Cummins new 6.7 ISB vs the CAT C7

[directdrive]

we were thinking of making a change from our 2002 discovery to a newer discovery,we like the 2008 39r,but the new coach has the cummins isb 6.7 liter with 350hp and 760tq, our 02 has the c7 with 7.2 liter 330hp and 860 torque,looks like a heavier coach with a smaller engine,it also looks like the same engine they put in the dodge pickups.not sure it's good to have a truck engine in a motorhome.we really like the performace of our cat and are concerened the cummins just wont run as well. thanks for the help.

[Garbageman]

You will definetly notice the lack of torque between the ISB and C7. This will be a big issue if you drive in the mountains or tow anything over 3500 lbs. You would be better off upgrading to a coach with the Cummins ISC engine, like a Providence or Excursion if you want to stay with Fleetwood.

Paul

[directdrive]

i wonder why they didnt use the isc or just stick with the cat,it doesnt make sense to go backward with a smaller engine.

Scott.

[EngineerMike]

Money no doubt was the reason.
The Cummins engines will be more servicable over time as there are way more of them, especially now that Cat has quit the over-the-road engine market.
IIWM, I'd go ISC or ISL.

[Batman_777]

CAT will have to get back into the market...

I have the Cummins ISC 8.3L 360hp, 1050 torque... No Complaints

I heard the Cummins 400 and 425 are throttled back on torque since the Allison will not handle over 1200 anyway. So there's only 50 lbs of torque difference. And......
Side radiators are hydraulic cooled and take up to 70hp away from the 400hp to turn it. Rear Radiators are clutch belt driven and can at times take very little hp away from the motor. So I think the hoop-la over the larger hp motors is a lot of sales marketing to get more $$$.

[FleetMan]

"CAT will have to get back into the market..."
.
Because of government regulations, Cat made a business decision to get out of the "Over the Road" engine market. That was announced several months ago.

[Norm4015]

Quote:

Originally Posted by Batman_777 CAT will have to get back into the market... I have the Cummins ISC 8.3L 360hp, 1050 torque... No Complaints I heard the Cummins 400 and 425 are throttled back on torque since the Allison will not handle over 1200 anyway. So there's only 50 lbs of torque difference. And...... Side radiators are hydraulic cooled and take up to 70hp away from the 400hp to turn it. Rear Radiators are clutch belt driven and can at times take very little hp away from the motor. So I think the hoop-la over the larger hp motors is a lot of sales marketing to get more $$$.

Where did you get this information? 1200 lb ft of torque minus 1050 lb ft equals 150 and not 50.

My side radiator has a variable speed fan and it only goes to high speed at 210 degrees. In 35,000 miles of driving it has only got to that temperatture one time. The fan normally runs at a very low speed and uses very very little horsepower.

[directdrive]

are there any reliable ways to increase the torque of the isb 6.7?

[Batman_777]

Sorry... 1200 minus 1050 is 150 diff

[directdrive]

is there much of a power difference between the older cat engine and the new c7?
Thanks, Scott

[Garbageman]

When comparing old vs. new engines efficency is the big differences.
If an older engine makes 300hp/ 860tq and the newer engine makes 300hp/860tq the only difference is how efficent they make those numbers. A newer engine will probably make those numbers using fewer rpms and less fuel.

You also have to consider how much weight each engine has to propel. A lighter coach with an older engine might be more efficent than a heavier newer coach with the newer engine.

Are newer engines better, yes it most cases. Are older engines worse, no not all the time. Older diesel engines are work horses as long as they have been maintained and not abused.

Also a big consideration is the transmission attached to any engine. Older engines will have either a 4 or 5 speed, while a newer engine will have either a 5 or 6 speed. The more gears the better, IMO.

Paul

[directdrive]

we have the 330 cat (i think 3126) with the 6sp allison in our 02 discovery,it runs really well, even when towing. thought i read some where that the newer c7 did not run as well because of the new smog rules.

Thanks, Scott

[Triker56]

Quote:

Older engines will have either a 4 or 5 speed, while a newer engine will have either a 5 or 6 speed.

That statement is not always true.
My older 99 Discovery has a Allison 3060 6 speed with a ISB.
Pulling a Toad this summer it averaged 10.8 MPG over 4,000 miles.

Some of the newer MH's like the Fred and some DP, they are putting the Allison 2500 in them to cut cost.

[Garbageman]

Triker56, you are correct but I was thinking of the context of the OP. The transmissions are matched to a MH based on Torque, usually. The smaller engined FREDS can get away with the 2500 tranny. I think most DP's of the 80's and early 90's had the Allison 545 or 643 (I think I have the model numbers correct).

Your right about the Allison 3060 "World" transmission being used with ISB and 3126 engines of that era. I would bet today the manufacturers would use the 2500 because of cost and engine specs.

I guess we should define what is "older" before going any further with the OP. I own a 2000 DP and I don't consider it old but then the last 9 years have gone by like a blink of the eye.

Paul