New Saab Engine Tech

[steve ravet]

Doug Dayson wrote:

>  1. Reducing the enaine dispIacement- size does matter
> 
>  A conventional four-stroke gasoline engine is most efficient (maximizing the
>  energy in the fuel) when it is running at a high load. A small engine must
>  work harder and run closer to full load if it is to perform the same work as
>  a bigger engine, which utilizes only part of its maximum capacity. The small
>  engine often extracts more energy from every drop of fuel.
> 
>  One reason for this is because the pumping losses are lower in a small
>  engine. Pumping losses arise when the engine is running at low load and when
>  its fuel consumption is relatively low. In order to maintain the ideal
>  air-to-fuel ratio (14.7:1), the air supply must be restricted by reducing the
>  opening of the butterfly valve in the air intake.

I've certainly heard this a bazillion times.  Can someone explain to me
why I get the same mileage now in my S-10 Blazer with a 5.7L TBI engine
as I used to get with the stock 2.8L TBI engine?  Granted the 2.8 was an
'86 calibration and the 5.7 is a '91 calibration.  And I have to admit
that highway mileage is a little worse, but city mileage is the same. 
The 2.8 was a wimp in that truck, which weighs in at over 4000 lbs. 
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.

anyone?

--steve


-- 
Steve Ravet
steve.ravet at arm.com
ARM,Inc.
www.arm.com
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