Peak Torque RPM

[jdcosgrove]

Since I'll be dealing with my engine overheating issue while climbing steep grades in hot weather by slowing down, dowshifting, and increasing engine RPM, I thought it would be a good idea to re-read the section of the Cummins Owners Manual related to Engine Operating Range. It says not to operate the engine at full throttle below peak torque RPM for more than 30 seconds. It goes on to say the peak torque RPM can be found on the engine dataplate.

When I looked at the engine dataplate, all I found regarding RPM was in the box labeled "Advertised HP 350 at 2,600 RPM". I did not see anything regarding torque. Is 2,600 RPM the peak torque RPM? If so, what that tells me is that when climbing a steep grade at full throttle, I should be downshifting to a low enough gear so that engine RPM is over 2,600 RMP. Is my conclusion correct?

John

[Mr_D]

Cummins ISC .350 is 1400 rpm according to the Cummins chart I have. However you must have the ISB since you say 2,600 rpm is max. On the ISC it's 2,200 under power and 2,400 when the ebrake is engaged

On the ISB I have no idea on it.

Would help; if you gave us the year and model you're asking about

[TXiceman]

What they are telling you is to back out of the throttle and run a lower RPM and lower speed....They are concerned with engine melt down due to high exhaust heat. If yo do not have an exhaust temperature gauge, get one and drive by it.

I can run my Ford at 1100 degF for a long time, 1200 degF, better be backing off and 1300 degF...no way unless you want a new turbo and a few other parts.

Ken

Ken

[FleetMan]

Peak torque for your engine should be somewhere in the 1600 RPM range. However, you will need to get the correct data after determining exactly which engine you have and how it was configured and rated for your application. Running an engine under load below peak torque is classic "Lugging" which will result in engine damage of one sort or another. Down shift and try to keep the RPM well above peak torque RPM and you should be OK.

[jdcosgrove]

My engine is an ISB 6.7L CM2150, rated at 350 HP @ 2,600 RPM. It was built in late 2007 and is in a 2008 Itasca Meridain 37H.

[Steve Ownby]

Hey John,

Here is a Cummins publication on your engine:

http://cumminsengines.com/assets/pdf/4971104.pdf

According to this your rated torque peak of 750 lb/ft occurs @ 1800 rpm. Your engine has an extremely flat torque curve & is producing close to peak torque over a wide range of rpm at shown by the first graph on the right.

When hill climbing try to pick a gear that will keep you at an rpm just before the torque starts to fall off and a couple of hundred rpm below peak hp.

[Mr_D]

Quote:

Originally Posted by FleetMan Running an engine under load below peak torque is classic "Lugging" which will result in engine damage of one sort or another. Down shift and try to keep the RPM well above peak torque RPM and you should be OK.

According to the dyno chart the ISC 350's max torque (for a stock engine) occurs at 1400 rpm, below 1200 rpm is considered "lugging" it.
On the ISL 400 the dyno chart shows 1300 as the max torque and below 1200 is considered "lugging" it.

[macadnphyl]

On my ISC, the owners manual advises that 75% of governed max rpm
is ideal for maximum cooling under heavy loads. I run it at 1900, and
have had no overheating, even on long steep grades.

[Airtool]

John, Here is the Cummings Specks for the ISC 360. I have no info. on the 350 engine,it got to be close as it specks numbers you are posting.
Think page 2 gives the performance cures.

Dick

[PandK]

Attached is the data I got using my Silverleaf.

[J Walker]

I expect the OP has a rear radiator. Has it been cleaned regularly and is the slobber tube extended low enough? Do you know the procedure to spray Simple Clean on the inside of the radiator and blow it out with the engine fan?

[stik]

Quote:

Originally Posted by jdcosgrove My engine is an ISB 6.7L CM2150, rated at 350 HP @ 2,600 RPM. It was built in late 2007 and is in a 2008 Itasca Meridain 37H.

Just my "2 cents" but sounds like you have the same set up I have in my 2009 Journey. Why not let the Cummins and the Allison MH3000 handle it, just set the cruise control and let the ECM and the transmission work out the best gear?