New Saab Engine Tech

[Bernd Felsche]

steve ravet writes:
>Believe me, that engine rarely suffered from "pumping losses".  I've
>also heard plenty of times that the more vacuum you have the better your
>fuel economy is, despite the fact that vacuum=pumping loss.

Fuel consumption by itself is not a good indicator of engine
efficiency.  If you combined fuel consumption with average speed,
and distance then you get a better indicator.

"Fuel economy" has many meanings; to some it's just the amount of
fuel consumed. You can reduce the amount of fuel consumed
drastically by throttling; but would you rather consume 5
litres/100km at 50kmh, or 8 litres/100km at 120kmh?

The best engine efficiency in an Otto-cycle engine is achieved with
no throttle at an engine speed yielding maximum torque (BMEP).  If
that gives you way too much power for what you're trying to do, then
the engine is too big for the job.

If it doesn't give you enough power, then you are also off peak
efficiency as you have to rev the engine faster to get the required
motive power. The reduced BMEP at higher engine speeds indicates a
reduction in efficiency, often related to increased pumping losses.
(Of course, there could instead be fundamental tuning problems
relating to fuelling and ignition coming into play.)

SAAB varies the engine's capacity to deliver power so that it works
for as much as possible in an unthrottled condition near the point
of maximum volumetric efficiency.

-- 
Real Name: Bernd Felsche
    Email: nospam.bernie at perth.DIALix.com.au
     http://www.perth.dialix.com.au/~bernie - Private HP
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