New Saab Engine Tech

[Ade + Lamb Chop]

At 10:33 18/04/00 -0500, steve ravet wrote:
>
>
>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.

I think the main advantage is as they say with a supercharger. When
cruising they switch off the charger and increase the CR so you get a nice
efficient engine when you ask for the power it kicks in the charger and
drops the CR to cope with 40psi!!

Ade

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