Re: Efficient Engines

[Luis Marques <marques@xxxxxxxxxxxx>]

> From: Neil Deshpande <deshpand@domain.elided> 
> 
> Instead of having the throttle butterfly valve control air flow, the
> engine uses variable valve opening.....
> 
> Efficiency is increased by eliminating the butterfly valve's
> restricting presence. 

I read something about this somewhere not too long ago.  Although the
design could potentially be more efficient, the absence of a throttle
butterfly will only give a tiny bit more power at WOT (and then only
maybe 0.5%).  At any other time you are simply moving the restriction
from the throttle to the valves - you still have the pressure drop.

Where there could be a small increase in efficiency is at part throttle,
due to the lower effective reciprocating mass since the valves only have
to move back and fourth a minute amount.  Reciprocating mass losses go
up with the square of the velocity, which is propotional to the
displacement at any given RPM.  Put another way, a higher lift camshaft
zaps more power out of the engine than a smaller one because the valves
have to move further while opening and closing. 

Luis Marques
'97 328i

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