HP ratings

[Cleeglog]

I'm familiar with smaller Cats and Cummins used in diesel pushers-most well under 500HP. Even million dollar buses seem to be limited to 500HP due to cooling and transmission limitations. I've heard with trucks you can have as high as 600HP. Which Mfg and How many liters is it ?

[Doug]

Right now, none, as they don't meet US emissions standards. I am guessing that the demand is simply not enough for the engine makers (Cat and Cummins) to invest in testing and certification.

The Signature 600 Cummins and Cat C16 are only useful to specialized needs such as heavy haulers, and much of their appeal for that market is the torque rating of 2050 foot pounds. That rating also takes one hell of a transmission. The Signature 600 is still available in Australia, where they run heavy combinations (wagon trains); I've seen it on the Australian Mack Trucks web site.

There are Cummins ISX, Cat C15, and Detroit Diesel (14L) motors which are rated up to 575 HP and 1850 foot pounds. These would be more than ample for any conceivable RV use.

One of the reasons you are less likely to see these higher ratings in the typical RV market is the transmissions. That market is concentrated in the typical dullard driver, who is not at all interested in driving performance, etc, and cannot and will not be bothered with anything but the easiest operating conditions. My recollection is that the typical (non-truck) automatic transmission in those units is maxed out at about 1650 foot pounds, which is actually plenty for the purpose - these are not heavy units, typically only about half the weight of a typical road semi.

My preference is for a Roadranger 13 speed; I think it is the most flexible and useful option for the majority of conditions. However, the co-driver issue for me would preclude that, leaving me with the autoshift 10s and 18s as the choice. Given the (comparatively) light weight of conversion RVs, I think the autoshift 10 will do virtually anything needed, and is probably the best return on investment. (In a semi, I think I would go with the 18.)

Each engine manufacturer has its adherents. The ISX 500ST looks like a heck of a good motor, with 500 HP, 1650 foot pounds, running up to 1850 in the top 2 gears. Honestly, though, that's more than needed; I would seriously consider specing that with an 18 autoshift in a semi if I had to go back to that life.

Likewise the corresponding C15 Cat, which seems to have taken a small beating from the emissions issue - the majority of their multi-torque ratings are gone. The advantage of the Cat to me is that in the C15, one gets not only a Jake, but their proprietary hydraulic retarder for additional braking power without using the service brakes. That alone might overcome the additional cost issue for me, since I am not likely to need the power.

In all honesty, though, a 11-12 liter motor with a rating of 400 HP or so, with 1450 foot pounds or so and a decent transmission, will do all one needs in this setting - other than the most extreme grades, I predict that there is little likelihood of a real drop in speed. The reduced load means that even this small engine is loafing most of the time, and longevity is not likely to be an issue unless you get a lemon. Fuel mileage will be better, etc.

You may be talking $10K or more increase in initial price, plus 1 or so MPG lost, to go the large power. It has real appeal, but little real value in an RV. Given the scarcity of real grades in most people's driving, and the fact that even those living in the most mountainous areas will spend little time actually needing the power, the big HP is probably not worth the additional cost and heartburn.

I drove a 28 foot Renegade with a FL-112 chassis. The transmission was a Eaton 10 speed auto shift. I don't remember the exact CAT specs, I am sure someone can help, but it was 400 and something and I believe 1400 lb ft of torque.

It was new unit at the dealer so the fuel tank was probably half full. No water or cargo.

If you are familiar with the Denver area we went up I-70 west. The first climb up to Genese is a good test but due to traffic I really could not get the full feel of the trucks power. So we drove west and turned back toward Denver at Floyd Hill.

East bound Floyd Hill is in the 7,000-7,500 ft elevation range and is at least a 6% grade. Part way up the hill I had to slow down because I was doing 70 mph and the speed limit is 65 mph. This is a favorite area for the state patrol.

I think that level of power is more than enough for most people. Even towing a heavy race trailer I think it would be fine.

[Gordy]

I spec'd a 2004 385 Peterbilt with a C13 Cat (435hp/1650 torque)with Freedomline 12 spd and all the toys and whistles. Thought to myself-why not put a C15 (475/1650) and be done with it. All the same options and for only $75 more gave me the big Cat.
No kidding-have the quotes to prove it. Floored both the salesman and myself.
Note that the torque rating is the same but the bigger displacment yeilds more hp at the same RPM.
Cat engine dealership didn't think there would be much fuel mileage difference as neither engine is being worked hard.

[John (C-IL)]

My son is an engineer for CAT in the engine controls division. I quizzed him over the weekend on engine sizes and he said the largest they offer is 550HP. He did say that they can go to 700HP with the current configurations, but most of those engines go in marine applications and heavy haulers. He said he could program an engine to be whatever you want it to be, but won't promise how long it will last or what the emissions would be. ;-)

[Doug]

And that ability shows some of the risk of not carefully specing the rest of the drivetrain. For example, in the note above, the Freedomline 12 speed has a maximum torque rating of 1650 foot pounds. Without even getting close to the risky area of making a crispy critter of the engine, it is possible to "grenade" the transmission if it is not rated for the power. A friend of mine saw a (Fuller) transmission let go on the dyno at a Mack dealer many years ago - it made a lasting impression.

The auto shift transmissions are the logical succssor to the old "Clutch-flite" of performance cars in the 60s and 70s (remove the torque converter, replace it with a clutch, leave the rest of the automatic transmission the same). I will give serious thought to the autoshifts, but would never have a full auto, just as I don't in my car. The only time I tolerate an auto transmission is in a squad car - and they don't stand up well to that use, either.

[vapoppa]

guys, my t2000 is a c15 with an eaton 18 auto shift an' it's a super set up. the single rear is the max limit for a c15. thanks. mase

[Doug]

Ok, now THAT I gotta see and test!

[Blue Skies]

Originally posted by Doug:
There are Cummins ISX, Cat C15, and Detroit Diesel (14L) motors which are rated up to 575 HP and 1850 foot pounds. These would be more than ample for any conceivable RV use.

Please forgive my ignorance about Cummins engines. What is the difference between the ISX and the ISM (and I think there is also an ISL)? What do those letters actually stand for?

Are the larger engines best matched with dual tandems or still OK with single axle conversions (a la onezman)?

Thanks.

[Gary Atsma]

The ISX Cummins is the 14-liter Cummins engine, while the ISM is the 11-liter smaller block Cummins. There was an L-10(liter) engine about 10 years ago but was replaced by the M11, which in turn was replaced by the ISM. If absolute max power(500+HP) is needed, use the ISX, otherwise find an M11, as it will give you much better fuel economy. Hope this helps you.
Gary

[Blue Skies]

There was an L-10(liter) engine about 10 years ago but was replaced by the M11, which in turn was replaced by the ISM.

That was helpful.
I've also come across in my reading something about a Cummins ISC? Is that also an obsolete engine?

What do all those IS_ letters actually stand for?

How important is the matching of the engine to the transmission type and number of drive wheels?

[Gary Atsma]

Man, you're really testing my Cumminsology!
Ok, the ISC is the next block size down from the ISM series, and is only put in some of the heavier medium trucks(Class 6-7), no Class 8's. It is not obsolete, but has been around about 18-20 years, and is fairly common mostly in medium Freightliners like the FL60 through the FL80. You got me on what the "IS" letters stand for, though. Call a Cummins Distributor. They MIGHT know(no guarantees on that one!).
Gary

[Blue Skies]

Cumminsology

IS_ Interact System is my best guess from the Cummins website.Cummins
Indeed there are the IS X,M,L,C and B engines in addition to the N14 and Signature 600.

Now to the next question, how to best select and match a transmission and number of drive wheels to an engine?

I sincerely appreciate the depth of knowledge this forum provides. Thanks.

[KAYE RIVERCITY]

....call 1-800-DIESELS Cummins will tell you everything you need to know about Cummins... B=5.6 liter model is the Dodge unite/// C 8.3 liter is the medium duty and military+RV amd Motorhomes/// M-11 is for small class 6 and 7 and 8's//// N=14 liter and ISX is the 625 hp big dog IIRC....geof kaye

[Gary Atsma]

Have they shrunk the B-series 6-cyl.? I always thought it was 5.9L, not 5.6L.
Gary

[KAYE RIVERCITY]

....maybe you are right....I'm OLD and forget!.....geof kaye

[HiRevs]

My motorhome a 1994 Monaco Dynasty (34') Was destroyed in a fire. The 8.3L cummins and allison 6 speed world transmission have about 36,000 miles on them. I put a Banks turbocharger on this rig as well. Any thoughts on the best place to sell these? the motor had 300hp and I don't recall the torque rating.

Mordy