What is the optimum RPM range for towing up hills. Do I want to keep my RPMs at a level where my vehicle is producing peak torque? My 5.7 GM makes peak torque at 2,800 RPM's. Does that mean I want to keep it at 2,800 RPM's on hill/mountains? It seems a lot of people with gas engines will report towing in the 4,000+ RPM range when climbing steep hills. Don't you lose torque when you go above the peak torque RPM's?
I'm guessing, That those turning 4000+ RPM are trying to go too fast up the mountain. My TV turns 2900 at 45 mph in 2nd gear goihng up the mountsin. It will go faster, and turn more RPM. but 3000 RPM is all I want to turn. Mines makes all it's power from 2500 to 3000. See no need to rev higher. I don't mind going up at 45 mph.
2800 to 3800 is good. Much more and you will be looking at an upshift and much less and you are looking at a downshift. You can run it up 4500 if you think it will pull the next gear because you may need 2800 rpm after the shift in order to pull with the next gear. I will often set the cruise control at 3500 rpm locked in 2nd or even low gear and just cruise to the top. Now if we had eight speed transmissions and geared to where we could use overdrive you could choose the rpm much better. But we don't so it is often a compromise and you have to adjust your speed down to match a good rpm.
2001 F150 SuperCrew 5.4 Lariat Offroad 4x4 Tow Package 4.10 Truetrac
2006 Keystone Springdale 249FWBHLS
12K SuperGlide, KGE3000Ti 2.3kw rated 2.6kw max
Frank's voltage booster, Prosine 1800 powered by 4 GC2 batteries
mrad wrote: What is the optimum RPM range for towing up hills. Do I want to keep my RPMs at a level where my vehicle is producing peak torque? My 5.7 GM makes peak torque at 2,800 RPM's. Does that mean I want to keep it at 2,800 RPM's on hill/mountains?
The short answer is yes, I would think you want to maintain your engine near it's peak torque output in demanding situations.
From Edmunds.com article on Torque:
Quote: ....at low speeds the transmission's gears work to transmit maximum torque from the engine to the wheels. You want this because it takes more force, or torque, to move a vehicle that is at rest than it does to move a vehicle in motion (Newton's 1st Law). At the same time, once a vehicle is underway, you want less torque and more horsepower to maintain a high speed.
Torque overcomes resistive forces (i.e. wind, gravity wanting to pull your trailer back down hill ) while horsepower keeps you moving at a certain speed.
The equation is: HP= Torque * RPM / 5252
mrad wrote: Don't you lose torque when you go above the peak torque RPM's?
Yes, both torque and horsepower have curves that peak at a certain RPM and then fall off. The chart below from GearVendors.com shows the torque curve for an L31, Votec5700 engine.
You can see the curve is sort of flat up to about 3,200RPM but really falls off after that. Basically, the leverage your truck has against the load declines after 2,800RPM. So, to make the load move faster, the engine has to turn faster to compensate for decline in torque output. In a hill situation, you want the truck applying it's maximum force on the load.
Look at the chart LIKE2BUILD posted. Sorry I could not get it to display
It takes horsepower to get up the hill. If you keep the engine at peak torque that is where you will use the least fuel. But with this example you will only have about 175 horsepower. You will be forced to go slower than if you up your rpm to 4600 rpm where you will have about 265 horsepower. At 4600 you will go up the hill faster but use more fuel and put more strain on the engine.
The people that push their engines to 4000 and beyond are in a hurry and do not care about how much fuel they are using. I have always been uneasy about taking any American made large V8 beyond 4000.
Depends on the engine. According to the chart like2build posted, there would be little point in running your engine much over peak torque, I generally aim for somewhere between peak HP and peak torque. Looks like about 3500 rpm for your truck. The only answer is to know your engine. My Trailblazer had an inline 6 with "90% of peak torque is available from 1600 rpm to 5600 rpm", the torque curve was as flat as the Dmax I have now. Peak HP was at 6000 rpm, so pretty much anywhere between 2000 and 6000 rpm was game.........that was a great towing engine. I had a 3/4 ton with the 6.0 gas, used to run it around 4500 rpm. The Dmax peak torque is at 1800 rpm, but peak HP is 3200 rpm.......I sure dont loaf along at 1800 rpm up a hill. Guess Im one of the people who dont worry about the fuel bill, I could afford the 300+ HP so I dont care about saving .50 cents climbing a hill.
mrad wrote: What is the optimum RPM range for towing up hills. Do I want to keep my RPMs at a level where my vehicle is producing peak torque? My 5.7 GM makes peak torque at 2,800 RPM's. Does that mean I want to keep it at 2,800 RPM's on hill/mountains?
The short answer is yes, I would think you want to maintain your engine near it's peak torque output in demanding situations.
From Edmunds.com article on Torque:
Quote: ....at low speeds the transmission's gears work to transmit maximum torque from the engine to the wheels. You want this because it takes more force, or torque, to move a vehicle that is at rest than it does to move a vehicle in motion (Newton's 1st Law). At the same time, once a vehicle is underway, you want less torque and more horsepower to maintain a high speed.
Torque overcomes resistive forces (i.e. wind, gravity wanting to pull your trailer back down hill ) while horsepower keeps you moving at a certain speed.
The equation is: HP= Torque * RPM / 5252
mrad wrote: Don't you lose torque when you go above the peak torque RPM's?
Yes, both torque and horsepower have curves that peak at a certain RPM and then fall off. The chart below from GearVendors.com shows the torque curve for an L31, Votec5700 engine.
You can see the curve is sort of flat up to about 3,200RPM but really falls off after that. Basically, the leverage your truck has against the load declines after 2,800RPM. So, to make the load move faster, the engine has to turn faster to compensate for decline in torque output. In a hill situation, you want the truck applying it's maximum force on the load.
KJ
Boy I'm glad someone actually posted the TQ/HP curves for a gasser. For those graphs I would shoot for around 4000 to 4500 for best towing performance and then adjust based on performance for your combo. The biggest advantage of the diesel is the torque peaks and drops off much less vs. the HP and a diesel you wind it up and let it scream since that's what they are made for. My diesel max torque is around 2K rpms and when pulling hard I will wind it up to 3K to 3.2K (redline is like 3.5 or 3.6K).
Larry
2001 standard box 7.3L E-350 PSD Van with 4.10 rear and 2007 Holiday Rambler Aluma-Lite 8306S Been RV'ing since 1974. TRAILER MODS
That's why I chose the 3.73 ratio in my truck. At 60mph up a steep one in 2nd gear, my engine is turning right at it's 375ft/lb peak torque 4200rpm with power to spare. 2nd gear's 1.67 ratio multiplies that 375ft/lbs to 626ft/lbs at the output shaft of the transmission. Plenty for pulling the grades. Of course you have to take into account the loss of 3% for every 1k ft of elevation with a NA gasser and power take off's like a/c, power steering and the transmission itself. It does fine and 4200rpm won't hurt a thing. On the interstate, I set cruise at 65mph and let it do it's thing. An occasional 4500rpm, 900rpm below peak hp and 2300~rpm below the stock 5.7L Hemi's limit~, won't hurt it either. If you're afraid to let your engine run in it's powerband when power is needed, you'll never realize the power your engine really has. And you'll never realize how much torque multiplication does for towing heavy with a SB gasser. On the flats to mild interstate rolling hills, we run 2700~rpm in direct.
'05 2500HD Dodge 5.7L Hemi 5spd auto/3.73 SLT. 95k miles
ex '95 Cummins,'98 12v Cummins,'01.5 Cummins,'03 Cummins
'07 KZ Jag 28JFSS.
Hannibal wrote: That's why I chose the 3.73 ratio in my truck. At 60mph up a steep one in 2nd gear, my engine is turning right at it's 375ft/lb peak torque 4200rpm with power to spare. 2nd gear's 1.67 ratio multiplies that 375ft/lbs to 626ft/lbs at the output shaft of the transmission. Plenty for pulling the grades. Of course you have to take into account the loss of 3% for every 1k ft of elevation with a NA gasser and power take off's like a/c, power steering and the transmission itself. It does fine and 4200rpm won't hurt a thing. On the interstate, I set cruise at 65mph and let it do it's thing. An occasional 4500rpm, 900rpm below peak hp and 2300~rpm below the stock 5.7L Hemi's limit~, won't hurt it either. If you're afraid to let your engine run in it's powerband when power is needed, you'll never realize the power your engine really has. And you'll never realize how much torque multiplication does for towing heavy with a SB gasser. On the flats to mild interstate rolling hills, we run 2700~rpm in direct.
Exactly. Never have understood why people brag about their engine only "needing" to turn ~2K (diesel) or ~3K (gas). If youre only going to use 150 HP why pay for the bigger engines?
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) while horsepower keeps you moving at a certain speed.
