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

[Alexei Pavlov]

bill.shurvinton at nokia.com wrote:
> 
> Try searching for 'miller cycle' you get
> 
> http://www.howstuffworks.com/question132.htm


Thank you guys. The miller seems to rely on a compressor
to avoid the incoming air exits the cylinder.

I think my initial question 'Why there are no pumping losses with
variable valve lift' was not precise enough. This has led to
an interesting discussion, although I still want to understand
intake pumping losses :-)

In fact 1-2 month ago I read an article claiming
that the new BMW variable lift system ('Valvetronic' I think)
gets rid of intake pumping losses. And didn't see why.

These engines are indirect injected. I don't know if they
use EGR to fill the chambers (for some loads).
BMW claims a 10-15% efficiency gain (this is certanly true),
and the article claims it's partially thanks to variable lift.

I agree that the absence of the trottle removes some losses.
But valves still perform the same job: prevent the air to fill
the whole cylinder volume. I agree that such a system can
improve swirl and air speed at the valve level, but I still
don't understand why the piston has no more job to do to
pump the fresh air.

Sorry if I'm slow to understand simple thinks.

Alexis

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