheric pressure or greater, even when not supercharged. In
>> essence, the vacuum the piston has to draw is out of a smaller
>> volume; the cylinder itself instead of the whole inlet tract.
>> (A bit of a simplification, but it helps to draw the mental
>> picture.)
>
>I would say that pumping from a large volume is easier than
>from a small one. Am I wrong ?

What you are missing is that there is an irreversible loss when the flow of
a gas is throttled. Doesn't matter whether the throttling process occurs at
a throttle butterfly or at the intake valve--the pumping loss occurs when
the gas in the cylinder must be compressed back up to atmospheric pressure
in order to go out through the exhaust system.

Greg



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