Re: Sloth Kills Fuel Economy!

On Mar 29, 3:34 pm, Jim Yanik <jya...@xxxxxxxxx> wrote:
Nate Nagel <njna...@xxxxxxxxxxxx> wrote innews:fsm8g6026a4@xxxxxxxxxxxxxxxxx:





Garth Almgren wrote:
Around 3/29/2008 12:22 PM, Scott in SoCal wrote:

On Sat, 29 Mar 2008 12:05:22 -0800, "Daniel W. Rouse Jr."
<dwrous...@xxxxxxxxxxxxxxxxx> wrote:

So does driving over 3250 RPM in any gear when driving a fuel
efficient four-cylinder car, based on my observations of driving
several four cylinder
cars including rental cars.

Wow, that's quite a conclusion there!

What, do you suppose, accounts for this 3250 RPM barrier, and why is
it the same for every fuel-efficient 4-cylinder engine? What RPM is
best for a non-fuel-efficient 4-cylinder engine (like the one in the
1973 Chevy Vega I used to have)? What about 6-, 8-, 10-, and
12-cylinder engines?

I can tell you right now, 3250 RPMs would put my V6 Mustang at almost
88 MPH, not its most efficient speed. The Mustang gets its best
mileage at around 65 MPH and 2300 RPMs, and that's with a stone-age
carb.

3250 RPMs in the Jeep which is a somewhat modern MPI 4 banger would
put it at about 73 in 4th and 92 in overdrive, also not realistic
speeds for fuel efficiency. 60 MPH (which is the slowest I can use
overdrive) returns the highest MPG, and that's roughly 2100 RPMs.

So if you're just going to base it all on RPMs, my observations of my
vehicles place the best point at an average 2200 RPMs or so.

BSFC is a much more important number than peak torque, IMO.

Sometimes - not always, but often enough that there seems to be some
correlation - the lowest BSFC is at or near the torque peak.

nate

Uh,Rouse DID say "not go **OVER** 3250 RPMs".
(I wonder why the extra 50 RPMs? does his tach read that close? )

He didn't say "drive -at- 3250 RPMs".

(snip just for this post's purpose)

His tach is probably graduated in 250-RPM increments (4 per 1000
RPM). That is the case with mine.
.

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