Interesting find.

My gf's house is a 10-11 mile trip and the speed limit varies from 30-35mph. Whole trip is more or less 40mph when driven to stay with traffic.

In OD with converter locked, at 38-40 mph and speed steady I need 1.7-1.9ms inj. pw's tp hold speed.

In third with the converter locked I only need 1.3-1.6ms inj. pw's.

More or less comparing back to on flat roads. I saw a drop from 1.8 to 1.4 ms pw's going from OD to third leaving the converter locked up.

Might be something to consider for all the folks here who have f-bodies w/ the good rear gears. U will hit OD at 30-33mph and lock up at 38 if your using anywhere near stock settings. That equates to basicaly a 20% decrease in pulsewidths whch directly correlates to how much you put in at the pump.

Something I found, hoep it helps someone.

later
Jeremy

 

Good info! I need to check out the same thing using my T-5, chances are the 5th gear will do the same thing at 40MPH.....

 

Fuel flow = effective duty cycle * flowrate = f(PW & RPM)*flowrate.

RPM is still important.

Lower RPM with higher PWs can still be more efficient than higher RPMs with lower PW. From your post, it sounds like you are only considering PW and MPH.

 

He beat me to it. That's exactly what I was going to say.
My buddy did a test where he drove for a week to work in drive and one leaving it in overdrive. He thought he'd gain mileage in drive but he didn't. It was noticably better with OD and that's a big boat of a car, 96 imp SS with stock rear gears.
The "sweet" spot of an engines RPM range is almost never the spot you want to be cruising in. Any motor that is worth talking about displaces a lot of air as engine RPM increase. This added windage (pumping losses) and friction increase the BSFC. In a smaller more efficient 4 cylinder the lowest BSFC point is closer to it's peak torque but with large v8's it's lower.
From tuning a lot for mileage I found running the least amount of timing needed to keep the lowest MAP was best and running lean helped a bunch. Now running lean might not help everybody but I found it worth it and the oil temps didn't go up much, infact they seemed to go down when I took out some timing. I use OD religiously because of my 3.73's and the fact that my TC is too loose for this engine. All in all one of the best things you can do for an auto car is get an efficient torque converter. They'll save your city mileage from plumiting into single digits.
Don't forget the proper rake on the vehicle (no front ends up in the air), lower the car as much as possible to decrease the frontal surface area, wash the car , pump up the tires while hot, offer to drive when there is some gas money in the contract , and lastly, monitor the pulsewidth to RPM to figure out how much fuel you're really consuming.
Here's an easy way to compare; RPM x pulse width. So if I'm cruising at 2200rpm with 1.9 msec, that's 4180 msec/minute. Now 2800rpm with 1.6msec is 4480 msec/min which is obviously more fuel. It's next to impossible to derive the EXACT mileage from pulse width but you can get close if you do some math based on the fact that injectors don't flow much while opening... but that stuff is highly dependent on injector design.

 

Interesting,

I didnt think of it that way, its 1200rpm converter locked in OD at 38-40 mph and 1800rpm in D w/ converter locked at 38-40mph.

Doing the math as you say it comes out to 2100pw msec in OD vs. 2610 in D......

Makes perfect sense, now I hate you guys :-)

Actually on washing your car, they have done tests and a clean waxed car can get you 1/4mpg vs. a dirty bucket of rust

I cant win :-)

Back to the drawing boards lol

later
Jeremy