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Author Topic: Towing capacity of the Cummins ISL 450  (Read 530 times)


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Towing capacity of the Cummins ISL 450
« on: January 20, 2018, 07:25:25 PM »
I'm new to the RV industry and looking for some feedback on the Cummins ISL 450 towing capacity.  I have a CDL A license and driven a variety of construction vehicles in my earlier years and understand the torque vs. horsepower comparison.  Recently i test drove an Entegra 45' coach but it was in Florida on flat ground, no fluids, no gear, nothing in tow and certainly no hills like we have in the Northeast.  My question is if the 1250 torque is enough to pull the coach fully loaded with an F250 in tow and hilly terrain.  I do know the Cummins 450 is in plenty of coaches and expect many have towing needs but i'd like to confirm it with some past or present users.  If it was the case of spending a few extra bucks to get the 605 and 1850/2050 torque i'd certainly do that but most of you probably know the engine is not an option.  Any feedback would be greatly appreciated. 


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Re: Towing capacity of the Cummins ISL 450
« Reply #1 on: January 20, 2018, 09:09:50 PM »
We don't have a Cummins engine, but we have a CAT C-12 with 425HP and 1550 lb-ft of torque.  We tow a ~3,400lb Honda CR-V and our coach (~34,000 lbs) never notices it is there.  We've driven ~55,000 miles in the past 8 years and have climbed some of the steepest grades in North America.  Don't forget that HP determines your speed when climbing a steep grade while torque OTOH governs how fast you move off the line from a stop. 

What you're considering is a heavier coach than we have with an engine with similar HP and less torque.  That translates into a slightly slower hill climbing speed and slower off the line performance.  On most interstate highways with their typical ~6% grade I can maintain just under 55mph; I would suspect that with an ISL you would be in the 45-50 range.  Is that bad?  Only you can judge if that's acceptable to you.  As for the lower torque, although I like driving my "sportscar" MH, even I will admit it's not essential.
« Last Edit: January 20, 2018, 09:13:33 PM by docj »
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Re: Towing capacity of the Cummins ISL 450
« Reply #2 on: January 21, 2018, 10:31:10 AM »
I have the 450 ISL in my 40' coach and am quite happy with the performance. Fully loaded and pulling my Wrangle Jeep Unlimited I am about 43,000 pounds going down the road. Speed up a grade is not too important to me, but this coach will pull grades in the west where I spend most of my time without issue. Do I slow down? Sure. Physics are what they are and builders can only do so much magic within those boundaries. My previous coach was a 36' coach with a Cummins ISC, and was rated at 380 HP and 1050 ft lbs.  My total weight in that coach was about 5000# lighter, but would climb the same grades, just 5-7 mph slower, and would have to downshift sooner and further. 

Many of the grades that the previous coach pulled in 3rd or 4th gear I now pull in 4th or 5th. My current coach is also rated to pull up to 15,000#.  That's a long way around to say that it's all relative, and it is much more important to me to get where I am going comfortably and safely, than being the first one up the hill.  In fact the more important feature in my current coach is the 2 speed jake brake that controls my speed going down a grade. 

Tiffin does offer the Cummins ISX with the 605 hp rated motor their bigger coaches, but it's a lot more than "just a few extra bucks". So the importance of speed and hill climbing ability is a personal choice for you to decide.  Is the 450 ISL a capable motor in a bigger coach? Absolutely. Is the ISX better?  Your choice.
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Re: Towing capacity of the Cummins ISL 450
« Reply #3 on: January 21, 2018, 07:12:33 PM »
It will drag the combined weight of the coach and a 10,000 lb trailer or toad over anything you will encounter on paved public roads. Whether you will be satisfied with the performance is something only you can decide.

I had the 370 hp version of the ISL in a rig that weighed around 37k lbs and when it came to grades over about 3-4%, the performance  was what I called "majestic".  It was smooth and never any doubt that it would do the job, but fast it was not. A long 6% grade might see me down to 35-38 mph. The 400 hp version was noticeably better with a near identical coach.
« Last Edit: January 21, 2018, 07:15:08 PM by Gary RV_Wizard »
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