Driving lesson needed

[deandec]

The below chart is from Banks Power Pack web site and is used here only to frame a driving question. (sorry I could not figure how to import the image.)

http://assets.bankspower.com/prod_in...M01_B59_TQ.gif


My focus is the black line that shows the rear wheel torque on my stock C8.3L Cummins engine. A Minor difference is that I have the 300 hp engine and the chart is based upon the 250 hp engine.

When driving up a 6% grade on warm days, I typically shift down to keep my engine at 2000 rpm and keep the water temp at 200 to 210 degrees.

The chart above indicates that once I exceed @ 1600 RPM I begin losing Torque and at 2,000 RPM will have lost 30% of the torque available.

Questions:

Am I a better driver if I let the engine lug at 1600 rpm for max torque or spin it to 2000 rpm to keep it cool? Or, is there something wrong with the above chart?

[Mekanic]

Quote:

Originally Posted by deandec The below chart is from Banks Power Pack web site and is used here only to frame a driving question. (sorry I could not figure how to import the image.) http://assets.bankspower.com/prod_in...M01_B59_TQ.gif ...... Questions: Am I a better driver if I let the engine lug at 1600 rpm for max torque or spin it to 2000 rpm to keep it cool? Or, is there something wrong with the above chart?

Kepp it cool no matter what!! @ 2000 RPMthe HP is coming up also so it so the chart is I think slightly misleading.
Funny how they left the HP off the chart.

I worked for a company 20 years ago that made high performance Camshafts.
I have seen more than a few Torque/Horsepower charts. These things are like most advertisments and taken with a grain of salt. Some I have seen are downright fiction.

[deandec]

I guess I left the HP chart off of the link:






You are correct, the HP does rise slightly as the RPMs rise.

[Route 66]

You do not want to lug the engine. Keep the RPMs up for the horsepower and better cooling.

Quote:

Originally Posted by deandec When driving up a 6% grade on warm days, I typically shift down to keep my engine at 2000 rpm and keep the water temp at 200 to 210 degrees. Questions: Am I a better driver if I let the engine lug at 1600 rpm for max torque or spin it to 2000 rpm to keep it cool? Or, is there something wrong with the above chart?

[Midniteoyl]

Quote:

A Minor difference is that I have the 300 hp engine and the chart is based upon the 250 hp engine.

[Mr_D]

Quote:

Originally Posted by Route 66 You do not want to lug the engine. Keep the RPMs up for the horsepower and better cooling.

If the chart starts at 1,600 rpm then running that RPM is not "lugging" it. The Allison shouldn't allow it to lug.
If it starts to overheat then you will need to downshift and get the rpms up.

On our ISC with Banks I run in the economy mode most of the time. I very seldom turn it off and have never had an overheating problem. But we've got a side radiator and hyd fan too. That would make a difference.

[Gary RVRoamer]

You will notice the horsepower is pretty flat from 1700-2100, assuming your engine has the same torque/hp curve (bad assumption, but it's probably fairly close). So as the RPMs increase, torque falls a bit but the higher RPMs keep the hp increasing and you climb the hill nicely anyway, thank you! Bottom line is that anywhere in that range is fine for performance, but higher RPMs probably help the coolant flow and fan speed, so a bit higher is generally a good thing when climbing a hill. You aren't "lugging' at 1600 RPMs, so no need to worry about that.

I would keep an eye on the temp gauge and vary the RPMs upward enough to keep the coolant temp in range, definitely under 210 and hopefully down toward 200 or less.