Cummins HP questions

[Pudgy Camper]

Hi all, I'm currently in the market for a older 36-38' DP with a Cummins. But I'm confused by the different horsepower specifications for the same engine. I've seen ISCs with 300, 330 and 350 HP. And ISLs with 370 and 400. What determines the different HP within the same engine platform? Where some ISC/ISLs built with stronger internal parts? Or do some have extra mods or tuning to give it more HP?

Also, I was told that all Cummins ISC/ISL engines are capable of more HP/Torque with the addition of a tune. But I don't see alot of info or threads about that and wondering if its even a thing... or advisable. I've seen a couple DPs for sale and the ad says "chipped for 400 HP", not sure what that means exactly, but I think I would want to stay with stock HP to keep the long term reliability. Am I wrong or is this a common mod?

For years I've been into diesel pickup trucks, and with them we tune and heavily mod them mostly to increase reliability and drivability. But I'm guessing DPs are a completely different animal. Thanks for any input!

[Scepter40]

Think of it the same way as the 12V/24V/6.7 Cummins motors in medium duty trucks. More timing, more fuel, and more air in a mechanical engine results in higher HP and Torque numbers. In the 24V Cummins, folks had to add programming into that equation t get the same result. And when the 6.7 came around, same thing. It's all the same basic principle.

As to whether or not all are able to be increased with a tune, from what I've read, Cummins themselves can make that determination based on the current settings in the ECM. I wouldn't say it's common (again, based on what I've seen) in the MH world.

Personally, the issue I see with increasing the HP and torque in a MH is breaking parts. Transmissions are a big one. The Allison is rated for what it's rated for, and that's it. Also, there's not really a big resource like the medium duty trucks. Different camshafts, for example, are readily available for the 12V cummins in just about any configuration you can imagine. That's just not the case for an ISL. I'm sure there are sources, but they just aren't prevalent. In the medium duty world, jut about every transmission across the common manufacturers for 12V trucks (Dodge and Ford), there are entire businesses dedicated to building transmissions to handle high HP and torque.

[Skip426]

Any number of the HP differences you see can be the result of complete fuel delivery system changes, dictated by the year of production.

CAPS ( Cummins Accumulator Pressure system ) 1998>2003
An electronically controlled high pressure injection pump with mechanical injectors,
HPCR ( High Pressure Common Rail ) 2003 and newer.
Electronically controlled high pressure pump and electronic fuel injectors.
Parts pricing for the CAPS system is scary, given the system is 20 years old and a limited number of companies dealing in parts.

Both systems can be tuned ( chipped) for more power , Cummins approved HP upgrades, performed at a dealer, can be pricy, but depending on the engine year can be done without voiding warrantee .

[Pudgy Camper]

Originally Posted by Scepter40

Think of it the same way as the 12V/24V/6.7 Cummins motors in medium duty trucks. More timing, more fuel, and more air in a mechanical engine results in higher HP and Torque numbers. In the 24V Cummins, folks had to add programming into that equation t get the same result. And when the 6.7 came around, same thing. It's all the same basic principle.

As to whether or not all are able to be increased with a tune, from what I've read, Cummins themselves can make that determination based on the current settings in the ECM. I wouldn't say it's common (again, based on what I've seen) in the MH world.

Personally, the issue I see with increasing the HP and torque in a MH is breaking parts. Transmissions are a big one. The Allison is rated for what it's rated for, and that's it. Also, there's not really a big resource like the medium duty trucks. Different camshafts, for example, are readily available for the 12V cummins in just about any configuration you can imagine. That's just not the case for an ISL. I'm sure there are sources, but they just aren't prevalent. In the medium duty world, jut about every transmission across the common manufacturers for 12V trucks (Dodge and Ford), there are entire businesses dedicated to building transmissions to handle high HP and torque.

Thanks for the info Scepter, yeah I wouldn't feel comfortable just throwing a Banks tuner on and turning it up to level 5. Hopefully I can find a nice clean rig with a stock drivetrain, preferably ISL

[Pudgy Camper]

Originally Posted by Skip426

Any number of the HP differences you see can be the result of complete fuel delivery system changes, dictated by the year of production.

CAPS ( Cummins Accumulator Pressure system ) 1998>2003
An electronically controlled high pressure injection pump with mechanical injectors,
HPCR ( High Pressure Common Rail ) 2003 and newer.
Electronically controlled high pressure pump and electronic fuel injectors.
Parts pricing for the CAPS system is scary, given the system is 20 years old and a limited number of companies dealing in parts.

Both systems can be tuned ( chipped) for more power , Cummins approved HP upgrades, performed at a dealer, can be pricy, but depending on the engine year can be done without voiding warrantee .

Thanks for the info Skip, sounds like the CAPS is one component that you want to take care of. Must be why some guys add the Fass or Airdog lift pumps I'm guessing.

[vito.a]

When shopping for a diesel coach, ask what the engine torque rating is. It will tell you much more about the power of that engine.
An example is Cummins makes the smaller 5.9L ISB in a 350hp, the larger 8.3L ISC in 350hp, and the even larger 8.9L ISL in 370hp. The little ISB may only have 600 ft. lbs. while the ISC will be over 1000 ft. lbs. and the ISL will be 1100 ft. lbs. of torque.

[Pudgy Camper]

Originally Posted by vito.a

When shopping for a diesel coach, ask what the engine torque rating is. It will tell you much more about the power of that engine.
An example is Cummins makes the smaller 5.9L ISB in a 350hp, the larger 8.3L ISC in 350hp, and the even larger 8.9L ISL in 370hp. The little ISB may only have 600 ft. lbs. while the ISC will be over 1000 ft. lbs. and the ISL will be 1100 ft. lbs. of torque.

Good to know, thanks!

[153stars]

Don't know how far back your looking or models my M-11 is only 375 hp but 1350lbs torque at real low rpms. Too much for 3000 series Allison so needs 4000 series.
Maxing out HP on motors only increases torque a small amount or stock trans limits uprate you can give it. An Allison 3060 was kind if standard ,later years introduced lighter trans on ISB.
To get higher #s you needed to buy higher model not just pay for uprate or modify in some cases.

[jimcumminsw]

You will also need to consider the transmission at the higher/TQ numbers if you increase the current engine HP/TQ output.

Most engine HP/TQ numbers used in the motorhome is to provide a reliable Transmision life. The transmission ability to handle the HP/TQ may be the limiting factor for that model of motorhome.