450hp ISL going up hill

[tomakat]

I'm new to driving a DP and would like recommendations on the best way to maintain power going up hills. Am I supposed to downshift manually and/or keep it within an certain RPM or floor it and let the Allison transmission manage the gearing?

[Mr_D]

Either way works. The Allison is smart but if it starts to heat up you need to back off and downshift. The best economy is low rpm, high boost and high throttle according to Cummins. Best climbing is high throttle, high rpm so gear down.
When we had the ISC 350 with Banks in our Dutch Star I almost always let the Allison do it's thing and didn't use the "economy" mode in the transmission in the hills. With the Magna I can leave it on cruise and in "economy" mode almost all the time. Different engine, totally different torque curve and far more of it even though it weighs 8 tons more than the DSDP did.

[Skip426]

Here's what came with my coach , and this works for me.

[britcon]

Our Ventana has the 400 ISL. Initially I tried downshifting on grades. I found I am better off trying to hit the bottom of a hill between 60 & 65 and just letting the computer handle things. Only issue is when you get behind a slower vehicle and loose momentum, then you might want to manually shift.

[tomakat]

I went up a steep incline and I downshifted from 6th gear to 4th gear near the bottom of the hill while pulling my Jeep Wrangler Unlimited. I previously could do this hill in my 34 ft. v10 gasser (with Ultrapower upgrade) doing around 50-55. With my Cummins, I dropped down to 45mph. Of course I was expecting to be equal or better than my 2009 Ford v10.

[Mr_D]

I've seen several owners posting about the same "problem" with their DSDP's. Seems like the ISL is just not up to the weight the new/larger DSDP's carry. That was one reason for not wanting another DSDP even though the DW fell for a 4375 about ONE HOUR after we signed the papers for the Magna. My mistake for letting her see it!
With the 2002 4090 we had I waited about 4 years and installed the Banks kit. That did make a big difference in it but still lost speed in the hills. But it certainly was better than the '98 35' Santara with 460 and Banks kit or the 2000 38' DSDP with CAT 3126!
But how much did the gasser weigh compared to the DSDP? How does the DSDP compare to the stock gasser since you "hot rodded" it? The ISL 450 is right at the top of what the 3000 MH is rated for, in fact I suspect it's tuned to it's max for dependability with that combination.

[Dutch Star Don]

This is long, but it will give you an idea what I do and what I've found with my ISL. I've had two ISL's. The first was a 400 in my 2005 Diplomat that weighed in at about 32K. I let the Allison do the thinking for the first year or so, but then started dropping to 5th manually at the base of any grade that was 5% or better. I later chipped the engine and changed out the rear engine fan and the coach became a ROCKET. I could pull the Grant's Pass grade in Oregon or the Grapevine in California easily, while towing my 4 door Silverado, at 60 mph plus. Even then, I always dropped to 5th gear.

Fast forward to the Dutch Star with the 450 ISL and weighing in at 42K, 47K with my truck. I almost cried on the first grade I pulled. The extra 10K really slowed down the coach. I also found that the coach was geared a lot differently. I still manually downshift to 5th at the base of large grades, but find I need something just between 4th and 5th. 4th gear requires me to slow to 50mph max.

So......the ISL 450 in the Dutch Star isn't a hill gobbler, but I find that I can do okay with a little more "driving input". My Diplomat was just a brute and would climb in 5th, while in cruise control while I relaxed. With the Dutch Star I accelerate a little more before the grades, shift a little more and pay more attention to what rpm's I'm running. Since doing this, the Dutch Star has done much better. It's a little more work mentally, but has helped, and stopped me from crying as much.

I intend to chip the Dutch Star next year and see how it does, I want to get 20K on the motor before I add the chip. The chip, DigiCr, won't add more HP, but seems to widen the power band and produce more HP in the mid range. The DigiCr chip reverts to stock at wide open throttle. I'm curious to see if it will help the Dutch Star.

Hitting the 12K mark on mileage has seemed to loosen the engine a little and provided more HP. My Silverleaf was estimating my HP on some climbs at just over 425. On my last trip, I hit 445 on two occasions. I saw 1225 torque briefly too. So things are getting better after the 12K mileage mark. We leave for Yellowstone on Monday and will be pulling the Baker grade into Vegas. I'll see how it does.

[Mr_D]

The Silverleaf "estimates" on HP and torque are all done with the programming. They took the engines dyno info and programmed that into the VMS. It has very little meaning other than to give you something to look at. That comes directly from the SilverLeaftech support site when I asked about it.

[Gordon Dewald]

Our ISL seems to work OK. With only 6,000 miles on it I am working it but not pushing it. With the trailer we are 48,000.

In the hills I take it out of econo mode and let the transmission do the thinking.

I have tried shifting a couple times and will be doing more as time goes on. Just a matter of getting comfortable with the performance, especially when the engine loosens up.

[tomakat]

Originally Posted by Dutch Star Don

Fast forward to the Dutch Star with the 450 ISL and weighing in at 42K, 47K with my truck. I almost cried on the first grade I pulled.

Thanks for the chuckle, Don.

My 2015 DS4018 only has 2300 miles on it and most of that was from it being driven from Nappanee to Tom Lindstrom's lot. On the flats, I love the power of the 450 ISL with the freightliner chassis, IFS, and comfort drive. It's so smooth and quiet. So much different than sitting on top of the Ford v10 that I just traded in.

I tried one hill and let the Allison do its thing and it performed admirably pulling my 4 door jeep. On a very steep grade I thought I would do the manual shifting to see if I could get better performance. I think I shifted too late since I was going uphill already and I probably lugged the engine a bit....hence 45 mph. If I were to do the manual shifting, should I start off by downshifting from 6th to 5th?

[PanJH]

All good info.... we are going to head west this summer and will be in much more severe grades than we are accustomed to here on the east coast.
What target RPM do you usually shoot for when climbing a steep , long hill ?

[dakotabuckeye]

Originally Posted by PanJH

All good info.... we are going to head west this summer and will be in much more severe grades than we are accustomed to here on the east coast.
What target RPM do you usually shoot for when climbing a steep , long hill ?

Maximum torque is 1250lb-ft @ 1400 RPM’s. I suspect you would want to hit the bottom of the hill with as much momentum as safely possible and try to maintain 1400 RPM’s. In about a week I’ll be putting this theory to the test. Next Tuesday we pick up our new Dutch Star and by next Friday we’ll be crossing the Big Horn Mountains in Wyoming on our way to Yellowstone. This is a trip we made many times in your 2007 Winnebago Sightseer with the Ford V-10.

[96 Wideglide]

I think you'll be lugging the engine trying to climb a long steep grade at 1400rpm. These motors put out max HP at about 2100rpm. I climb hills at 1900-2000rpm. Easy on the motor, and keeps it cool due to high water pump speed.

[Mr_D]

Best fuel mileage is with high throttle opening at 200 rpm over peak torque rpm. Best climbing speed is with rpm near HP peak. Those are gleaned from Cummins documents over the years.