Driving habits vs performance

[Tom]

Most of this trip we've followed friends in another Monaco, a different model but the same engine and transmission. We consistently noticed that we'd have to slow down to stay behind them on hills, which I assumed was due to a difference in weight. But it turns out that, taking into account the as-weighed weights of our coaches and the specified weights of our toads, the two rigs are within 700 lbs of each other.

Questionning our friends we found out that they always leave thier coach in cruise control and never select a lower gear. Following advice we've received from other diesel drivers here, we select a lower gear when approaching a grade, irrespective of whether cruise is engaged or not. We'll also downshift again to keep the RPM up while climbing.

Am I missing something?

 

[Phil]

Questionning our friends we found out that they always leave thier coach in cruise control and never select a lower gear. Following advice we've received from other diesel drivers here, we select a lower gear when approaching a grade, irrespective of whether cruise is engaged or not. We'll also downshift again to keep the RPM up while climbing.

Am I missing something?

Tom,

You are overworking your shift select finger and your accelerator pushing foot.  Let the cruise control do the work and just enjoy the ride.  Of course, if you think that you can do a better job than the engine and transmission computer, by all means push the button all you like.  ;D 

BTW, the cruise control upper and lower droop are adjustable.  Cummins claims you can increase fuel economy by increasing the droop but I have mine set at zero.  If the mode switch is on, it does increase the droop but I usually turn it off when driving in hilly country.

Phil

 

[Tom]

You are overworking your shift select finger and your accelerator pushing foot.

I'll let the driver know that Phil  ;D . As I said, previous advice here was to select a lower gear when approaching a grade, even if in cruise control. There's no doubt that the engine labors some when the transmission waits too long to shift. RPMs drop and the engine doesn't fully recover. Downshifting makes a huge difference, even with cruise on and we blow by everything in front of us.

BTW, the cruise control upper and lower droop are adjustable.

I have no idea what droop is, so I guess I should get my Cummins manual out 

 

[Tom]

Phil

From an official Allison document entitled "Driving tips" included with my Allison onwers manual:

Situation: Mountainous Driving (Up & Down Terrain)

Technique: Manually preselect a lower gear in order to maintain engine speed within a range of 500 RPM of engine governed speed. Road speed may decrease but power (torque) will remain at peak output while ascending a grade ......

Seems like my driver is doing exactly what Allison recommends  ;D

 

[Phil]

Downshifting makes a huge difference, even with cruise on and we blow by everything in front of us.

I have no idea what droop is, so I guess I should get my Cummins manual out 

Tom,

I recommend that you download the Cummins Power Spec program.

http://www.powerspec.cummins.com/site/home/

It will explain all the optional features that you can program into the Cummins/Allison computers.

Blowing by everyone in front of you is a little hard on fuel economy.    The computer can be programmed for maximum power, maximum economy or somewhere inbetween.

Phil

 

[Tom]

Thanks Phil. It took a little while to download the 8Mb file on my 40K connection  but I have it installed and started playing with it. Need to spend more time with it, but it looks like a neat tool.

Thanks again.

 

[Gary RV_Wizard]

It's an automatic transmission, Tom. It will shift if it needs to.  Since you can look ahead and see what the upcoming terrain looks like, you can anticipate a bit and choose a lower gear a bit sooner than the tranny will, but it isn't necessary unless the transmission is "seeking" or "hunting", i.e. frequently up/down shifting tto find the appropriate gear.

I think the reason you had to slow down when following your friends has more to do with Chris's right foot than engine or tranny. 

 

[Ned]

If the transmission is hunting, as it will do in rolling terrain, you can use the mode switch to lower the shift points 200rpm.  This will keep the Allison in 6th gear (or 5th, etc.) longer than in normal mode.

 

[Tom]

It's an automatic transmission, Tom.

I didn't know that  ???

has more to do with Chris's right foot than engine or tranny.

Long before Chris started to use this procedure, I was doing it regularly after reading advice from a few long-time diesel owners here. There is no doubt that the auto downshift occurs late and RPMs drop too low, causing speed to drop and the transmission downshifts again. Pre-selecting a lower gear all but avoids that. Of course, the transmission shifts when it's safe to, but it shifts sooner than it would if I didn't pre-select the gear.

It appears that the system can be re-programmed using the Cummins software tool that Phil referred me to, but I haven't had time to fully explore/understand it. Plan to do that before making any software changes to the engine or transmission  ;D

 

[Tom]

Thanks for the tip Ned. We don't appear to have a hunting problem, but will keep that in mind if we see it happening.

 

[Jeff]

Tom:

Cat's advice for fuel economy is to leave mode switch engaged unless temperatures start climbing OR more torque is desired.

I assume the same advice applies to Cummins.

 

[Tom]

Maybe so Jeff. Guess I should read the manual  ;D

 

[Phil]

Guess I should read the manual  ;D

Never admit that in public, Tom. 

 

[Tom]

LOL Phil, it's a known fact I don't read manuals.

 

[John From Detroit]

If the transmission is hunting, as it will do in rolling terrain, you can use the mode switch to lower the shift points 200rpm.  This will keep the Allison in 6th gear (or 5th, etc.) longer than in normal mode.

Speaking of Allison Transmissions.... On my gas powered rig (not diseal) there is a switch called "Grade Brake" or "Grade Control" (not sure which and can't check just now) which I'm told changes the transmission shift points or rations so as to increase engine braking when going DOWN hill.

Can you explain this to me.. Seat of pants does not notice much effect when using it

 

[BernieD]

Most of this trip we've followed friends in another Monaco, a different model but the same engine and transmission. We consistently noticed that we'd have to slow down to stay behind them on hills, which I assumed was due to a difference in weight. But it turns out that, taking into account the as-weighed weights of our coaches and the specified weights of our toads, the two rigs are within 700 lbs of each other.

Questionning our friends we found out that they always leave thier coach in cruise control and never select a lower gear. Following advice we've received from other diesel drivers here, we select a lower gear when approaching a grade, irrespective of whether cruise is engaged or not. We'll also downshift again to keep the RPM up while climbing.

Am I missing something?

Tom

I don't think you are missing anything. There are two concepts of climbing a mountain; being the first up to the top and using the least amount of fuel. I previously used the cruise control with a manual downshift to prevent gear seeking. With the TS and Cummins ISL engine, I just leave it in cruise, and even in economy mode, and let Allison pick the gear. Cummins now recommends that process. You can't lug the engine because the transmission will downshift before the RPMs drop below the peak torque output. This will not be as fast up the hill as manually downshifting but will be more economical and will save fuel.

 

[DougJ]

Would this advice, Bernie,

I just leave it in cruise, and even in economy mode, and let Allison pick the gear. Cummins now recommends that process. You can't lug the engine because the transmission will downshift before the RPMs drop below the peak torque output.

also apply to a gasoline powered Class A--F460 engine with the E40D transmission?

I tend to take mine out of overdrive in undulating territory even though I may leave it in cruise because I note the vacuum gauge going down into the yellow range, even well down into the red range.

Ciao,

Doug

 

[Tom]

There are two concepts of climbing a mountain; being the first up to the top and using the least amount of fuel.

LOL concisely said Bernie.

 

[Smoky]

Tom:

Count me firmly in the school of "leave it in cruise".? "Blowing by" someone else on a hill climb is not within my budget plan.? Likely you have made the right choice for your technique (or your captain's) if speed is the main concern.? I think Bernie hit this issue right on target.? Speed versus economy.? Being retired and fulltiming, I mostly cruise at 55 mph and watch almost everyone blow right by me.? Until I pass them at the truck stop.? ?

 

[BernieD]

Would this advice, Bernie,

I just leave it in cruise, and even in economy mode, and let Allison pick the gear. Cummins now recommends that process. You can't lug the engine because the transmission will downshift before the RPMs drop below the peak torque output.

also apply to a gasoline powered Class A--F460 engine with the E40D transmission?

I tend to take mine out of overdrive in undulating territory even though I may leave it in cruise because I note the vacuum gauge going down into the yellow range, even well down into the red range.

Doug

I would think not. Gas engines build torque and HP as the RPMs climb, diesel engines usually have peak torque at the low end. To get and maintain adequate HP, you would probably have to keep the RPMs up on the gasser.