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Old 09-15-2021, 10:08 AM   #1
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Power upgrade ideas Cummins 6.7

Hoping to tap the collective wisdom of this group! I have a 2018 Jayco Seneca on a Freightliner M2 chassis (2017 VIN on chassis) with a Cummins 6.7L. For some reason its rated at 340hp/600 torque, whereas the 2019 Seneca is 360/650. Is this the same engine that is in the RAM trucks, where the output is more like 390/800? I'm trying to figure out a way to coax some more power out of this rig without voiding my warranty or losing reliability. I've contacted Banks and a couple of local diesel shops but so far, no one has any ideas. One diesel performance shop said 'if it were my motorhome, I'd leave it stock'. Any suggestions? thanks in advance.
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Old 09-15-2021, 10:14 AM   #2
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Sometimes the lower HP/torque are to keep from damaging the transmission .

You current engine outputs might reflect the design spec of the trans and increase in power, could cause failure.

Do you have your trans model & specs?
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Old 09-17-2021, 10:53 AM   #3
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I know it's an Allison 6 speed, but I don't know what the specs are in terms of maximum hp; that's a good thought as to why they would 'de-rate' the motor. Sad though.
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Old 09-17-2021, 06:22 PM   #4
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Here are a couple of pictures .
First is a 2500 series 6 speed , and your engine should not be up graded .

Second is a 3000 series , 6 speed and would handle an up grade in engine power .

EDIT : Pictures posted in opposite order , trans with a stamped steel pan and external spin on filter is the 2500, finned aluminum is the 3000.
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Old 09-17-2021, 08:28 PM   #5
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That 340 HP rating is an excellent indication that you have an Allison 2500. That leaves you torque-limited and an upgrade is likely not a good option. I have this power train myself.
My engine and transmission combo has performed very well for 5 years and many thousands of miles. It accelerates well enough to easily merge with freeway traffic, and it cruises as fast as I want to safely go. I run between 8.7 and 10 mpg subject to winds and hills. Pulling the toad doesn't seem to make much of a difference to mileage or acceleration.
If you're looking for more power, it might make sense to move to a different coach. These are good days to sell one apparently, but not so good to buy one...
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Old 09-18-2021, 02:36 PM   #6
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this is excellent information; I'm going to head out to the storage facility this weekend to try and ascertain for sure which trans I have. There is conflicting information on Jayco's site regarding HP and torque figures are on each year. The Jayco information would suggest I have a 340/660 setup, which, according to the Allison website, would exceed the rating for a 2500MH trans (shows limits of 340/575 unless the unit has Shift Energy Management, in which case max torque goes up to 700. I'm not sure how to identify if an application has Shift Energy Management, so I'm still digging.
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Old 09-18-2021, 02:40 PM   #7
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Quote:
Originally Posted by Dark Sky View Post
That 340 HP rating is an excellent indication that you have an Allison 2500. That leaves you torque-limited and an upgrade is likely not a good option. I have this power train myself.
My engine and transmission combo has performed very well for 5 years and many thousands of miles. It accelerates well enough to easily merge with freeway traffic, and it cruises as fast as I want to safely go. I run between 8.7 and 10 mpg subject to winds and hills. Pulling the toad doesn't seem to make much of a difference to mileage or acceleration.
If you're looking for more power, it might make sense to move to a different coach. These are good days to sell one apparently, but not so good to buy one...
At first blush, I was inclined to think you might be right that the 340 hp rating suggested a 2500 trans, but I'm going to be sure. I did order a performance upgrade kit but I'm not going to install it until I make sure the trans can handle it. I live in the mountain west, and while performance is adequate, I find it lacking on the longer mountain passes pulling a Jeep Wrangler with a lot of off road mods, which adds weight of course.
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Old 09-18-2021, 07:55 PM   #8
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Allison HP and Torque pdf and another Allison HP/Torque chart.

Engine HP is designated by the MH mfgr. when ordered, not Cummins. This is IMO directly related to engine cost from Cummins, as increased HP is related to warranty terms and conditions.
I have an old ISC; I asked Cummins about a computer uprate out of warranty. $700 was quoted. I really doubt they will consider uprating an engine under warranty.

No it is not exactly the same engine Ram uses but I cannot explain the small differences. Even the Ram cab N chassis model uses a higher HP engine than the Ram full-body pickups.
When HP is near the upper limits of the Allison transmission, the Cummins ECM/TCM interface de-rates HP from a dead stop to reduce the possibility of transmission damage.


Your engine will perform adequately, you just will not be leading the charge up a mountain grade. The upside? You'll be getting 2-3 more MPG than the rest of the pack. Sit back, have a cold soda and think about the savings at the pump next fuel stop.
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Old 09-19-2021, 07:34 AM   #9
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That's an excellent Allison reference document. To the OP, it looks like you can hope to find a 3000 transmission in your bus. It looks like the horsepower limit is bumped up to 450. I'm sure it's going to be better to modify than to deal on another unit. Tennessee and Kentucky were no problem, but I haven't been out to the Rockies in ours. Without doubt I would be pulling in behind the tractor trailers crawling up the steeper hills.
If you have the smaller transmission it might be a good plan to just throw on the 4 way flashers, ease back and enjoy the great scenery. Best of luck with your plans!
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Old 09-19-2021, 08:03 AM   #10
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Cummins will uprate an engine under warranty, the cost to do so is more than if you do not want warranty coverage.
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Old 09-19-2021, 08:06 AM   #11
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Here is the info that Jayco published.
https://www.jayco.com/rvs/class-c-mo...ca/floorplans/
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Old 09-22-2021, 10:50 PM   #12
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Thanks for this information. I crawled under and my heart sank to see the spin on filter, indicating the MH2500. I verified this by typing the trans serial number into the Allison website. I found a ratings and specifications chart on the site as well, which indicates that the 2500 is limited to 340/575. However, there is a reference to Shift Energy Management, which ups the torque limit to 700. Problem is I haven't figured out if my trans has that feature, or if it can be added at a reasonable cost. I'm going to do some more digging before I give up and send my performance boost kit back to AG specialties.
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Old 10-07-2021, 03:41 PM   #13
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Cummins 6.7 and Allison 2500

A little status update: So I've determined for sure that I have a 2500 trans, not a 3000. The Allison website says a 2500 will handle 575 ft/lb of torque UNLESS it has something called Shift Energy Management, which I assume to be a software thing that keeps from bashing the trans with too much torque. With SEM, the rating increases to 700 torque. Now, to make it more interesting, a guy at the local Allison distributor told me that there are two 'maps' for shifting software, and there will be a switch on my shifter to toggle between them. He said he can reflash those settings to change the shift mapping, which in his opinion will address my power concern. Problem is, I've searched all over the shifter and the dash, and find no button to toggle. Anyone else on the forum heard of this, or know where else I might look?
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Old 10-07-2021, 09:37 PM   #14
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There are many people that have done the power update on the 2018 and earlier Senecas even with the Allison 2500. There are several threads about it over at the Jayco Owners Forum in the Super C section. There is also Allison reprogramming available that can make a big difference, everybody that has done it has been very pleased with the results. I fortunately have the 2018.5 on the S2 chassis with the 360hp and Allison 3000.

The Allison distributor might have been referring to the push button shifter on the 2018.5 and up, I believe the older units can only have one program loaded.

https://www.jaycoowners.com/forums/f...ate-68388.html
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