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Old 06-16-2016, 06:59 PM   #1
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Diesels and The Mountains

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!
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Old 06-16-2016, 07:12 PM   #2
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Consider the weight of your vehicle then the fuel, water, food, clothes and all the "junk" we carry and 45 MPH is pretty good for a 340. If it had a gas engine, I doubt you'd be going that fast without overheating the engine. I have a 400 ISL in my coach and I'm perfectly happy. I climbed I-70 west to east all the way to the tunnels at 11,158 ft. at about 50 MPH pulling a GMC Envoy. Going up was fine but going down towards Denver was a thrill a minute NOT !!!
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Old 06-16-2016, 07:16 PM   #3
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I wouldn't be spooked about a coach that slows to 45mph on a long grade...

Unless you're one of those that has the need to get to the top of the hill first, I doubt you'll find a 340hp equipped 35 footer lacking when compared to other traffic you're running with.

Our 275hp rig does fairly well holding it's own with other trucks even when pulling a toad (we don't go anywhere without a toad!). No, we aren't the fastest, but not the slowest either. In short, we have no trouble blending in with traffic going up any incline we've tried to date.
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Old 06-16-2016, 08:02 PM   #4
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I don't have a problem climbing those mountains with our Cat C7 330 hp 860 FT Lbs.Very pleased with that engine, except for the fuel mileage.
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Old 06-16-2016, 08:08 PM   #5
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The going up ain't nothing , the coming down is were you need a larger engine !!
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Old 06-16-2016, 08:14 PM   #6
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We have a '15 Winnie 34T and have taken it up and down the Rockies a number of times. We pull a Lincoln MKZ and have no problems either going up or down I-70 or any of the other passes here in Colorado.
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Old 06-16-2016, 08:49 PM   #7
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I get down to 45 MPH going up long 6 and 7 percent grades with the 330 HP Cat. This seems to be the speed with and without pulling the Jeep or Boat. Sometimes I have to pass big rigs, sometimes they pass me.

Many years ago my parents had a 1989 37 foot Fleetwood Limited with a 460 Ford. It would get down to 25 MPH in similar conditions at half the fuel mileage I now get with my Coach now.

In both cases, I was/am happy to be away from work and on my way to play. It is certainly a step up from the tent camping we used used to do (afford). It may take me a slight bit longer than some with lots more hp, but so what. I eventually get there.
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Old 06-16-2016, 08:57 PM   #8
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I don't want to mislead anyone. My gasser goes 44-45MPH up a 6% all day long, and the ambient temperature has no effect on my cooling (wish I hadn't said that B4 my August trip). I don't have a problem with that as I'm in no hurry anymore. I don't like the braking going down the same grade, but I've been doing it for dears, so it is what it is. I was just of the understanding that a 340 or 350 CAT would pull these hills a lot better (faster). I guess the 400 is where the rubber really meets the road. Me 'n the Misses are seriously talking about getting something newer/nicer, even though the Vacationer is really fine for what we do. Ehhh, it's just conversation. We have plenty of time to figure which direction we want to go. Thanx for the responses.


PS. I can't keep her from going to RV shows. They're the REAL enemy!!!
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Old 06-16-2016, 09:11 PM   #9
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It's the torque, not the HP. My F250 has 400HP, but only 800 FP. My ISM has only 450 HP, but 1550 FP. The ISB, although a very powerful engine in a RAM truck, is a very small engine in a 30K+ MH.
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Old 06-16-2016, 09:16 PM   #10
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Scott, I understand the whole torque thing. Just don't understand how a 350 produces 700 or so in the torque range, then a 400 or 450 gets basically double that. I guess technology. I don't know enuff 'bout them to get any deeper than that!
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Old 06-16-2016, 09:33 PM   #11
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Quote:
Originally Posted by B Dubya View Post
Scott, I understand the whole torque thing. Just don't understand how a 350 produces 700 or so in the torque range, then a 400 or 450 gets basically double that. I guess technology. I don't know enuff 'bout them to get any deeper than that!
The 350HP is a 6.7L engine and the 450HP is a 10.9L. Technology comes into effect when they take the same engine, and through programming alone, they go from 365HP, 660 FP to 400HP; 800 FP.
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Old 06-16-2016, 09:37 PM   #12
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Ours is 14.9L and the programming holds it to only 650 hp and 1950 ft lbs since the 4000MH is only rated for that. The Class 8 truck engines have less HP but more torque for use with manual trans or different automatics.
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Old 06-16-2016, 10:41 PM   #13
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Diesels and The Mountains

It is NOT torque which determines the speed you will go up a grade. It is HORSEPOWER.

The smaller 340 HP engine develops only 700 foot/pounds of torque, however it's maximum RPM is up around 2,500 to 2,600. The larger ISL and ISM engines maximum RPM is only 2,100, so they develop their maximum horsepower at a lower RPM. Since horsepower is a product of both torque and RPM, the smaller engine has to spin faster to develop its maximum horsepower.

The larger engine is definitely an advantage coming down those same grades. The smaller engines have an exhaust brake while the larger engines have a compression brake, also called a "Jake Brake." The Jake is a much more effective and powerful brake. We have the 400 HP Cummins ISL in our Mandalay. Using the Jake Brake, I never have to touch the service brakes coming down a 6% grade. I just shift down to 5th gear and come down the hill at a steady 65 mph. The Jake makes it very easy to descend those long grades.
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Old 06-16-2016, 10:49 PM   #14
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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.
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