Hi guys....I've been reading this board a lot and have gotten some good info from y'all. Haven't posted much though, because my questions usually get answered before I can ask them. Here is something I have been wondering about though...

Just wondering what RPMs y'all run while towing heavy loads. Our fiver is a 38 footer triple axle, and weighs around 17k, and I don't like to tow much over 65 mph. On a flat stretch of road, I am usually in 5th gear running 2500-2600 RPMs. If I shift to 6th, the RPMs drop to 1600-1700 RPM range. In fifth gear, I have no problem topping small hills without loosing speed. In sixth, I am downshifting a lot to keep from lugging the engine, so I decided to just leave it in fifth most of the time. It just seems like the 1600 RPM range is a bit low and lugs the engine a lot. If I push it up to 75 mph, the RPMs come up to around 2200 in sixth, but I don't like to run that fast with the fiver. All my guages say normal when towing, so I haven't been too worried, and I can still accelerate in fifth if I have to.

Is 2600 too close to redline for all day towing?

Thanks for your input...
Steve

 

I've got the auto but I run at 1900 @65mph pulling my 5VR with the cruz set in OD.
They say you run at 2200-2300 all day but I must agree, running at 1600-1700 does lug the engine when pulling a load.
If you run at 1700 most of the time without taking it out of 6th gear then it should be ok but if yo have to continually down shift then you need to keep it in 5th. Just my .01 worth

 

I only have a five speed and 3.55's in my truck, If I can keep it above 1750 rpms, it seems to run well and not lug. I dont know if this rpm is too low though. I think 1750 is about where the torque peaks.

 

Peak torque is from 1400-2900 but horse power climbs rapidly from idle to 2900. I know folks like to say you're supposed to tow at peak torque but when reality sets in, horse power is what moves us. I've had two 3.55 ratio trucks and two 4.10 ratio. The 4.10s outpulled the 3.55s easily. My '98 5spd with 4.10 ran 2500rpm at 70mph in O/D. It was noisy but unstoppable. My '03 runs 2350 at 70mph. Gas engines may have more horsepower but it's way up in the rpm. Diesels, although refered to commonly as torque engines, make higher horse power than gas engines at low rpm. My Cummins makes as much horse power at 1900 as a Hemi does at 3000rpm. When the load really gets heavy, the 600 makes as much horse power at 2900rpm as the Hemi at well over 5000rpm. The Hemi would have to run at over 3500rpm to do the same work as a 600 at a leasurely 2000rpm. So while not trying to get into a HP verses Torque aguement, we have peak torque along a flat powerband making horsepower at relatively low rpm compared to our gas counterparts. But it's still over 2000rpm where we get full boost and good horse power. And we can tow at a much lower rpm than a gasser in every equal situation saving fuel and noise.

 

I pull about the same load but with the 4.10 and have no problem pulling in 6th.What is your mpg pulling 17000# in 5th,I get 10mpg pulling in 6th.

 

Our last long pull was in April when we came from Idaho Falls, ID to Yuma, AZ. We averaged 8 1/2 to 9 mpg on that trip. Since then we moved from Yuma to Phoenix, but can't remember the mileage on that trip. When we did the long pull we barely had 4500 miles on the CTD. Still getting broke in. I think I could stay in 6th with 4.10 instead of the 3.73, but I do much more driving without the trailer than with, so I went for the 3.73 to try and get some mileage out of it. Now, I have about 6500 miles and am getting 18 without the trailer on the highway.

 

Radshooter,
60 mph in a six speed 4.10 is about 1900 rpms. I run all day at 1900 with a 36'er at over 16,000#. I will run down to about 55 before I shift if I am running on level ground and not trying to accellerate hard. 50 is still about 1700 rpm. You should be fine at 60, level ground, not accellerating hard. I usually shift out of 5th to 6th from a normal level ground take off between 50 and 55. My best mileage is between 52 to 55 - - 13.3 on the computer. It starts going down pretty quick from there up.
Bob

 

I looked at a few charts from links on another web site. They were for an '02 instead of my '03, but should still be close enough for my purposes. From the looks of things, horsepower and torque both peak around 2800 rpm if I read the graphs correctly. If I run 2600, that still gives me room to accelerate some, or pour it on for a hill without having to downshift to 4th. I remember back in grade school and high school when working fields with Dad's big tractor and being told over and over "Downshift if you have to, but NEVER EVER lug a diesel." I guess my old man wasn't so dumb after all Thanks Dad..The older I get, the smarter you were!

 

Nope. She'll be fine; but you'll pay a slight fuel consumption penalty. I've run 2500-2600 all day (unloaded) many times and pulled down 18-19 mpg.

4.10's would have been perfect for your trailer combo.

17K trailer. Jeez, I'm a lightweight with my boat - only 17K in total and I love the way it pulls with 4.10's. I normally run around 65 and get 13'ish mpg - and still have plenty of oomph to pass without downshifting.

 

Hey bulabula....I hear ya about the fuel consumption, but I didn't buy it for the mileage, I bought it for heavy hauling. I thought about the 4.10s, but we only pull the trailer once every 3 months or so, and I do tons more driving unloaded than loaded. I thought the 3.73 would be a good compromise, and so far I am very happy with it. If it was strictly a tow truck, that would be different, but it has to get me to work too after we park the trailer.
Thanks for the reply...
Steve

 

I run 2350 RPM @ 70 MPH towing our 16,000 lb GVWR 5ver (see signature). With the 4.10's and my current engine configuration, I only come out of 6th when I have to slow for curves or traffic. It'll hold 6th just fine on 6% grades.

Rusty

 

Thanks everybody....When we pull out of Phoenix after this contract, I think I will try more time in 6th and see what happens. It can't hurt my MPGs, thats for sure.

Thanks again....
Steve

 

Sorry to disagree but you couldnt be more wrong about HP and torque. Torque is what works for you (moves you) not HP. HP only tells you how fast the torque you have is working. Havent you ever seen a high HP engine that makes little torque? They have to work very hard to move you. And havent you ever seen a high torque/ low HP engine? They work great but are slow at getting the job done. An engine that builds lots of torque and lots of HP which follow along the same power curve are monsters. They work hard and they do it fast. HP generally comes with torque but torque doesnt have to come with HP. Do you think those big rig trucks can pull 80 TONS easily because the motors have around 300-400 HP or is it because they crank out 1500-2500 ft lbs of torque? HP by its self is way over rated but much used because thats what everyone loves to hear about, when in truth its really a good combo of the both working in unison.

 

I'm so sorry you don't know what you're talking about.
Torque is a static measurement of rotational force. A torque wrench doesn't measure how fast you turn a nut. It measures how much rotational force is on it. Torque X rpm / 5252 is horsepower. Horsepower is torque in motion.
Go to Cummins' website and look up motors for big rigs. They're rated in horsepower. You can use gear reduction to "make" all the torque you want out of any motor within reason. But the horsepower required to move a 40 ton truck at highway speed remains constant. A 400 horsepower motor will move a 40 ton truck down the highway. If that 400hp is at 1800rpm, then the motor will be efficient and able to produce high torque at that low rpm. If the motor makes 400hp at 6,000rpm, it'll still pull the 40 ton truck but it'll have to use gear reduction to make the necessary torque and will be inefficient and will wear out pretty fast. But both will do it. It takes 400hp to move a 40 ton truck down the highway. Obviously 400hp at 1800rpm is a lot more reasonable than 400hp at 6,000 rpm for a 40 ton truck. But it's still horsepower that moves the truck down the highway.
Rotational force is torque. The rate of speed of that rotation force is horsepower. Without horsepower you ain't moving.

 

OK, I'm not trying to get into a battle here, even though I do know exactly what I'm talking about, and I will say sorry for being a bit harsh when I claimed you couldnt be more wrong. BUT...
You basically repeated what I said about torque then went back to saying HP is everything then back again. I get what you are trying to say but I cant help but correct you. Torque is what you feel while driving. HP is only a calculation of torque. Torque is what moves a vehicle and you want to tow around peak torque. To keep from typing forever, look at one of the many sites where torque and HP are compared. HP vs. Torque Again, sorry if I came across as rude earlier.