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Old 12-17-2014, 06:18 PM   #15
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I'd be more concerned about torque than hp. Hp is calculated off the torque and rpm. More rpm, more hp. In our applications we're typically working at relatively low rpm even though the engine may be rated for higher rpm. Our mh gvw is 32K lbs. Our Cat is rated at 860 lb ft and I'd love a couple hundred more.

"Horsepower sells engines and cars. But torque moves the car." - Kevin McClelland, Flowmaster Mufflers
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Old 12-17-2014, 06:41 PM   #16
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Originally Posted by Dennis4809 View Post
I'd be more concerned about torque than hp. Hp is calculated off the torque and rpm. More rpm, more hp. In our applications we're typically working at relatively low rpm even though the engine may be rated for higher rpm. Our mh gvw is 32K lbs. Our Cat is rated at 860 lb ft and I'd love a couple hundred more.

"Horsepower sells engines and cars. But torque moves the car." - Kevin McClelland, Flowmaster Mufflers
As an old diesel man, I've always thought the same way. If I looked at 2 similar coaches with similar horsepower, one with an ISB @ 650lb torque, the other with an ISC @ 850lb torque, I'd figure that on a long hard grade, the ISC would do a lot better job.

Jim
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Old 12-17-2014, 06:49 PM   #17
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I was told that the ISB 6.7 340 has 660 torque? Was I mislead?
It may depend on the year. My 2010 ISB is 340 & 660.
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Old 12-17-2014, 08:31 PM   #18
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Cummins website shows the ISB peak torque varying from 520-800 lb ft. ISC is rated at 1050. These are based on a 2013 engine. Then there's the issue of a 2500 Allison with the ISB and the 3000 Allison with the ISC.
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Old 12-18-2014, 07:33 AM   #19
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As Steve says,the torque spec is the peak torque, so the ECM could limit what the transmission actually sees by limiting the RPMs so that they never reach peak. Allison says the 2500 MH can handle up to 700 lb-ft of torque with "SEM or torque-limiting", which is probably what Steve was referring to.

The ISB is actually capable of up to 385 hp and 865 lb-ft of torque, but the engine configuration used in motorhome applications is a max of 350 hp & 660 lb-ft (2015 spec).
6.7L Cummins Specs


Freightliner says it is delivering the XCS chassis with a 6.7L ISB at 340 hp and 700 lb-ft of torque, coupled to a Allison 2500 MH.
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Old 12-18-2014, 07:56 AM   #20
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Had an occasion to do a confrence call with both Spartan & Cummins on the line together to answer some questions regarding my engine brake. They both had to have my engine serial number and ECM serial number. Together they were able to confirm my exact set up and programing. While I had them both on the phone, also asked a bunch of questions regarding various items.

One of the items we discussed was the HP & TQ. Both Cummins & Spartan had the exact same response. Cummins delivers the exact same motor to all, each builder then in turn chooses what ECM and programing to apply. This is how you can have the same ISB in my case engine, with several different programing options all from the same builder.

My particual set up is 350HP & 750TQ, however I have a Allison 3000 transmission. For my 42ft rig, 95% of the time it is fine, no real complaints, but have been on some grade that left me wanting a lot more (Reno to Cali & Phoenix to Kingman) are two that recently come to mind.
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Old 12-18-2014, 08:01 AM   #21
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I just got off the phone with cummins - gave them my engine serial number and was told that the 340 hp is the max power for my motor. Cummins does offer a retro fit kit but each kit is custom made for the specific motor and they said it was expensive buy covered under warranty.
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Old 12-19-2014, 10:06 AM   #22
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It's in the torque

I'm intrigued by all the replies that overlook the lack of peak torque in the ISB relative to the ISC. HP means nothing if the torque isn't there when you it.

I did find instances where the ISC appears to be in coaches after 2010, although the Cummins catalog lists it as a 2010 engine. It is mostly missing after 2010 in brochures.

Also, my 2007 Ambassador, which at the time was the entry level diesel (I don't count the Vacationer) had an ISC with a GCWR of 43000 with 10000 towing capacity (33000 coach and cargo), the new Ambassador with the ISB has a GVWR of only 28000 and 5000 towing (23000 coach and cargo). So the difference in cargo carrying capacity (the big advantage in diesels) is not there.

I have lots of other issues with the new HR vehicles, which I didn't think Navistar could be outdone in, but that's another forum.
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