Just ran 1025 miles getting to St Augustine Fl and ran the coach in economy mode like Brett recommended and got 8.9 mpg vs the 7.5 in performance mode. Ran steady 65 mph. Couldn't be more pleased with results.wasnt towing anything but still pleased with the number. Feel like a dummy for not knowing more about the 6 speed but haven't had it a year and drove a 4 speed for the 10 years prior.
Dub,
One other thing is, you can have Allison change the ECM to default to economy mode (or you could in the past). You will have to push the button to make it go back to performance mode.
Mike
I never could figure out if there was any difference. Please explain the benefits of Eco mode and how to tell which mode your coach defaults to.
And what is the maximum rpm for the M11 engine?
folivier,
Here is a link to what Brett has wrote up.
technical:transmission:econ [ForeForums Foretravel Motorcoach Wiki] (http://wiki.foreforums.com/doku.php?id=technical:transmission:econ)
This is better than me trying to explain.
Mike
Just ran 1750 miles and used the mode button. Haven't figured the mileage yet, need to fill the tank to get accurate number.
Larry
Short answer to "difference in MPG" is THERE IS NO SIMPLE ANSWER.
On totally flat ground (say, I 10 across Louisiana) it will make zero difference, as the transmission will stay in 6th gear all the way across.
Move west on I 10 to the hill country of Texas. Economy mode, you will stay in 6th on most of the grades. Power mode, you will downshift to 5th on most of the grades. Significant difference in MPG.
Here is what Cummins says about M11. 400 and 450 HP
1,450 pound force-feet (1,966 N⋅m) @ 1200 rpm, 400 horsepower (298 kW; 406 PS) (246 kW) electronically governed at 2,100 rpm
1,450 pound force-feet (1,966 N⋅m) @ 1200 rpm, 450 horsepower (336 kW; 456 PS) (246 kW) electronically governed at 2,100 rpm
Roger I didn't realize that we had that much torque. Was thinking it was in the 1100 pd range. No wonder I can just chug on past the big rigs, let alone the SOB's
Larry
I usually use economy mode (mode light on) except in real mountain driving. It is my impression that when the transmission is in the economy mode it will sometimes "dither" between gears going up a hill. That is it will downshift to 5th, for example, then a minute or so later upshift to 6th and repeat. This is when I downshift manually to 5th. But if I have mode off, this does not happen, at least as much. The transmission downshifts and stays there until we reach the top of the hill. Now the situation may be different in "rolling hills," but that is not what I'm talking about. I'm talking about real hills with grades of 5-6%.
Long term user posted here .4mpg increase using the mode. Just shortshifts the motor.
I agree it feels like 1100 torque.
George your shifting results reported seem backward.
I wonder if someone set your trans to mode as the default?
So what would be the preferred rpm on a steep climb?
I find that if I keep the engine at about 2000 rpm then the temp. stays pretty constant, but if I'm at 1500-1800 rpm the temp. will start to rise. I usually try to keep it at 2000 rpm.
Doesn't make sense to my feeble mind that the max. torque is rated at 1200 rpm. and the engine seems happier (based on temperatures) at 2000 rpm. Am I making more torque? or is the cooling more efficient at that higher rpm?
Thanks for the info on the mode.
Motor has weak torque. So the hp can go slightly faster up grades.
If we could raise the torque we could sixth gear all the interstate grades....
Using the gear that results in the lowest throttle opening will usually result in the best fuel use. There is a fixed amount of torque required to climb a grade. Divide that torque value by number of piston strokes.. Use 6 gear, lower number of strokes, vs 5th gear. That is why the bus feels happier in 5th, within reason of course. More revs= more water and air flow through the engine.
For those with the data system, watch the #s of fuel per min value and choose best gear from that.
I think it's funny to hear you guys with 1,450 lb-ft of torque crying about your "weak" engines, when I get along fine with a measly 820 lb-ft. 8)
In performance mode mine would down shift every time I pressed resume on cruise control even if at the speed I had it set on. Mine would downshift at times where there was absolutely no need. Stopped that nonsense now and get decent mpg. I figured my mileage the old way, dividing gallons into miles.Used 60 gallons to travel 535 miles.. last fall it figured 7.5 mpg on the same route.
We feel that to get higher MPG, it comes from loading engine more before it changes gears. Lower gear ratios use more fuel, but also lower engine loads. We use power mode 100% of the time as we figure it helps our engine. It takes power to move our 30,000 around.
If you want an excellent insight into RPM for best MPG, LISTEN TO THE 18 WHEELERS. All (certainly all the privately owned ones who pay for their own fuel) climb those grades (yes, with more than twice our weights) JUST ABOVE PEAK TORQUE RPM. THAT IS THE BEST MPG.
Now, if coolant temperature is rising, MPG takes a distant back seat to temperature. Higher RPM, slightly less than WOT is much better for cooling. It is also better for those who are frustrated by looking a few MPH on those grades.
As to the mode which the trans defaults to with the key on, I believe it depended upon the original purchaser's preferences. Ours starts out in economy mode and the label above the mode switch says "Power". When the red light above the mode switch is on, we are in power mode and it is easy to tell based on the shift points. Unless running on the flats, I usually put it power mode, otherwise the cruise speed sags too much before downshifting and then I have to apply more throttle to reacquire the desired cruise speed. I don't see how that could help the MPG any but I am more concerned with the driving experience than the MPG anyway. The temperatures don't seem to vary much either way on our coach as the coolant temps seldom rise above the 190º's let alone over 200º. More typically, the temperatures run between 182º and 187º.
Don
In what year did Allison introduce the 6 speed with the "economy" - "power" -(normal )? Options? Don't recall reading about it in my manual.
All Allison 6 speeds have power/economy mode. Certainly true on our 1993 U240.
Look at your Allison shift pad-- upper right corner for the button and light.
FT.. do you not have a "mode" button on your Allison keypad ?
Yep
Mode is there
It would be EXTREMELY RARE for the Allison ECU to be programmed with economy mode as the default (selected each time the coach is started). Could a previous owner have had an Allison dealer reprogram it-- sure.
So, easy test to verify:
On a clear stretch of road, transmission in the mode that came up when you started the engine (i.e. the default mode)-- correct, that means you have NOT pushed the mode button: Accelerate WOT from a stop to 50 mph or so noting highest RPM in each gear.
Next stop sign with clear stretch of road, push mode and repeat. There WILL be a difference in RPM before upshifts.
Your good then, mode on for the rolling hills.
We just retuned from the Texas hill country and I went through the 5th to 6th thing. Wish this thread would have started before, I think I already new about the mode thing but spaced it.
This morning I left Watson Lake, Yukon and drove to Carcross with the mode ON in economy. Big difference in the mountains here, no gear hunting going uphill. Ambient temp was in the 40's so didn't notice any difference in engine temps. Too soon to tell if mpg's was better. I'll plan to use eco mode more often.
Thanks for the tips and thanks Brett for writing that article!
As a former trucker. You are correct. Torque gets work done, HP maintains the work. The hard thing for all the indy 500 drivers in buses is that to climb a hill at max efficiency, You need to be at max torque. Which means slowing/shifting down so torque multiplication (lower gear) lets the bus maintain speed at less than full throttle.
When I owned my Kenworth W900 with a 15 liter Cat engine rated at 500HP-1950LbFt torque, 13 speed tranny. Pulling two FedEx trailers 60,000lbs across Northern Wyoming at 75MPH. I would get 5-5.5 MPG by shifting to stay at max torque.
Yep,
sure missed that memo..............learn something new about these machines just about every time I log on to this forum, a truly great resource. ^.^d
Torque is what gets us up the hill. Horse Power is what determines how fast we get up the hill.