Diesels and The Mountains

[B Dubya]

Well if we DO buy a newer MH, it would be a 330, 340, or 350, as those are the type Motorhomes I expect would be in our anticipated budget. If I can do it in my gasser, I suppose it would only be better in a DP. Notice I didn't say 'assume'?

[B Dubya]

I5 from here to Oregon has 12 or 14 6% grades, up and down. I know every one of them from memory. I am one with them. Hummmmmmmmmmmmmmm..........

[Gordon Dewald]

Somewhere I read in a thread that the ratio of one horsepower per hundred pounds would give reasonable performance. We are running 118 lbs per hp and find the performance more than adequate.

Diesel engines are ran on a dyno meter and the torque is measured. HP is determined by multiplying the torque X rpm / 5252.

[bluepill]

Very happy with the Cummins 6.7 L ISB 350/700 in our 37 footer. Spent about a year going around the USA towing a 5K Lb. SUV and had no problems.





The longest grade we pulled was Cajon Pass from San Bernardino up I-215/I-15. It took about 25 minutes running full throttle at about 45 MPH. Engine and transmission temps went to about 210 degrees and stayed there. I just kept it in the right hand lane and let traffic pass me. Other passes in the Rockies were also no problem.

The bonus is that we averaged 10 MPG over 30K miles. I doubt we would have seen that with an ISC or ISL.

[Mr_D]

Originally Posted by montyhp

6% grades are fairly rare and usually marked with signs.

Not out here on the west coast.

[spinn]

Don't be worried about doing 45 up a steep grade. Worry about catching up to the 18 wheeler in front of you doing 20 and you can't get around! Loose your momentum and you will be wishing that 6 speed tranny had 5 more gears!

[Ron_H]

Originally Posted by montyhp

6% grades are fairly rare and usually marked with signs. Pick a route that you think is really mountainous and plot it in google earth. Then view the elevation profile and run your mouse along the route. It will show the percent grade. We are starting in Junction texas next weekend and going to ruidoso. I thought it was a huge climb, but grades over 1% are fairly rare.

It all depends on where you are. Come on out to the west coast and I'll take you on a couple of 13% grades. 6% are very common out here.

[S Bradley]

Try the Fraser Canyon is located in British Columbia, it is one of the longest grades I have seen. I avoid it going up or down.

[BillJinOR]

The 330 35ft Winnie journey we had did just fine . As already written out here in the "west" there are plenty of 6 % grades both short (1-2 miles) and much longer. Towing on several 6 mile plus grades we were down to 45 . But it was a relaxed , quiet drive with the engine way in the back running at a little over 2000 , not winding out loudly at considerably more. The engine brake meant hardly touching the brakes on the other side ! The heavier frame, larger brakes , air suspension ,better ride , increased storage capacity, real tile floors etc etc are all in there making the uphill performance perhaps similar, yet the diesel is doing a bit more for the comfort level. While pulling a bit more stuff up that hill.

[Steve Ownby]

Originally Posted by B Dubya

Just looked at a Forza 34t. Really nice. So I looked at the reviews. It has a 340 HP Cummins, and produces 700 ftlb torque. The review was on a 38, but said it would only do about 45 mph climbing a 6 grade, and that was with no toad or trailer. I really thought these things would pull faster (reminds me of a couple videos I watched here recently) when climbing. So what do you have to do? A 400? 450? I'm really blown away by this. Here's the link if anyone cares...

Molto Forza!

That may or may not be a true measure of the performance of that motorhome. The trick in a diesel is to keep the RPMs up close to the hp peak when climbing a significant grade. Particularly with the small ISB, if you let your RPMs fall off too much, you just don't have the available power to get them back.

[mel s]

Originally Posted by B Dubya

Just looked at a Forza 34t. Really nice. So I looked at the reviews. It has a 340 HP Cummins, and produces 700 ftlb torque. The review was on a 38, but said it would only do about 45 mph climbing a 6 grade, and that was with no toad or trailer. I really thought these things would pull faster (reminds me of a couple videos I watched here recently) when climbing. So what do you have to do? A 400? 450? I'm really blown away by this. Here's the link if anyone cares...
Molto Forza!

B Dubya
The 250HP 3126 Cat diesel engine in my 35' 24,000 lb coach has never had a problem towing my 3,000 lb Saturn up any mountain grade as fast, (or faster), than a lot of 18 wheelers.
Mel
'96 Safari, 148k miles

[Dennis_K]

FYI, The Forza has a 2100 or 2500 series Allison transmission. If so it is a normal practice to display the 340hp / 700lbft rating. If you look at that transmission spec it states:

2100 MH Wide Ratio 340hp (max), 700lbft (max), 26,000lb (max GVW), 30,000 (max GCW)
2500 MH Wide Ratio 340hp (max), 700lbft (max), 33,000lb (max GVW/GCW)

The notes are:
SEM and torque limiting are required to obtain this rating.
SEM = engine controls with Shift Energy Management.

So basically the engine has a torque limiting system because of the transmission. If it has a 3000 series transmission the rating is 450hp / 1250lbft and no CVW/GCW limit. That is why other units show more torque with the same HP. For instance my 350hp engine has 1150lbft of torque with a 3000 series trans.

[Steve Ownby]

Originally Posted by Dennis_K

FYI, The Forza has a 2100 or 2500 series Allison transmission. If so it is a normal practice to display the 340hp / 700lbft rating. If you look at that transmission spec it states:



2100 MH Wide Ratio 340hp (max), 700lbft (max), 26,000lb (max GVW), 30,000 (max GCW)

2500 MH Wide Ratio 340hp (max), 700lbft (max), 33,000lb (max GVW/GCW)



The notes are:

SEM and torque limiting are required to obtain this rating.

SEM = engine controls with Shift Energy Management.



So basically the engine has a torque limiting system because of the transmission. If it has a 3000 series transmission the rating is 450hp / 1250lbft and no CVW/GCW limit. That is why other units show more torque with the same HP. For instance my 350hp engine has 1150lbft of torque with a 3000 series trans.

I agree completely that the Cummins ECM sets the torque/hp max in many cases and maybe even in the case that the OP is considering. I'm guessing however, the the engine in question for the OP is a Cummins ISB. The ISB can't be "turned up" by the ECM to produce 450 Hp or 1250 ft/lbs of torque. Your 350 hp engine is most likely a Cummins ISC. The 450/1250 you reference is a 2010 or later Cummins ISL. I doubt you will find a Allison 2100-2500 transmission mated to any Cummins bigger than the ISB.

[DMTTRANSPORT]

The idea of the Diesel Engine is not to go fast but to get the weight efficiently down the road and up the hills...