300 HP Cummins Diesel

[fagnaml]

Vincee --


The 2007 Damon Astoria 3774 I had until three months ago had the 300 HP 5.9L ISB engine (pre-DEF engine) that performed well in the Texas Hill Country and climbing big bridges on I-10 in Louisiana. I asked my repair shop (RV Masters) in Houston if that engine could be "tuned" for higher horsepower and the answer was "yes" but they advised not to do so. Reason was the 300 HP ISB was coupled with an Allison 2500 MH transmission which is not rated for the higher torque from a higher horsepower engine.


What transmission do you have coupled with your 6.7 L engine? If you have an Allison 2500 MH transmission like I had, be sure the transmission would be damaged by higher torque coming from an engine tuned to provide more HP and torque.


My current Newmar Ventana LE has the 360 HP version of the 6.7L ISB engine coupled with an Allison 3000 MH transmission. The bigger engine is needed because the Newmar is 3 feet longer and 7,000 lbs. heavier than the Damon. The 6.7 L engine has performed very well thus far.

[vincee]

fagnaml, thanks for the info. My rig has the ISB 6.7L coupled to an Allison 2100 tranny. The work is being done right at the WNY Cummins Service Center, tomorrow. Before they could tell if mine was upgradable I had to supply them with the engine serial number which opened up a vault of info on my rigs set up. I wonder if the different Allison models have anything to do with the weight of the rig it sits in besides power?

[EZRider800]

Originally Posted by vincee

fagnaml, I wonder if the different Allison models have anything to do with the weight of the rig it sits in besides power?

Yes. The manufacturer will use the appropriate size Allison transmission based on the size of the vehicle as well as the GVWR and HP/TQ ratings of the power plant in the vehicle. The transmission and rear ends MUST be taken into consideration when spec'ing the engine in the vehicle or turning up the power in the current diesel engine.

[Farkey]

I have just recently purchased a 2002 Monaco 40' with a Cummins 350 diesel and while travelling in the hills of the Finger Lakes the other week, I found there was not enough hp/torque to keep me at 55mph. On more than a few occasions it slowed right down to about 40mph with my foot on the floor and dropping down gears.

But I think that was due to the weight it was hauling.

The coach it's self weighs in at about 30,000lbs and the towed car weighs in at just over 3,000, so that's a lot of weight to be hauling up hill.

And going down hill it wanted to get up to 70+, I was always on the exhaust brake and foot brake.

Quite an experience, but not a concern.

[A Traveler]

Increasing the horsepower does not necessarily mean an increase in the maximum torque.

A power increase comes by reprogramming the ECM to make the engine produce the more torque at a higher RPM. For example, the 400 HP ISL produces its maximum torque of 1,250 lb/ft at 1,400 RPM. But because that’s a fairly low RPM, it’s only 333 HP.
1250 X 1,400 / 5252 = 333 HP

As the RPM increases from there, the torque drops off slightly. The engine produces only 1,050 lb/ft of torque at its HORSEPOWER peak of 2,000 RPM.
1050 X 2000 / 5252 = 399.8.

If you can get the engine to produce 1,200 lb/ft of torque at 2,000 RPM, you now have a 450 HP engine.
1200 X 2000 / 5252 = 456 HP.

That’s a simplified explanation of how the horsepower rating can increase while the torque rating remains the same.

[SC40QS]

I've got the 400 ISL... what a beast! It will pull my 4500 lb toad at idle with the wheels locked.... yup... I did that...

[vincee]

SC40, at least you know you have "more power than you need" LOL!

[vincee]

Very satisfied with my upgrade to 360/800. Total cost was $357. Local Cummins shop had a free recalibrate with any service order, a $100 savings, plus they gave me 10% off for being a member of the Cummins Parts Club, I'm not. You really feel the difference on accelerating from a dead stop.

[sinterior]

Originally Posted by vincee

Wouldn't 100% torque at 0 RPM mean the engine isn't yet turned on or yet in motion?

Also, isn't that the exact reason trains run on GE electric engines and most if not all cruise ships.

Just the way electric motors work, yes they are "on" and full power can be applied before they even turn, hence 100% power or torque at 0 RPM.


I believe most rail locomotives are diesel/electric. Diesel engines generate electricity to run electric motors.

[A Traveler]

Originally Posted by sinterior

Just the way electric motors work, yes they are "on" and full power can be applied before they even turn, hence 100% power or torque at 0 RPM.

Not quite. No matter how much torque is on the shaft, if the RPM is zero, the horsepower is also zero.

[sinterior]

Originally Posted by A Traveler

Not quite. No matter how much torque is on the shaft, if the RPM is zero, the horsepower is also zero.

Ok, but my point was 100% torque, I was just trying to simplify, you need movement for HP, not for torque, simple mechanics really. Mechanics I understand, physics not so much, or at all really.

[k123911]

Originally Posted by paddler1954

We had an 08 with the 6.7L 325HP motor in a 36ft coach with a GCVWR of 43000 lbs. It would keep up with a traveling buddy's 37 ft V10 gasser that had a GCVWR of 27000 lbs. Neither burned up the road but adequate if you're patient.

And there in lies the problem... power always seems to be consumed by weight but why?
As you pointed out, your coach is shorter but weighs more hence it requires more hp and torque to perform at the same level. So again, why are diesels so much heavier?

[Ljwt330]

Originally Posted by k123911

And there in lies the problem... power always seems to be consumed by weight but why?
As you pointed out, your coach is shorter but weighs more hence it requires more hp and torque to perform at the same level. So again, why are diesels so much heavier?

Off the top of my head:


The ISB weighs nearly twice as much as the V-10, over 1100 lbs. vs ~625 lbs.


Coaches built with diesel engines are designed to carry more weight. To accommodate that ability, heftier axles, suspension components, often larger wheels, and chassis frames are used. Adding all those differences up will add more weight.


Keep in mind, we're talking about GCVWR. That includes towing weight, holding tank capacities, and storage areas. A vehicle that has the capability to carry 16K lbs. more weight is going to be build to a much stronger and heavier standard.

[deprived]

God, does every thread these days have to devolve into a pi@@ing contest?

To the OP - I have a 6.7/300 in my Tiffin. It's not a speed demon by any means, so if you're looking for that, the 6.7 isn't your engine. But it gets us from here to there with the MPG anywhere from 9-12 mpg, with 10 being our average.

We tow a Honda CRV, which is not supposed to be pulled faster than 65 mph so we rarely exceed that. Once, I let my attention wander and I noticed that we were easily going 82 mph! Thankfully there was no damage to the Honda transmission and no cops!! So the 6.7 is capable of a little heat, it just takes a while to get there. And, frankly, I don't think any motorhome should be driven much faster than 65mph, anyway.

I like that it is a very common engine so parts and service is no big deal.

We've entertained the idea of getting tuned to a higher HP but I don't think the transmission is rated for that.