what speed gives you the best gas Mileage

MaXJohnson said:
the former national speed limit of 55 MPH was set by an act of Congress, specifically to reduce fuel consumption and reduce traffic fatalities.

...and it failed miserably on both fronts...

Note that traffic fatalities PER MILES DRIVEN have pretty well kept on a downward trend since the 60's... except for the small spike that corresponds with 80mph SUV drivers on cell phones....

What should the speed limit be? Tough call. But I can't support ANYTHING that lets a 32-ton rig drive as fast as a sports car...

Den
 
Vertisce said:
Say what? Get a clue...when your engine shifts down your RPMs go UP and vice versa. Linear progression has nothing to do with RPMs vs MPH. I didnt even mention that wind resistance and other elements can factor in. He is the one that came and told me that MY numbers were wrong when MY numbers came straight from my meters.

Yeahbut....

A manual tranny will be "locked in gear" at any speed... unless the clutch is worn the point of needing replacement SOON. (Aka, holding speed on the highway is a pretty light-duty part of it's job). If you're trying to compare mileage at different speeds, you won't be shifting....

Likewise, once an automatic-tranny XJ (stock) hits about 45mph at light throttle, the torque converter will lock up... and unless you jump on the gas pretty hard, it's gonna stay locked up.

Hence... manual or auto... at highways speeds and reasonable throttle openings, the engine speed and road speed will vary in a directly proportional way.

Den
 
May be true but what happens when you hit a hill? Or a gust of wind? Resistance is applied and the engine RPM's ramp up in order to keep the speed...
 
Vertisce said:
May be true but what happens when you hit a hill? Or a gust of wind? Resistance is applied and the engine RPM's ramp up in order to keep the speed...
Only if the torque converter unlocks or the transmission downshifts. Other wise, you just mash the peddle and the engine burns more fuel to maintain the same speed AND RPM.
 
The Best Mpg Ive Gotten Was On Way Home From School I Had A Kickass Tailwind I Was Doing 80-85 And Getting 28 Mpg..

2001 Limited, 4.0 4x4, Banks Header, Custom Flowmaster Exhaust, K/n Intake..
 
One day when I was driving the wife's WJ, I started playing with the little computer. The instant gas mileage was showing the best fuel economy at around 60mph. I also tried windows up A/C on windows down and A/C off with inconclusive results.
Too many variables to be certain about anything.
 
old_man said:
To maximize mileage, we used to use a vacuum gauge. You would vary the throttle position and the gear to keep as high a vacuum as possible.
damn you are an old man ohh wait i remember those vacuum gauges too...damn guess i am too
 
langer1 said:
Always daft behind a 18 wheeler when you can.

Now theres some solid advice??

Epitaph=
"I died that day with rock chips in my windshield, but I got 22 MPG (crumple zone my a$$)".;)
 
Vertisce said:
May be true but what happens when you hit a hill? Or a gust of wind? Resistance is applied and the engine RPM's ramp up in order to keep the speed...
And just how preytel, does the engine speed increase without downshifting or the vehicle gaining speed? clue me in, if you would be so kind. Id love to hear this one!!! Have you dyno'd your rig lately to check for clutch slippage? Just seems to defy all laws of physics..(burning tread fighting that nasty wind perhaps?)...someones been putting bogus numbers on my slide rule again........ damnit, Ill have to hide the white out
 
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majic_tech said:
And just how preytel, does the engine speed increase without downshifting or the vehicle gaining speed? clue me in, if you would be so kind. Id love to hear this one!!! Have you dyno'd your rig lately to check for clutch slippage? Just seems to defy all laws of physics..(burning tread fighting that nasty wind perhaps?)...someones been putting bogus numbers on my slide rule again........ damnit, Ill have to hide the white out

The torque converter unlocks.
Ah,ha, gotcha!;)

EDIT: darn, eagle beat me to that one.
 
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Ray H said:
The torque converter unlocks.
Ah,ha, gotcha!;)

EDIT: darn, eagle beat me to that one.
actually you got yourself he didnt even mention that at all go back and read dude it was in referrance to both as I read it (manual and automatics)
 
Youre right dude. I got myself, jokes on me.
 
Old???? I'm old enough to be your old man.
 
max economy occurs at 30mph +/- 5 mph
If you disagree, I will fight you... with math.

however, you see a very small penalty to efficiency as you speed up to as much as 50mph.

Now, my engine runs rich as **** so If I'm not into the throttle then unburnt gas is puffing out the exhaust anyway. I do better the faster I go because I spend less time throwing gas away.
 
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