[Archived]

Roy,

I have my transmission set for automatic shifting, and I often see 2,400 RPM before it will upshift. If you are gaining speed while in 4th with the Jake on full, you may consider to brake enough so you can shift to 3rd gear to get added braking.

[Per]

DETROIT 60 SERIES ENGINE SPECS

	11.1L Detroit 60 Series	12.7L Detroit 60 Series	14.0L Detroit 60 Series
Manufacturer:	Detroit Diesel
Applications:	1987 – 1997, various on/off highway	1987 – 2007, various on/off highway	2001 – 2011, various on/off highway
Engine Type:	4 cycle turbodiesel, wet cylinder liners
Configuration:	Inline 6 cylinder
Displacement:	677 CID, 11.1 liters	778 CID, 12.7 liters	858 CID, 14.0 liters
Firing Order:	1 – 5 – 3 – 6 – 2 – 4
Engine Block:	Cast iron, wet cylinder liners, 7 main bearings
Cylinder Head:	Cast iron, overhead cam
Compression Ratio:	16.0 : 1	15.0 : 1 or 16.5 : 1	15.0 : 1 or 16.5 : 1
Cylinder Bore:	5.12 in (130 mm)	5.12 in (130 mm)	5.24 in (133 mm)
Cylinder Stroke:	5.47 in (139 mm)	6.30 in (160 mm)	6.62 in (168 mm)
Valvetrain:	Overhead camshaft, roller follower rocker arms, 4 valves per cylinder (2 intake, 2 exhaust valves per cylinder)
Injection:	Electronically controlled EUI (electronic unit injector) injection system (see DDEC section below)
Aspiration:	Turbocharged, air-to-air intercooler
Engine Dimensions (approx.):	Length – 57 in
	Width – 34 in
	Height – 50 in
Engine Weight (approx):	2,675 lbs	2,800 lbs	2,800 lbs
Rated Horsepower:	250 – 350 hp @ 1,800 RPM	380 – 455 hp @ 1,800 RPM	425 – 515 hp @ 1,800 RPM
Rated Torque:	1,100 – 1,250 lb-ft @ 1,200 RPM	1,350 – 1,550 lb-ft @ 1,200 RPM	1,550 – 1,650 lb-ft @ 1,200 RPM
Max Engine Speed:	2,100 RPM (some continuous duty applications may be governed at 1,800 RPM)

[Roy]

Note in the above spec sheet the maximum allowable RPM is 2100.

Driving in the mountains should be done as follows:

Select the target speed. When approaching or cresting the top of a downhill section be below that speed. Let’s use 55 MPH as the target speed and that speed coincides with 2100 RPM in 4th gear. Begin the downhill run at 50 MPH or lower in 4th gear. The often stated rule is to go down a hill in the same gear as you would climb the hill, but that may not always work.

Select the jake or retarder setting that will hold the speed going downhill at or below the target speed. If the supplemental braking will not hold the desired speed, apply hard steady braking to reduce speed to some speed below the target speed, such as 45 or 50 MPH. Release the brakes (to allow them to cool) and continue to allow the supplemental braking to hold the coach back. If the speed builds quickly requiring more brake application when the target speed is reached, consider a new target speed and in a lower gear. Do not exceed 2100 RPM. Do not pump the brakes because that depletes air. If using a retarder monitor the transmission temperature and use braking as necessary to keep transmission temps below 300 degrees,

Steep downhill grades require careful speed management and as a driver you are going to see warnings before you reach the downhill section of road. Up to about a 6% grade it is likely you can descend the hill using a lower gear such as 4th with the application of the jake or retarder and little or no braking. Steeper grades are going to require a lower gear or brake application as speeds increase. Supplemental is more effective at higher RPM so the target speed should be near but not exceeding the 2100 RPM limit at the selected gear.

Do not allow any drivers following you to intimidate you on the downhill run. If a car or truck is not happy with your selected speed that is their problem.

[Archived]

Per, Jon,

Good information, confirming the way I have been driving in the mountains. I always ignore the cars behind me, but will pull over in a proper pullout to let then pass, if it is big enough and has good visibility for pulling back on. I guess my question should have been what is the max engine RPM. I was not sure what it was.

I generally think of the max torque is around 1,500 RPMs but if I understand the chart correctly it is about 1,200 RPM.

Going up grades, I watch my Tach and not my speed. Generally aiming for 1,500 rpm. Am I to understand that 1,200 rpm would be a better target? More torque?

I am always in the right lane and when my speed drops below 45 mph I turn on my flashers.

Roy

[Archived]

Wouldn’t DDEC record 2400 as an over speed?

[Archived]

It will definitely show up as an overspeed. Those events will be in the DDEC memory for Detroit dealers and future buyers of the coach to see.

[Archived]

Roy, for uphill climbs drive it like you stole it. Speeds in gears, torque curves, max HP rpm, etc are all set for maximum economy and good performance under normal highway conditions. The RPMs in gears are determined by whether the transmission selector is in normal or performance mode with the normal or economy mode being the default.

But when we approach long steep hills such as 5 or 6% grades the economy mode delays downshifts to the point that we lose valuable momentum and the ability to climb the hill at a reasonable speed.

Once we lose RPMs and speeds we cannot make them up easily and have to be content with a lower speed than the bus is capable of maintaining going up the hill.

When I approach a steep long hill my first task is to select performance mode. That alone changes the shift points to cause faster downshifts and to hold gears from upshifting until higher RPMs are attained. But some hills need a fairly aggressive approach so I will downshift and increase my speed when I hit the bottom of the hill. Typically I will drop into 5th (step on the accelerator pedal to get the RPMs up as the transmission downshift) and increase my speed such as getting it up 5 or even 10 MPH. Now I am carrying some speed and momentum as I begin the climb. I prefer to use the cruise control also because that will provide a few more HP than if I am controlling speed with my foot.

Even if I can hold speed or accelerate I do not upshift because that will drop the RPM and may cause a loss of speed, but more importantly I like a higher RPM to make the fan run at higher speeds to insure better cooling.

I have no problem holding the RPM at 2100 going up a hill rather than upshifting. Usually an upshift will drop the RPM to the point where the engine is just not producing the power to hold my speed at the gear selected so I just delay upshifts until the road flattens out or I hit the peak of the hill.

[Archived]

Jon wrote: Note in the above spec sheet the maximum allowable RPM is 2100. I was not aware of that. The dash should be placarded with that limit, or the tach should have a red arc above 2100. I learn something almost everytime Jon posts.

Do not allow any drivers following you to intimidate you on the downhill run. If a car or truck is not happy with your selected speed that is their problem. I agree. I’m NEVER going to speed up to accomodate them. I will pull as far to the right as I think safe to allow someone behind to have the clearest view so they can safely pass as soon as possible.

It will definitely show up as an overspeed. Those events will be in the DDEC memory for Detroit dealers and future buyers of the coach to see. I didn’t know that. Never thought about that.

If using a retarder monitor the transmission temperature and use braking as necessary to keep transmission temps below 300 degrees. This limit isn’t new to me, but something that should be placarded on the dash and/or there should be a red arc. For many of us, Jon is referring to the gauge marked “Oil Temp” … which I think is STUPID. “Oil Temp” should be refering to ENGINE “Oil Temp” now transmission lubricant temp. I notice that Datcon (maker of the dash gauges) has a gauge labeled “Trans Temp” which should have been installed!

When I approach a steep long hill my first task is to select performance mode. More Great information.

Roy wrote: Going up grades, I watch my Tach and not my speed. Generally aiming for 1,500 rpm. Am I to understand that 1,200 rpm would be a better target? More torque? Why wouldn’t you leave let the trans/engine computers make those decisions for you? Are you not using wide open throttle on grades? or are you lifting to maintain RPM?

[Roy]

2100 RRM is the limit for under power if you force the transmission to stay in gear under power. Deceleration is a different animal. Do you really think Detroit Diesel would allow the Allison transmission to overspeed the engine under braking when the engine/transmission programming was done?

[David]

Jon, great information, I had not been comfortable running at 2,000-2,100 RPMs up grades, but I will now. I do run the performance mode, but have not been using cruise control. Thank you.

Dick, I have not been running full throttle, usually 1,500 to 1,800 RPM and down shifting to maintain those RPMs. I will be letting the computers make those decisions. I will be trying Jon’s method.

Roy

[Tim]

Dick has identified a shortcoming on earlier coaches that has been addressed on later model coaches to an extent. As a pilot he has every reason to expect that if there are upper limits which are not to be exceeded that the appropriate gauge needs to be marked.

But that is not the case on coaches that have the gauges shown below.

Perhaps the thinking of the engineers and designers is that DDEC will protect itself and if a limit is approached or exceeded the driver will get a warning light or something will shut down.

Finding accurate information about limits is extremely difficult. I knew 2100 was our engine limit for RPMs but I had to spend about 15 minutes this morning to find it in print. The same holds true for just about every value we measure with gauges. To use an example the transmission temperature gauge has no red-line but I know from reading about the transmissions with a retarder that if the oil temp reaches 300 the retarder function will be turned off or greatly reduced in effectiveness. That is not something you need to find out when descending a steep hill and need not only good brakes, but a retarder working at its maximum efficiency.

Later model coaches with the car like dash do have red-lines for upper limits, but what we really need is a section in the owner’s manual or maintenance manual for our coaches with a “limitations” section.

This is a topic we try to cover in detail in our seminars as well as providing owners with information to understand “normal”, a range on a gauge that might be marked with a green band for example, but is not on our coaches.

[Harry]

Seems to me the DDEC in my coach (with retarder) is set to show trans overheat light at 283F or therabouts…I’ve seen the light a couple times.

I try to stay under 250F trans temp on downhills. I’ve found my generally used MOST EFFICIENT retardation in 4th gear with positon 4 on retarder. Trans will overheat in 5th gear at any retarder positon over 3. Never use 5-6 except in emergency.

[TJ]

I guess the Detroit Diesel engineers are too stupid by allowing the Allison transmission engineers to overspeed the engine while under automatic control. After all, it would be a simple programming change to limit the engine speed to 2,100 RPM on an upshift.

[Archived]

Per, the programming that involves downshifts for supplemental engine braking is not a factory hard set, but can be done by dealers at the request of owners.

It has been my experience that my coach has never downshifted unless the RPM in the lower gear is at or below the 2100 RPM limit. Despite the programming which in my coach is for the retarder to only drop into the next lowest gear and only if the downshift results in a safe engine speed, I do my best to anticipate the need for a gear change and manually do the shifting so I can help make it a little smoother with application of the gas pedal.

Keep in mind however you have clearly indicated your downshifting has been programmed to 2nd gear and when your jake is engaged your transmission is doing its best to get you down to that gear as fast as possible.

I know the trend in vehicles now is to take the human out of the equation but there is a reason we are called drivers. It is our responsibility to manage our coaches and anticipate needs such as lower gears, up and downshifting, minimizing those conditions that are going to impact our engine, transmission or brakes adversely.

I am not yet ready to allow DDEC or my transmission control module to drive my coach for me.

[Per]

Jon,

Based on the way this coach has been maintained by previous owners, i can say with almost 100% certainty they did not change the way the transmission shifts.

And BTW, I am confident I am as engaged in driving our coach as any other Prevost driver!