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Old 10-13-2019, 10:18 PM   #1
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Altitude

So drove from Albuquerque to Angle Fire. To get here we went over the Taos Canyon at 9100 ft. So this was the first time in the mountains of the West. We hit a hairpin turn and dropped to 15 mph and as I came out of the turn I pressed the accelerator and the best I could get was 2300 rpm in first gear for the last mile.

I know there is a performance loss at altitudes, but this seemed more than I would have thought. Does this sound average for a steep grade at that altitude?

2014 ISL400 engine

Thanks
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Old 10-14-2019, 09:02 AM   #2
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At 9000' the standard atmospheric pressure is only 10.1psi instead of the normal 14.7psi at sea level. Add that to a steep uphill climb (you didn't say what the grade was) and a heavily loaded coach (?) and I could believe it's normal. Those motors have some ability to compensate for higher altitudes, but unless they were specially set up for it, operating at over 9000 feet is probably well outside their operating envelope. The Air Force requires pilots to use supplemental oxygen for breathing over 10,000' and some will get mildly hypoxic below that. It took my DW and I over a month to get used to Albuquerque (5400') when we moved there from the east coast.


I assume the rig performed OK when you got out of the clouds?
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Old 10-14-2019, 09:18 AM   #3
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2300 is pretty good for a diesel. If it didn't want to upshift, I'd maybe throttle back to about 1800 and take whatever mph it'll give with the flashers on. Then, I'd try to never do that again. I give you ID33/WY22 between Victor ID and Jackson WY, and rest my case. Not what my rig was designed or is intended to do.
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Old 10-14-2019, 09:37 AM   #4
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So this post is a wake up for me.. I've been in a private message discussion about Diesel Power on hills. I had been always told that a Diesel PU Truck would be a much better choice of tow vehicle than a gas and everyone points to the Diesel for the best choice ( I know, this isn't about tow vehicles but it is pertinent)



Next, I spoke with a friend that had a fairly large MH with a Cat diesel years back and he always said he would fly up the hills of any grade.... no problem..



Then I started to think that since 2012 a big change in Diesel was introduced with the EGR, DEFF, REGEN and all the EPA stuff on the new diesels... and a lot of comments on governor... So it makes me wonder has the engine mfgrs dumbed down the diesels and cut back on the performance power because of all the emissions ...



Just a thought!
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Old 10-14-2019, 09:39 AM   #5
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Quote:
Originally Posted by XBoater View Post
So drove from Albuquerque to Angle Fire. To get here we went over the Taos Canyon at 9100 ft. So this was the first time in the mountains of the West. We hit a hairpin turn and dropped to 15 mph and as I came out of the turn I pressed the accelerator and the best I could get was 2300 rpm in first gear for the last mile.

I know there is a performance loss at altitudes, but this seemed more than I would have thought. Does this sound average for a steep grade at that altitude?

2014 ISL400 engine

Thanks
Did you shift manually to 1st gear or were you in automatic? I don't have the specs for your engine but 2300 surely exceeds the max RPM allowed under power, which I think is 2200 RPM. In auto it should shift up before exceeding the limit. In manual 1st gear it may have been protecting itself.

What is the grade of the road? I have camped at Penasco and driven to Taos a number of times but that was several years ago. That area is beautiful.
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Old 10-14-2019, 09:42 AM   #6
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I had been always told that a Diesel PU Truck would be a much better choice of tow vehicle than a gas and everyone points to the Diesel for the best choice
In two words, Diesel = Torque and Turbocharger
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Old 10-14-2019, 10:11 AM   #7
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Thanks for the info. It's food for thought that this was the motor performing as designed for the altitude. The grade was 10%+, but not signed. I tried to feather the throttle, but it was not upshifting. There is not making on the rpm gauge, I know it upshifts about 2600 when using engine/transmission braking.

Like I said this is the first time in the West and dealing with these altitudes. We came into NM on I-40, and I didn't notice a performance difference on the grades coming into Albuquerque. From there took I-25 to Santa Fe, there was one long grade that I pushed at about 50mph. We are fully loaded towing a Ram 1500.

I guess I'll see on Friday when I have to go back up and over the pass to Santa Fe. Needless to say we will dump most of the water and DW can drive to tow over the pass. That should drop about 6000lbs for the climb.

That said, if you have nerves of steel, the drive up to Angel Fire Resort is a great reward. It's a beautiful resort and area.
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Old 10-14-2019, 10:28 AM   #8
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I know it upshifts about 2600 when using engine/transmission braking.
It is allowed to go to a higher RPM using engine or exhaust braking which is a zero power operation. Under power is a whole different world and the limit (2200 RPM???) should never be exceeded. You can call Cummins to find out the limits.
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Old 10-14-2019, 07:52 PM   #9
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I have a CAPS era ISL, but believe the RPM's are relatively close... For CAPS era, vs the newer Common Rail with Variable Geometry Turbo ISL:

Braking Jake Max RPM, is 2600

Max HP/Torque, start to fade quickly after 2100-2200 RPM

I personally set a Max RPM in Braking Jake Compression, at between 2300-2400RPM. I stab the brakes and slow down as needed, to get back to say 2000RPM, and let the speed/RPM build back up to that range.

On climbing hills. I downshift to keep in the 1950-2100RPM range for hill climbing. I agree about controlling RPM's when hill climbing. I keep ours between that band of 1950-2100. And I prefer to not run at 2100RPM for too long! Will slow down as needed...

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Old 10-22-2019, 10:44 PM   #10
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Left Angel Fire Friday morning. There was only about 15 gallons of water and I let the DW drive the Ram up the mountain. The resort was about 8400 ft and the peak was just over 9200 ft. So about 800ft climb in under 2 miles.

Leaving the 6500 lbs off really made the difference. The coach made the run up the mountain with plenty of power to spare.
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