MPH Drop On Hills In Branson

[JohnJill]

I have a 350 Cat on the hills in Branson, Mo., pulling the coach and a car. It seemed like it struggled way to much on the hills. Would start out at 55 mph+ and would be at 45 mph when we would reach the peak. Is this a normal decline in speed?

[BillAdams]

Yep. However, not know what kind and size of coach you have leaves a bit of question but I would expect that this would be normal for most any similar setup. Be sure to gear down manually when necessary to maintain the proper RPM so the engine doesn't have to strain.

[wolfe10]

In a word, YES.

There are some very steep hills into Branson-- not long, but steep.

[JohnJill]

We are in a Itasca Meridian 39, Allison transmission.

[wildebill308]

Depending on the hill that's not to bad. Did you down shift? Did the transmission down shift on it's own? Were you in "econ mode"?

Bill

[andyshane]

I'd say it was to be expected. The C7 is okay for a 40-ish footer, but pulling a car will put you at a disadvantage on hills. Mine tended to overheat on those hills, the worst of which dropped my speed to 40-45 mph. (Driving a 40' Fleetwood Excursion, C7 Cat, pulling a dolly with a Honda Crosstour.)

[wolfe10]

To get the FACTS (i.e. based on physics) on how grades affect any heavy vehicle, please go to this Caterpillar Corporation document on the Diesel RV Club (an FMCA Chapter) Website.

The same physics applies irrespective of engine manufacturer. Please note that the HP requirements are HP AT THE REAR WHEELS which requires quite a lot more HP at the engine due to HP loss from things like alternator, cooling fan, loss in transmission and rear axle, etc.

IMO, setting reasonable expectations is the first step in driving any heavy vehicle, whether it is an RV or an 18 wheeler.

http://forum.dieselrvclub.org/index.php/topic,6594.0.html

[wajames]

Brett, the link works fine. Thanks! Good info

Andy, 6-7% grades with a 3126b/330hp ==> 2000 rpm in 3rd gear, 35 mph and the temp stays low, even on high hot days with a radiator that hadn't been cleaned in a couple years. On the flat - SilverLeaf shows ~10MPG at 62 mph

[hermanmullins]

One habit I have gotten into when driving where there are steep grades is just as I am getting ready to start on a incline I will step down on the accelerator.

This way I increase the boost to its max and I don't loose much power. It works most of the time (when I am paying attention) for me.

Herman

[JohnJill]

The motor and transmission worked like it should, was just curious since we were not on a actual mountain road like Colorado.

Thanks for your knowledge.

[wolfe10]

John,

Please take the opportunity to read through the document in the link in my post above.

Will go a long way toward your understanding what SHOULD happen.

[wildebill308]

The motor and transmission worked like it should, was just curious since we were not on a actual mountain road like Colorado.

Thanks for your knowledge.

Please explain the difference between a 8% grade in Mo. and the same grade in Co. Read the links Brett posted and you will have a better knowledge of what to expect.

Bill

[xctraveler]

In my experience there are plenty of steep grades east of the Mississippi, some steeper than what you will find "out west in REAL mountain country" Indeed the steepest highway grade I've driven, not in my coach, was at the far eastern end of Gaspe Peninsula (that's Quebec) descending into Perce, the grade was marked 16%, was a couple of miles and ends with a 90 deg turn into a shopping street. The other alternatives are all wet. So much for mountain grades. Never saw anything quite that steep in the Rockies, although those grades tend to be longer.

I am always grateful to be moving forward at the top of a long steep grade, until I face the descent on the other side.

[desertdeals69]

Please explain the difference between a 8% grade in Mo. and the same grade in Co. Read the links Brett posted and you will have a better knowledge of what to expect.

Bill

It has to do with the air pressure. Less air at higher elevations.

[wolfe10]

It has to do with the air pressure. Less air at higher elevations.

Very true if we are discussing normally aspirated (non-turbo) engines.

But, with the OP's Caterpillar C7, it is rated for full HP up to 10,000'. Basically the turbo "makes it own air" and compensates for the altitude.

[desertdeals69]

I notice that my ISB seems to have less power at elevation even at 28 lbs of boost.

[wildebill308]

What year is your ISB? You don't have it in your profile. Have you checked all your connections for leaks?

I pull 35-36 pounds of boost when it's working hard.

Bill

[rebootsemi]

If you want to give your motor a workout take I-70 west out of Denver its all up hill until you hit the Eisenhower tunnel at 11K ft, then down for about 8 miles but man it sure is pretty.

[dickandlois]

I notice that my ISB seems to have less power at elevation even at 28 lbs of boost.

DD sounds like you have a waste gate setup on your turbo with fixed turbine blades, common on the earlier ISB, like the one on my Cummins.

It does fall off some at about 10,000ft.,but we do not spend much time driving at that altitude. I do like the simplicity of the system though.

The VGT style turbos are not affected by altitude.

Rich.