Community Forums

Mr_D · 04-30-2015, 11:41 PM

Quote:

Originally Posted by dons2346

". I can pull most of the mountain grades in 6th gear and the engine never shifts down. I did this on a trip from Arkansas to California on I40 Through some pretty steep mountains. On the way back I traveled through North California and traveled accross the mountains around Lake tahoe. My engine had more than enough power to pull in 6th gear."

Wow! That must be some kind of motor and transmission setup to do mountains in 6th gear

I'm not sure what he weighs but our Magna weighs right at 50,000#'s the way it's loaded (GVWR is 54,000 GCVWR is 64,000#'s) and we were pulling a 4,500# Honda Odyssey with a 650 ISX. Even with that it did downshift a few times from 6th to 5th but I found that using the economy mode in the Allison on cruise worked the best.

SteveLevin · 05-01-2015, 01:00 AM

I have the smaller ISC, so some of my experiences may not mate up, but with my coach, when I climb, I climb flat out throttle if at all possible. That makes the transmission downshift well before the engine begins to turn slow enough for heat to be an issue. If I have to climb at partial throttle, then I may downshift manually if needed, but with only 300hp/950tq, my coach just isn't that fast (it'll pull a 6% grade at 50mph which is 2000rpm (2200 redline) in 4th, and an 8% grade at 44mph at 1750rpm, which is plenty to keep the water moving well).

One thing to remember when manually downshifting is that while the Allison transmission won't shift into a lower gear until you are going slow enough to not cause an over-rev, it will not protect you from over-revving the engine in the gear you are in (in other words, if you shift down to 4th, then things flatten out and you start accelerating and forget to go back to "D", you CAN over-rev the engine).

Steve

twinboat · 05-01-2015, 05:59 AM

Steve,

You CAN NOT over-rev a diesel engine on flat ground, just as you cannot over-rev one in neutral. They ALL have a governor, to limit, high RPM.

The only way to over-rev a diesel, is to run, down hill, in a lower gear, but, to my understanding, Allison trans. will up-shift to prevent that.

Coma · 05-02-2015, 07:20 AM

First, you have a beautiful trip planned, enjoy. You are right to be concerned. Density altitude will affect your cooling system adversely. The Cummins is rated at 100% continuous power up to 10k feet. I seriously doubt your cooling system will allow it, however. Keep your RPM at 2k and your boost at 3-5 psi off of max. Select your gears manually to achieve that. With a two stage Jake descents are likely to be handled in the same gear as ascent. If you'd had an exhaust brake instead then I would suggest a gear lower for descent.

loisjop · 05-02-2015, 07:50 AM

Well if you're not throughly confused by not I'd be surprised. Your motorhome has an AUTOmatic transmission and if the manufacture set it up right you won't have a problem with temps. You will not go over Wolf Creek pass or Lizard head pass or anything that has the word pass attached in 6th gear. For sure you need to watch all instrumentation, but you'll find what works for you.
Lastly enjoy the trip and let the motorhome take care of itself with a little oversight from you.

Gordon Dewald · 05-02-2015, 10:28 AM

IMO if you are climbing it is better to leave the transmission in normal mode rather than econo. Econo will let the engine pull down so when it shifts it hits the best power curve for the engine. Normal mode will shift earlier and thus will not pull the engine down as much.

dons2346 · 05-03-2015, 10:14 PM

The best way to climb a hill is to get the RPM into the max torque curve and to heck with the speed. You will also get the best MPG which is more important to me than speed