RPMs while towing
11-08-2004, 09:05 PM
#31
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Rats... just my luck. 63 years wasted, could have just asked you instead of all the experience. 
Hannabal I never got into water wheels, you are probably right.
Hannabal I never got into water wheels, you are probably right.
11-08-2004, 09:22 PM
#32
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Yeah but just think of the newfound knowledge you'll get to use for the next 63 years!
The water wheel is an extreme but it does make the mathmatical point pretty well. In my 43 years I've towed with and owned several gas and diesel vehicles. I've found that the gas engines of comparable horsepower usually have to run a gear lower to do the same job as my diesel and had a fantastic cleaning ability when it came to my wallet. All my vehicles have been bone stock so my experiences are based on stock power. Your Cummns is definately not going to lay down for any gasser by looking at your sig.
The water wheel is an extreme but it does make the mathmatical point pretty well. In my 43 years I've towed with and owned several gas and diesel vehicles. I've found that the gas engines of comparable horsepower usually have to run a gear lower to do the same job as my diesel and had a fantastic cleaning ability when it came to my wallet. All my vehicles have been bone stock so my experiences are based on stock power. Your Cummns is definately not going to lay down for any gasser by looking at your sig.
11-09-2004, 04:33 PM
#33
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For what it is worth, beyond the HP/Torque/Calculus Doctoral thesis, I think 2000 rpm is a fairly good medium to give some boost & HP, as well as decent fuel economy. Our rigis about 36', 13-14k & 12' high, also a mileage factor. We get 11-12. If towing flat ground or nearly so, 1800 RPM works OK if I am not in a hurry. As your speed & RPM's go up. so does fuel comsumtion. You might try 2000 RPM to see if you get better speed & mileage, vs gearing down to 5th. We have 4.10's, which are perfect for Heavy loads & 55-60 mph. At 2000, you may only occasionally need 5th for hills, not too bad, maybe.
11-10-2004, 12:19 AM
#34
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I'm at a loss.
First you said,"I know folks like to say you are supposed to tow at peak torque but when reality sets in, HP is what moves us."
Then I say "no", "HP is only a calculation, and you feel torque. Torque does the work and HP is a calculation of how fast the torque is working." HP and torque work together.
Then you say I'm wrong and claim all engines can do the same job, it just depends on gears.
I dont see Haulin in Dixie running a Hemi. Why? Because your argument is all about gearing, not engine output. Besides the topic question is about "What RPM is OK to tow?" Hense, what RPM is the Cummins best to tow with. Well now after hearing your theory I'm going to contact DC and advise them to loose the Cummins and slap in a electric motor mated to a constant variable tranny and let it spin around, oh lets see, 30,000 rpm so as to get the maximum torque-opp... I mean HP to tow with.
First you said,"I know folks like to say you are supposed to tow at peak torque but when reality sets in, HP is what moves us."
Then I say "no", "HP is only a calculation, and you feel torque. Torque does the work and HP is a calculation of how fast the torque is working." HP and torque work together.
Then you say I'm wrong and claim all engines can do the same job, it just depends on gears.
I dont see Haulin in Dixie running a Hemi. Why? Because your argument is all about gearing, not engine output. Besides the topic question is about "What RPM is OK to tow?" Hense, what RPM is the Cummins best to tow with. Well now after hearing your theory I'm going to contact DC and advise them to loose the Cummins and slap in a electric motor mated to a constant variable tranny and let it spin around, oh lets see, 30,000 rpm so as to get the maximum torque-opp... I mean HP to tow with.
11-10-2004, 06:59 PM
#35
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Yep. That's what I said. The new 600 Cummins makes over 200 horsepower at 1800 rpm. The Hemi makes just over 100 HP at 1800 rpm. Drop out of O/D with the Hemi and it'll be making just over 200 HP at around 3,000rpm. Drop out of O/D with the Cummins and you're at peak 325 HP. That's why the Cummins is better for towing. It makes more HP down in the rpm range we like to run in. If I were towing our 10,400 lb 5th wheel with a Hemi, I'd be looking at 4,000 +rpm quite often. It would do it but that's not what I want.
I don't feel torque in my truck. I feel HP. Torque is a static measurement that doesn't envolve movement. Torque being applied at increasing rpm (horsepower) is what I feel. When I'm climbing a grade, Peak torque at 1400rpm won't cut it. Peak torque at 1800rpm won't cut it either. Not enough HP. But peak HP does get us up there. I've towed trailers with several different vehicles and found this to be true whether it's gas at 5,000rpm in first gear or my four Cummins powered Dodges at 2600-2900rpm for the '03. Even the big rigs have to downshift to run at peak HP on the upgrade. Horsepower is not a calculation. It's a measurement of moving mass over time. How fast torque can be applied is called horsepower. The faster you can apply the most torque, the more horsepower you have. Horsepower and torque aren't two different things. 600ft/lbs of twisting force at 0 rpm is torque at 0 HP... 600ft/lbs of torque at 2900rpm is 325HP. The amount of work you can do with 600ft/lbs of torque in the Cummins 600.
Where did I claim "all engines" can do the same job?
Perhaps HID doesn't want to run at 3-5,000rpm all day to do the job his Cummins does at a more reasonable rpm and mpg. Same reason I'm not running a Hemi.
You go ahead and call DC and tell them to "loose" the Cummins and use an electric motor. That's your idea. Not mine. But the 2500 and 3500 are offered with both the Hemi and Cummins. There's a fellow on the "Open Roads Forum" towing over 10,000 with his 3500 Hemi. He sees high rpm and low fuel mileage but he's happy with it and it does the job the way he wants it. Not my bag but he didn't buy it for me.
Bottom line is, we both agree the Cummins tows better or at a far more reasonable rpm and more efficiently than a gas engine. That should be all that matters.
I don't feel torque in my truck. I feel HP. Torque is a static measurement that doesn't envolve movement. Torque being applied at increasing rpm (horsepower) is what I feel. When I'm climbing a grade, Peak torque at 1400rpm won't cut it. Peak torque at 1800rpm won't cut it either. Not enough HP. But peak HP does get us up there. I've towed trailers with several different vehicles and found this to be true whether it's gas at 5,000rpm in first gear or my four Cummins powered Dodges at 2600-2900rpm for the '03. Even the big rigs have to downshift to run at peak HP on the upgrade. Horsepower is not a calculation. It's a measurement of moving mass over time. How fast torque can be applied is called horsepower. The faster you can apply the most torque, the more horsepower you have. Horsepower and torque aren't two different things. 600ft/lbs of twisting force at 0 rpm is torque at 0 HP... 600ft/lbs of torque at 2900rpm is 325HP. The amount of work you can do with 600ft/lbs of torque in the Cummins 600.
Where did I claim "all engines" can do the same job?
Perhaps HID doesn't want to run at 3-5,000rpm all day to do the job his Cummins does at a more reasonable rpm and mpg. Same reason I'm not running a Hemi.
You go ahead and call DC and tell them to "loose" the Cummins and use an electric motor. That's your idea. Not mine. But the 2500 and 3500 are offered with both the Hemi and Cummins. There's a fellow on the "Open Roads Forum" towing over 10,000 with his 3500 Hemi. He sees high rpm and low fuel mileage but he's happy with it and it does the job the way he wants it. Not my bag but he didn't buy it for me.
Bottom line is, we both agree the Cummins tows better or at a far more reasonable rpm and more efficiently than a gas engine. That should be all that matters.
11-10-2004, 08:27 PM
#36
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Originally posted by supr
For what it is worth, beyond the HP/Torque/Calculus Doctoral thesis, I think 2000 rpm is a fairly good medium to give some boost & HP, as well as decent fuel economy. Our rigis about 36', 13-14k & 12' high, also a mileage factor. We get 11-12. If towing flat ground or nearly so, 1800 RPM works OK if I am not in a hurry. As your speed & RPM's go up. so does fuel comsumtion. You might try 2000 RPM to see if you get better speed & mileage, vs gearing down to 5th. We have 4.10's, which are perfect for Heavy loads & 55-60 mph. At 2000, you may only occasionally need 5th for hills, not too bad, maybe.
For what it is worth, beyond the HP/Torque/Calculus Doctoral thesis, I think 2000 rpm is a fairly good medium to give some boost & HP, as well as decent fuel economy. Our rigis about 36', 13-14k & 12' high, also a mileage factor. We get 11-12. If towing flat ground or nearly so, 1800 RPM works OK if I am not in a hurry. As your speed & RPM's go up. so does fuel comsumtion. You might try 2000 RPM to see if you get better speed & mileage, vs gearing down to 5th. We have 4.10's, which are perfect for Heavy loads & 55-60 mph. At 2000, you may only occasionally need 5th for hills, not too bad, maybe.
I have posted before, if I am running out of fuel and afraid of running 0ut, I drop to direct, set at about 2200 or 2300 and pick up two or three mpg. On mine that is somewhere near 52 or 53 mph.
11-10-2004, 11:06 PM
#37
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Originally posted by Hannibal
Yep. That's what I said. I don't feel torque in my truck. I feel HP. Torque is a static measurement that doesn't envolve movement. Horsepower is not a calculation. It's a measurement of moving mass over time.
Yep. That's what I said. I don't feel torque in my truck. I feel HP. Torque is a static measurement that doesn't envolve movement. Horsepower is not a calculation. It's a measurement of moving mass over time.
Bottom line is, we both agree the Cummins tows better or at a far more reasonable rpm and more efficiently than a gas engine. That should be all that matters.
11-11-2004, 08:34 AM
#38
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If you start by asking how much torque you'll need to move a 70k lb 18 wheeler up a 6% grade at 50mph, you'll be met with XXX HP and then torque will have to be calculated. It goes either way. A dyno measures HP (rate of acceleration) and torque is calculated using HP and rpm. A water brake measures torque at a certain rpm and you calculate HP from that.
I think we're both right. We just look at it from different ends of the calculation. I'm heading out to Mississippi in the morning. As long as I have enough torque/HP to get us there I'll be happy. Now about this vibration...
Have a good one!
I think we're both right. We just look at it from different ends of the calculation. I'm heading out to Mississippi in the morning. As long as I have enough torque/HP to get us there I'll be happy. Now about this vibration...
Have a good one!
11-13-2004, 09:57 AM
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Thanks! The campground has wireless internet access! I sure could have used more torque X rpm/5252 on those long rolling hills. Only got 9.6mpg in the panhandle with a strong coldfront headwind. Running 70mph called for alot of foot to the floor with our SO 250/460. We're at about 2225rpm at 70 with the 4.10. If we had a 3.73 ratio I could downshift and apply that torque 31% faster and use gear reduction to multiply torque for more power.
460 X .69 (O/D) X 4.10 = 1301 ft/lbs of torque to the rear axle.
460 X 1 (direct) X 3.73 = 1716 ft/lbs of torque to the rear axle.
Of course I would be running higher rpm but with the 4.10 I can't downshift above 60mph. The Cummins is out of breath.
70mph X 4.10 X 336/30"= 3214rpm
70mph X 3.73 X 336/30"= 2924rpm
This is the advantage of the 3.73. You might have to downshift a bit more but you CAN downshift if you need to.
I could simply run along at 55mph, save fuel, reduce noise and grow old on I-10 on the way to Mississippi... NOT!
460 X .69 (O/D) X 4.10 = 1301 ft/lbs of torque to the rear axle.
460 X 1 (direct) X 3.73 = 1716 ft/lbs of torque to the rear axle.
Of course I would be running higher rpm but with the 4.10 I can't downshift above 60mph. The Cummins is out of breath.
70mph X 4.10 X 336/30"= 3214rpm
70mph X 3.73 X 336/30"= 2924rpm
This is the advantage of the 3.73. You might have to downshift a bit more but you CAN downshift if you need to.
I could simply run along at 55mph, save fuel, reduce noise and grow old on I-10 on the way to Mississippi... NOT!
11-13-2004, 01:34 PM
#41
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You guy's wear me out!
I like my 12v loafing along with 18k in tow, just like Haulin likes his 24v loafin along making him money.
Oh Yeah, just because I like to stir the pot, horsepower doesn't mean a thing to me. Torque is what keeps my rig rollin' on.
That's why the tractors we sell have lots of gears, low horsepower, medium torque, pulling a huge load. You've got to gear the power (torque) to do the job you're trying to do.
Chris
BTW, Please don't make me get out my Physics book, I already passed that class once, I thought I'd never use any of that "knowledge" 
I like my 12v loafing along with 18k in tow, just like Haulin likes his 24v loafin along making him money.
Oh Yeah, just because I like to stir the pot, horsepower doesn't mean a thing to me. Torque is what keeps my rig rollin' on.
That's why the tractors we sell have lots of gears, low horsepower, medium torque, pulling a huge load. You've got to gear the power (torque) to do the job you're trying to do.
Chris
BTW, Please don't make me get out my Physics book, I already passed that class once, I thought I'd never use any of that "knowledge"
11-14-2004, 01:29 AM
#42
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Originally posted by Haulin_in_Dixie
Supr, I want to add this. I don't think it is the rpm that isw the big deal (within reason) but selecting a gear that does not tax the throttle too much.
I have posted before, if I am running out of fuel and afraid of running 0ut, I drop to direct, set at about 2200 or 2300 and pick up two or three mpg. On mine that is somewhere near 52 or 53 mph.
Supr, I want to add this. I don't think it is the rpm that isw the big deal (within reason) but selecting a gear that does not tax the throttle too much.
I have posted before, if I am running out of fuel and afraid of running 0ut, I drop to direct, set at about 2200 or 2300 and pick up two or three mpg. On mine that is somewhere near 52 or 53 mph.
Now you got me thinking. Opps, sorry to get of topic. Well this sorta pertains.
11-14-2004, 04:30 AM
#43
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Driving RPMs
radshooter
It looks like everybody went way off topic to me. I just finished a 2700 mile trip from Nevada to Washington state. Some real good grades to climb. I have an auto and started out without OD engaged. After about 400 miles at about 65mph and 2600rpm, I thought why am I running without overdrive so I kicked it in. 65 mph at about 1800rpm on the flats. The engine towed the 5ver along real good. When I came to a climb, I kicked it out of OD and was at the same speed (65mph) at about 2600rpm. I had no problem driving like that. When I came to a big grade and dropped down to about 40mph I put it down to 2nd gear and kicked up the rpm back to 2600. Bottom line, the Cummins will do the work for you with ease. I felt very good driving at 2600rpm which gave me about 9mpg average.
By the way, I'm towing a 40' Teton 5th wheel trailer, with triple axles. I'm not sure of the weight because I haven't weighted it yet but I'm sure it's up there with yours. ( I'll post some pictures) This was my first long trip since I got the outfit. I bought the truck to fit the trailer for retirement. Have a good time hauling. See you on the road.
It looks like everybody went way off topic to me. I just finished a 2700 mile trip from Nevada to Washington state. Some real good grades to climb. I have an auto and started out without OD engaged. After about 400 miles at about 65mph and 2600rpm, I thought why am I running without overdrive so I kicked it in. 65 mph at about 1800rpm on the flats. The engine towed the 5ver along real good. When I came to a climb, I kicked it out of OD and was at the same speed (65mph) at about 2600rpm. I had no problem driving like that. When I came to a big grade and dropped down to about 40mph I put it down to 2nd gear and kicked up the rpm back to 2600. Bottom line, the Cummins will do the work for you with ease. I felt very good driving at 2600rpm which gave me about 9mpg average.
By the way, I'm towing a 40' Teton 5th wheel trailer, with triple axles. I'm not sure of the weight because I haven't weighted it yet but I'm sure it's up there with yours. ( I'll post some pictures) This was my first long trip since I got the outfit. I bought the truck to fit the trailer for retirement. Have a good time hauling. See you on the road.
11-14-2004, 04:52 AM
#44
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Thanks LRod.
I haven't minded the off-topic twist this took. I actually learned some stuff from it. You've got to admit though, some of these folks get rather....ummm....passionate about the subject of torque/HP.
A big thanks to everyone who chimed in.
Thanks
I haven't minded the off-topic twist this took. I actually learned some stuff from it. You've got to admit though, some of these folks get rather....ummm....passionate about the subject of torque/HP.
A big thanks to everyone who chimed in.
Thanks
11-14-2004, 11:09 PM
#45
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Originally posted by radshooter
Thanks LRod.
I haven't minded the off-topic twist this took. I actually learned some stuff from it. You've got to admit though, some of these folks get rather....ummm....passionate about the subject of torque/HP.
A big thanks to everyone who chimed in.
Thanks
Thanks LRod.
I haven't minded the off-topic twist this took. I actually learned some stuff from it. You've got to admit though, some of these folks get rather....ummm....passionate about the subject of torque/HP.
A big thanks to everyone who chimed in.
Thanks
By the way I do tow around 2200-2300 rpm just fine. I will hit 2500-2800 rpm though while passing or just getting away from annoying trucks but I dont hold at that for long since I'm sure it kills mpg. Although I do read of guys that tow around those rpms for long periods. And I'm to understand the Cummins will endure max rpms all day.