Driving With Torque and a dead lift pump.

[bobrw9]

I’m a SilverLeaf kind of guy and browsing their web site I found the following article.

This from the spring 2001 newsletter, Tip of the day- What is torque and horsepower?
Every vehicle could use a gauge on the dash that simply
said “Performance”. The Torque gauge is certainly the
closest equivalent available on any machine. When
performance matters - hill climbing, for example - drive to
maximize this reading. In general that means working the
engine in its optimum power band - which for most diesels
is the lower end of its rpm range. You can see this
explicitly with the Torque gauge - as rpms increase,
performance goes down, and more fuel is burnt to less
effect.
When simply cruising at low load, the Torque output will
normally be well below peak levels, and the gauge will not
be particularly relevant. The gauge is meaningful mostly
in high-demand situations - accelerating and climbing.

The coast of Oregon, HWY 101, is a great place to check out “Driven with Torque”.
We spent the month of July cruising up and down the coast.
Find the right gear for around 1500 RPM and my ISL 400 will produce 1760 foot pounds any time, any day.
It’s rated at 1800 so I can’t complain.
BUT
The first week of August my Lift Pump failed.
It was the new model pump with less than 18000 miles of use.
18000 miles doesn’t sound like a lot of miles for a lift pump.

The lift pump is a low duty cycle unit and I’m wondering if all my “Driving with Torque” and charging up all those hills caused a lot of ware-and-tear on the pump thus producing an early death?

[camping fam]

I have done alot of reading on lift pumps and recently changed mine i replaced mine with a stock unit using the cummins relocation kit. Now with that said I am all about using factory parts BUT after looking at this situation I will prob replace it with a aftermarket one that you can turn up a bit. Our pushers are a great thing but when you have a little pump sucking 30+ feet with heat and whatever else it can get real weird real fast.

The best thing i did was install a fuel pressure gauge i watch it and make sure when i am pulling a big hill i back out of it a bit to save a little on the pump. The fuel gauge was less than $100 and money well spent in my mind.

[wb7auk]

Lift pumps for diesels are continuous duty pumps.
In diesel engines the fuel is pumped to the engine and unused fuel
is returned to the fuel tank.
One of the reasons for this is keeping the fuel cool and to cool the
injectors.

[greystroke]

Also a Siverleaf guy with a gage installed to measure lift pump pressure. Just recently replaced mine prior to failure because the pressure was too low. I used a stock pump from cummings but also did some research on the FASS pump. The idea was to mount the Fass on the frame. If my new lift pump fails that is what I will do. Just completed a 3500 mile trip without incident. Time will tell. The danger of running low lift pump pressures is damage to the injection pump.

[Rich-n-Linda]

Here we go again...

It is NOT torque that gets you up the hills at speed. It is HORSEPOWER, which is a combination of torque and RPM.

Yes, as the RPM goes up the torque number will go down slightly, however the increase in RPM offsets the drop in torque and results in the engine producing more HP at the higher RPM.

Lugging your engine up long grades at low RPM can cause overheating problems. When climbing grades you should have your engine RPM up at the HP peak, not down at the torque peak.


Rich & Linda
'06 Mandalay 40E
Freightliner XC-R chassis
Cummins 400 HP ISL

[wb7auk]

Torque equals force and Horsepower equals time, (the amount of time to apply the force)
A diesel engine is most efficient at torque peak or a little above. However if one has
cooling issues increasing the RPM will help with cooling but will also increase the fuel
usage and will get you up the grade a little faster but at a cost.

[Steve Ownby]

"Find the right gear for around 1500 RPM and my ISL 400 will produce 1760 foot pounds any time, any day. It’s rated at 1800 so I can’t complain."

I agree with you that if you are looking for torque that 1500 rpm for a Cummins ISL is a good spot. However I have never seen a Cummins spec listing the ISL at over 1250 foot pounds of torque at the flywheel and that is for the 2010 version.

Here is a Diesel engine "sweet spot" calculator I picked up somewhere. While climbing a grade at torque peak may be most economical from a fuel burned stand point, I submit that your engine will be less stressed and you will be less of an obstruction to other traffic at the "sweet spot".

Diesel Engine "sweet spot" ISL

HP X 33,000 = A
Torque X 6.283 = B
A/B = sweet spot rpm


ISL
HP 400
TORQUE 11200


A: 400 x33,000 = 13,200,000
B: 1200 x 6.283 = 7540
1,750 sweet spot rpm for Cummins ISL




Steve Ownby
Full time since '07

[camping fam]

With your silverleaf you can monitor fuel pressure what is pressure averaging?

[docj]

Originally Posted by bobrw9

Find the right gear for around 1500 RPM and my ISL 400 will produce 1760 foot pounds any time, any day.
[FONT=Calibri]It’s rated at 1800 so I can’t complain.

The torque spec for an ISL 400 is in this document. The engine is rated at 1200 ft-lbs of torque.

http://cumminsengines.com/uploads/docs/4971107.pdf

[DMTTRANSPORT]

Originally Posted by Rich-n-Linda

Here we go again...

It is NOT torque that gets you up the hills at speed. It is HORSEPOWER, which is a combination of torque and RPM.

Yes, as the RPM goes up the torque number will go down slightly, however the increase in RPM offsets the drop in torque and results in the engine producing more HP at the higher RPM.

Lugging your engine up long grades at low RPM can cause overheating problems. When climbing grades you should have your engine RPM up at the HP peak, not down at the torque peak.


Rich & Linda
'06 Mandalay 40E
Freightliner XC-R chassis
Cummins 400 HP ISL

You are Correct, Torque gets things moving, HP keeps it going

[Jeff753]

What is the sweet spot for a 2001 Cummins 350hp ISC

Originally Posted by Steve Ownby

"Find the right gear for around 1500 RPM and my ISL 400 will produce 1760 foot pounds any time, any day. It’s rated at 1800 so I can’t complain."

I agree with you that if you are looking for torque that 1500 rpm for a Cummins ISL is a good spot. However I have never seen a Cummins spec listing the ISL at over 1250 foot pounds of torque at the flywheel and that is for the 2010 version.

Here is a Diesel engine "sweet spot" calculator I picked up somewhere. While climbing a grade at torque peak may be most economical from a fuel burned stand point, I submit that your engine will be less stressed and you will be less of an obstruction to other traffic at the "sweet spot".

Diesel Engine "sweet spot" ISL

HP X 33,000 = A
Torque X 6.283 = B
A/B = sweet spot rpm


ISL
HP 400
TORQUE 11200


A: 400 x33,000 = 13,200,000
B: 1200 x 6.283 = 7540
1,750 sweet spot rpm for Cummins ISL




Steve Ownby
Full time since '07

Jeff
2001 Dynasty Regent tag axle
Cummins 350 8.3 ISC

[Steve Ownby]

Originally Posted by Jeff753

What is the sweet spot for a 2001 Cummins 350hp ISC









Jeff
2001 Dynasty Regent tag axle
Cummins 350 8.3 ISC

If your ISC has a max torque of 1050 foot pounds and is 350 hp then you just plug those parameters into the formula.

HP X 33,000 = A
Torque X 6.283 = B
A/B = sweet spot rpm


ISC
HP 350
TORQUE 1050


A: 350x33,000 = 11,550,000
B: 1050 x 6.283 = 6597
1751 sweet spot rpm


Steve Ownby
Full time since '07

[Smitty77]

I was on a Droid Only (And I admit I have problems typing on a Laptop, let alone a stinking Droid keyboard!!!!), so did not respond to the OP as Steve did. Suspect the OP had a typo on the stated torque of his ISL, as I don't thing ISX's have those numbers on RV's!

ISL's come in many flavors. CAPS, Common Rail with VGT (Variable Geometry Turbo), Commons Rail VGT DEF equipped, and probably others I missed in this listing.

Each one will have a different 'Sweet Spot', but also each one could be accompanied by different Gear Ratios by the various Chassis builders.

Steve's provided formula, works pretty dang well from my drivers seat referencing. This is in a CAPS 2003 Era Engine, in a 2004 model Country Coach.

I usually find the best combo of 'pulling a hill' and MPG economy between the 1675-1800 RPM range, based upon Silverleaf. I've also noted the Silverleaf HP reflects between 350-370 within this RPM band, and my ECM is 'flashed' to keep my engine maxed at 370HP. On Silverleaf, I used to show constant displays of 1) Torque, 2) HP and 3) Current MPG. After a few years of watching the MPG, I now change that setting around from time to time, as it I found it less meaningful to my driving enjoyment!

Neat formula that Steve provided, and good to play with as general info. But Steve will be the first to tell you that the combo of engine, gear ratio, and overall weight of rig - will have influence on this 'General Formula' in relation to your coach.

Have fun, enjoy your rigs, and who cares if it takes me two minutes longer to get up a hill then someone else? I know I don't...

Be safe,
Smitty

[road dogs]

Not a MH owner, but I drive my TV by EGT regardless of any other parameter. If I'm climbing a steep grade and EGT starts climbing, I downshift and try to keep RPM around 1800 or higher if necessary.