RE: fifth-gear and miles per gallon

["Fry, Larry" <LEF@chem-tronics.com>]

An engine running at a given rpm can be pumping a little air or a lot,
depending on throttle position.  (If this were not true, throttle position
would be meaningless in the power output equation.)   
Granted, mixture (ratios) may not change much with throttle position, but
fuel flow must...more air requires more fuel to maintain that mixture, pound
for pound. Sound logical??

So, which situation gives the best mileage? :)

Larry  sandiego16V

-----Original Message-----
From: Marc Peterson [mailto:mpeters6@rochester.rr.com]
Sent: Wednesday, October 31, 2001 1:49 PM
To: scirocco-l@scirocco.org
Subject: Re: fifth-gear and miles per gallon


Assuming no enrichment is used...

All CIS/CIS-E engines mixed by the air flow meter flap.  If the engine is
running at a given RPM, it is pumping a fixed amount of air though it, so to
my understanding 3000 rpm is the same amout of fuel whether it is 1/2 or 3/4
throttle, the mixture doesn't change based on the throttle position.

This is different on Motronic system, obviously.  They have a throttle
position sensor.

I think the above is right.

Marc
----- Original Message -----
From: "Fry, Larry" <LEF@chem-tronics.com>
To: <scirocco-l@scirocco.org>
Sent: Wednesday, October 31, 2001 4:33 PM
Subject: fifth-gear and miles per gallon


> Hypothetical situation: you have fifth-gear ratio that gives 3800rpm at
> 80mph and it takes 1/4 throttle to maintain that steady speed.
> second hypothetical situation: you have, on the same car, on the same
> stretch of road, a fifth-gear ratio that gives 3000rpm at 80mph but it
takes
> 1/2 throttle to maintain that steady speed.
>
> question: which situation yields the best mileage?
>
> In other words, which influences miles-per-gallon more, rpm or throttle
> position?  Or is it pretty much a wash?
>
> Inquiring minds......
>
> Larry  sandiego16V
>
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