The mysteries of Horsepower and other things explained

[Turtle_n_Peeps]

There seems to be a lot of confusion about the mysteries of engines by some on this site so I will post some links and add some text to try and clear some of this up.

First some terms:

Torque: A twisting force.

Horsepower: A unit of power equal to 550 foot-pounds per second (745.7 watts). The power of an engine measured in terms of this.

Duty cycle : The cycle of operation of a machine or other device that operates intermittently rather than continuously.


Since torque is simply a measurement of a twisting force one can't determine how much work is being done from just that term. I could say I am applying 1000 ft/lbs of force on a pipe wrench and if the joint doesn't break loose I’m not doing any work and that would be 0 HP. If the joint breaks loose and I can swing that pipe wrench 10 RPM's then math tells us I'm producing 1.9 HP.

Now; same situation: Someone tells me they can produce 1.9 HP. Since HP is a timed base formula I know they are doing work unlike if I just have a torque number. What I don't know is if they are making a lot of torque with very little RPM (Ex- 1000 ft/lbs of torque and 10 RPM = 1.9 HP) or if they are producing little torque (Ex- 10 ft/lbs of torque and 1000 RPM = 1.9 HP) or anything in between. As one can see, we have the EXACT same amount of work produced whether I have a lot of torque or not.

In the above example, if one has a contest between the two, math will show us the result will be a dead even tie.


It's simple to make torque or more torque:
One thing that a lot of people don't understand is that anybody can double or triple or whatever the amount of torque they want to make to their wheels if they have enough gears.
EX: If I have 100 HP and have 500 ft/lbs of torque to my wheels with a 5 to 1 final drive and want to double torque output all I have to do is double the final drive gear to 10 to 1 and now I have 1000 ft/lbs of torque to my wheels. Unfortunately, I still only have 100 HP but I have twice the torque value to my wheels. I will still only be able to climb a hill at X speed because; remember; I still only have 100 HP. (Remember, I'm not doing any more work or making anymore HP because HP is a timed based formula, all I'm doing is changing the amount of torque that gets to the wheels to keep the engine at its best operating curve.)

You can't change power with a gear change.
Remember that timed based formula? It proves by math that a gear change can't make more HP. (Ex: if we can lift 100 lbs of weight with a 2 to 1 gear and do it in 1 minute of time it will take twice as long to lift 200 lbs of weight with a 4 to 1 gear. Again, HP is the same. (the math says it has to be.)

The more HP an engine has the less gear you need:
This is a hard concept for some to grasp. I have seen time after time after time people on here say it's stupid for manufactures to only offer a high gear ratio for their diesel trucks. They don't understand that gears are nothing more than a round lever. (Ex: A big strong guy may need a very short lever to lift 500 lbs (tall gear) where a weak guy will need a very long lever to lift 500 lbs (short gear). (In the above ex, the strong guy will be making more HP even though the weak guy can still lift the load but will take longer doing it)

Now where a short gear will help is with duty cycle. Remember, even the big guy will get tired and if he has a long lever, he will be able to work longer and with less effort. (It will also take longer to do his work with a longer lever)


Duty cycle goes down as HP goes up.
Two different engines with the same HP can have WAAAAAY different duty cycles.
EX: My 2006 Duramax has 360 HP. The 3.5 Ecoboost has 365 HP. On a hot day my Dmax has a WAAAAAAY higher duty cycle than the Ecoboost. It all has to do with how an engine is designed. It has nothing to do with it's a gasoline or diesel engine thing. Diesels "usually" have a higher duty cycle although there are industrial gasoline engines out there that have extremely high duty cycles compared to a light duty diesel pickup engine. Again, it's a design thing and not a diesel/gas thing.


A truck has a 3.00 rear end and you change the gear set out to a 4.56 rear end. Which gear set will make more HP to the ground?
The answer is the 3.00 will make more power (slightly). Yes I know it's splitting hairs and yes I know; that doesn't seem right, but it is. Remember, torque does not make HP and the shorter the gear the more friction and loses it has hence the "slight loss" in HP.


Engine 1, a turbo diesel puts out 200 HP and 420 ft/lbs of torque; engine 2, a gas puts out 345 HP and 375 ft/lbs of torque. Which one will be first to the top of the hill in a towing contest.

All being equal (weight, sea level etc) who will win a towing race up a hill?
The HP formula teaches us it won't even be close. The gasoline engine will smoke the turbo diesel up the hill in the above example. But what about all of that big torque the diesel is putting out? Remember, torque is not power and never will be!
(These are true numbers from my 6.5 turbo diesel and a 5.7 Hemi)

An Ecoboost has 365 HP and a Dmax has 360 HP; who will win a towing race up a hill?
The HP formula says it will be a very close race at the end, even though my Dmax has a ton more torque than the Ecoboost. In all likelihood the Dmax will win the race even though the Ecoboost has slightly more HP.
"But wait; you said above that HP always wins; I told you torque was King!!" Sorry but that is not the reason the Ecoboost will lose the tow up the hill.

The reason is, HP curve. It takes time for an engine to build up RPM and since a diesel takes less time to get to peak HP it will be quicker off of the line "so to speak." Like I said, it will be close though because of the HP equality.


So what does all of this mean?
Lets wrap this whole thing up.

Number one on the list is: Torque alone is not power or work and never will be.

Torque plus RPM IS power and work. We have another name for it. It's called Horsepower and it can tell you how much work is being done in how much time!

You can't make HP with gears; you can only make more torque and torque is not power.

The shorter gear you have the (higher numerically) less HP you will get to the rear wheels. Again, this is splitting hairs because the amount is very small but it is true.

Just because it's a diesel doesn't mean it's more powerful.

Just because it's a gas engine does not mean it can’t be faster up a hill than a diesel with a lot more torque.


Here is some good reading to back up some of the statements made:
Really good reading about engine myths.

nmReally good reading from CAT about RV's and HP. (notice CAT doesn't even talk about torque)

Gears and HP to the ground.

[4x4ord]

Hannibal wrote:

4x4ord wrote:

Kind of..... Saying "higher HP puts more torque to the drive wheels and pulls the grade faster." is not really accurate because HP needs to be geared to do what your asking of it. If a 500 HP tractor is capable of putting 600,000 lb ft of torque to the rear axle in low gear but has a top speed of 20 mph it obviously isn't going to be much of a match against a 396 HP Duramax towing a 10,000 lb RV up a 6% grade.

Or if you are comparing two fairly similar pickups to each other, such as was the case when Pickuptrucks.com faced off the Ford against the Duramax and Ram. The lower horsepower and lower torque Duramax pulled its trailer up the Eisenhower pass and sat and waited for nearly 2 minutes for the F350 to finally catch up. there was all sorts of speculation as to why...things like Ford's turbo couldn't spin fast enough at the high altitude of the test (and that could have played a role) but GM conducted the test; The goal was to exploit Ford's weaknesses so if high altitude was going to exploit the turbo let's pick the Eisenhower pass. Then the GM engineers looked at the gear ratios on that new Ford 6r140 and noticed how it is programed to be kind of lazy. The 6r140 will not downshift from 4th to 3rd until the engine rpm drops below 1900 rpm. They knew the slope of the hill they would choose, all they had to do was select a weight for the trucks to hook on to that would pull that poor little Ford down to just above 1900 rpm and it would struggle up the hill in 4th gear where that mighty new 400 HP Powerstroke was only producing 280 HP.

Anyway if you want a simple statement to make regarding horsepower you might be able to get away with saying something like; "Given the right gears Horsepower trumps Torque every time" But going by the actual definition of the words Horsepower and Torque are measuring entirely different things.

I think we're agreeing on the subject. Just coming at it from different angles. Peak HP numbers matter but you have to have gears matched to the engine to allow it to reach peak HP at the speed you want it too. I like the 3.73 rear gears with gas or diesel as it put my Cummins Rams just under peak hp on the grades at 60mph in direct and the gas V8 just under it's peak hp in 2nd or third with the Torqshift 5spd. I'm sure the new transmissions change everything but it still has to be geared to match the engine's power band at the speed you intend to run. Otherwise you'll be lacking horsepower.
For whatever reasons the Ford wasn't able to produce the necessary hp to run with the GM, it was still horsepower that it was lacking. That was pretty clever of GM to calculate a way to exploit the Ford's weakness. My 5.4L F250 is a little on the lazy side too. In tow/haul mode, full throttle launch will shift to the next gear at around 4400rpm rather than it's 5k rpm peak hp. Still enough hp for our lightweight 5th wheel.
I don't discount torque at all. It's the measure of an engine's strength. Higher torque means more hp at lower rpm and usually a stronger built engine overall with the exception of one that only uses 4 bolts per cylinder in it's heads. A high torque, low hp engine will likely be as strong as an ox. And just about as fast.

We are definitely on the same page. I guess I should say that my story about the GM engineers is only that....a story. I would like to call it my theory but in reality it's just my guess.

[Hannibal]

transamz9 wrote:

You guys could always get yourself an old Willys Jeep.......

Willys

Gotta love the old sleepers. :C

https://www.youtube.com/watch?v=zHcJaLqcf_4

[Hannibal]

4x4ord wrote:

Kind of..... Saying "higher HP puts more torque to the drive wheels and pulls the grade faster." is not really accurate because HP needs to be geared to do what your asking of it. If a 500 HP tractor is capable of putting 600,000 lb ft of torque to the rear axle in low gear but has a top speed of 20 mph it obviously isn't going to be much of a match against a 396 HP Duramax towing a 10,000 lb RV up a 6% grade.

Or if you are comparing two fairly similar pickups to each other, such as was the case when Pickuptrucks.com faced off the Ford against the Duramax and Ram. The lower horsepower and lower torque Duramax pulled its trailer up the Eisenhower pass and sat and waited for nearly 2 minutes for the F350 to finally catch up. there was all sorts of speculation as to why...things like Ford's turbo couldn't spin fast enough at the high altitude of the test (and that could have played a role) but GM conducted the test; The goal was to exploit Ford's weaknesses so if high altitude was going to exploit the turbo let's pick the Eisenhower pass. Then the GM engineers looked at the gear ratios on that new Ford 6r140 and noticed how it is programed to be kind of lazy. The 6r140 will not downshift from 4th to 3rd until the engine rpm drops below 1900 rpm. They knew the slope of the hill they would choose, all they had to do was select a weight for the trucks to hook on to that would pull that poor little Ford down to just above 1900 rpm and it would struggle up the hill in 4th gear where that mighty new 400 HP Powerstroke was only producing 280 HP.

Anyway if you want a simple statement to make regarding horsepower you might be able to get away with saying something like; "Given the right gears Horsepower trumps Torque every time" But going by the actual definition of the words Horsepower and Torque are measuring entirely different things.

I think we're agreeing on the subject. Just coming at it from different angles. Peak HP numbers matter but you have to have gears matched to the engine to allow it to reach peak HP at the speed you want it too. I like the 3.73 rear gears with gas or diesel as it put my Cummins Rams just under peak hp on the grades at 60mph in direct and the gas V8 just under it's peak hp in 2nd or third with the Torqshift 5spd. I'm sure the new transmissions change everything but it still has to be geared to match the engine's power band at the speed you intend to run. Otherwise you'll be lacking horsepower.
For whatever reasons the Ford wasn't able to produce the necessary hp to run with the GM, it was still horsepower that it was lacking. That was pretty clever of GM to calculate a way to exploit the Ford's weakness. My 5.4L F250 is a little on the lazy side too. In tow/haul mode, full throttle launch will shift to the next gear at around 4400rpm rather than it's 5k rpm peak hp. Still enough hp for our lightweight 5th wheel.
I don't discount torque at all. It's the measure of an engine's strength. Higher torque means more hp at lower rpm and usually a stronger built engine overall with the exception of one that only uses 4 bolts per cylinder in it's heads. A high torque, low hp engine will likely be as strong as an ox. And just about as fast.

[BenK]

Built a Willys when 15, but poor and just back to stock with my meager paper boy,
mowing lawns, etc income

My dune buggy would have given this kid a run for it

Yes, wheel base on both of mine too short for the kinds of speeds this kid
seems to run up to. Plus too high a CG and the biggie...too high of an air gap
to pavement to allow air down there to lift the vehicle.

Back to the topic and comment on duty cycle

It is all about heat. Generation (spot area/size, rate of generation, etc) and
rejection management.

If you can reject the heat fast enough and keep it within design temps (best at
the low end), then you can have the power allowed thermally

Then the limiting factors will no longer be thermal, but mechanical strength
of the weakest link

Like the example of a DC electric motor's ability to have over 100% torque at ZERO
RPM...it's duty cycle will drop like a rock. Depends on the heat rejection characteristics
of the motor's rotor construction. As the stator has the motor casing as a heat
sink

[Bedlam]

transamz9 wrote:
You guys could always get yourself an old Willys Jeep.......

Willys

That's way too short a wheelbase for such an swap and not including a ROPS.

[transamz9]

NC Hauler wrote:

4x4ord wrote:

NC Hauler wrote:
^^^^^THAT WAS AWESOME!!!!!..Over 200 mph, AGAINST the wind.!!!!....^^^





:B

Awesome? Maybe.....I think it's nuts. There are idiots like me who lack the common sense and self discipline to keep that power bottled up. So far so good, I have resisted any temptation to look at anything but an SUV for our next car.

That makes two of us, thus the reason I'll never own one, (other than price:))..I couldn't resist the temptation to run just about anything that would be on the road...I never grew up and am one of those idiots myself....ask my wife:B

You guys could always get yourself an old Willys Jeep.......

Willys

[NC_Hauler]

4x4ord wrote:

NC Hauler wrote:
^^^^^THAT WAS AWESOME!!!!!..Over 200 mph, AGAINST the wind.!!!!....^^^





:B

Awesome? Maybe.....I think it's nuts. There are idiots like me who lack the common sense and self discipline to keep that power bottled up. So far so good, I have resisted any temptation to look at anything but an SUV for our next car.

That makes two of us, thus the reason I'll never own one, (other than price:))..I couldn't resist the temptation to run just about anything that would be on the road...I never grew up and am one of those idiots myself....ask my wife:B

[4x4ord]

NC Hauler wrote:
^^^^^THAT WAS AWESOME!!!!!..Over 200 mph, AGAINST the wind.!!!!....^^^





:B

Awesome? Maybe.....I think it's nuts. There are idiots like me who lack the common sense and self discipline to keep that power bottled up. So far so good, I have resisted any temptation to look at anything but an SUV for our next car.

[NC_Hauler]

^^^^^THAT WAS AWESOME!!!!!..Over 200 mph, AGAINST the wind.!!!!....^^^





:B

[transamz9]

NC Hauler wrote:

transamz9 wrote:

NC Hauler wrote:

transamz9 wrote:

Bedlam wrote:
An even bigger difference is in the Hemi 6.4 gasoline engine based on application:

Challenger - 485 hp with 475 ft lbs
Pickup - 410 hp with 429 ft lbs
Chassis Cab - 367 hp with 429 ft lbs

I'm pretty sure everyone would love to but their foot to the floor of the Challenger and leave it there...

LOL! It would definitely be fun........until you had to make a curve.


We have an '06 F550 with 4.88's that stays hooked to our Goose neck and when you drive it loaded it's foot to the floor on the interstate. Now this is with a .71 OD instead of .6X in the Aisin. I believe our F550 tops out at 83. LOL!

I'd prefer to put my foot to the floor in a Dodge Challenger SRT Hellcat, at 707HP and 650lb-ft of TQ..it would be fun, AND I understand the suspension is up to taking corners at a faster speed than one might think:)

.........and it would literally blow the doors off anything mentioned above:B

Well.....blowing the doors off is a little far fetched.......I mean the doors are mounted pretty solid on the before mentioned vehicles.:B

OK, so I embellished:B

Would still like to take that bad boy for a ride:)

For your dreaming pleasures....

Hellcat Foot Through the throttle body

[4x4ord]

Hannibal wrote:

4x4ord wrote:

Hannibal wrote:

4x4ord wrote:

Hannibal wrote:

shepstone wrote:
I don't quite understand why max hp and max tq are both achieved at different rpm ? and with that which of the 2 rpm's should I be using to get the most out of an engine when climbing or accelerating with a heavy load?

Max horsepower will put the most torque to the rear wheels.

It kind of depends how you look at this question. Say you start climbing a hill with a big trailer. As the grade increases you floor it and your transmission drops two gears and the engine is running at near the rpm where it makes maximum power. The hill is long and getting steeper, you keep your foot to the floor but the engine continues to loose rpm; as it slows it continues to increase the torque to the rear wheels until it either meets the demand of the hill or the rpm drops to where the e.engine is making maximum torque. If the hill still demands more torque another downsjit is required and the engine increases its rpm again so it can start the cycle over again. Anyway you will pull the hill the fastest in the gear that keeps your engine revved close to the rpm where maximum HP is achieved but in each gear the rpm where the engine makes the most torque is always the rpm where the engine will pull the hardest in that gear.

True. However, if I'm rolling along at 65mph in my '03 Cummins powered Ram with it's flat torque curve in O/D at 2k rpm towing our 5th wheel and along comes a 3% hill that's too steep to maintain speed in O/D, if I let it downshift to direct to run 2800rpm, I can increase torque to the rear axle from 1301ft/lbs to 1886ft/lbs and maintain speed. Same 460ft/lbs of flywheel torque but I went from 175hp to 245hp.
With my 5.4L F250, downshifts are common. With it's less flat torque curve, it might make less flywheel torque at 3k rpm or 5k rpm than at it's 3800rpm peak but through gear reduction/torque multiplication, I'll be putting much more torque to the rear axle at 4500rpm than at 3800rpm running the same road speed. More HP means more torque to the rear wheels.

I basically agree with what you're saying. Like you described for the Ram, here is a hypothetical scenario using some real numbers for a Ford. Obviously there are details ommitted; like driveline inefficiencies and wind redistance to keep it simple.

Say a Ford 1 ton hits a steep hill pulling a trailer at 64 mph. The weight of the truck/trailer and slope of the hill determine that a torque of 3431 lb ft is necessary on the rear axle to pull the load up the hill. You push your foot to the floor and the transmission downshifts two gears. At this point the engine is revving 2900 rpm, your in 4th gear and still traveling 64 mph. At 2900 rpm the Powerstroke makes its maximum power of 400 horsepower. So it is making 400 x 5252/2900 = 724 lb ft of torque at the crankshaft. Multiplying this through the 4th gear ratio of 1.15:1 and the final drive ratio of 3.73 we can calculate the torque on the rear axle to be 3107 lb ft. The truck starts to slow down. Now if you chose to manually select 4th gear so the transmission could not downshift, the engine would continue to slow down all the way to 1700 rpm where the Powetstroke makes its maximum torque value of 800 lb ft. At that point the required rear axle torque to get the trailer up the hill of 3431 is just met. So you would be able to pull the load up the hill in 4th gear at 1700 engine rpm (which is the engines maximum torque rpm) at a speed of 37 mph.

So now back up to where the truck begins slowing down from 64 mph. As soon as the engine rpm drops to 2194 rpm you manually shift the transmission to 3rd gear. The engine revs to 2900 rpm and you are going 48 mph. At this engine rpm the crankshaft torque is 724 lb ft. Running that torque through the third gear ratio of 1.52 and the rear axle ratio of 3.73 the engine and transmission are able to deliver 4100 lb ft of torque. The truck would start to accelerate up the hill in 3rd gear until the crankshaft torque drops to 605 lb ft of torque. We can only guess the rpm the engine could rev to.... maybe 3200 rpm and 53 mph.

So running in 4th gear at max torque you could climb the hill at 37 mph and in 3rd gear revving the engine high you could pull the hill at about 53 mph.

Which goes back to higher HP puts more torque to the drive wheels and pulls the grade faster. I saw this many times with my Cummins powered Rams. I like this video of a 6.7L PSD towing 13k? lbs up a long grade. Far more realistic than so many claims made here. I saw 2900rpm a lot with my last two Cummins powered Rams. Peak horsepower numbers do matter when you find yourself maxed out on a grade.

https://www.youtube.com/watch?v=-_1ZefREs0Y

Kind of..... Saying "higher HP puts more torque to the drive wheels and pulls the grade faster." is not really accurate because HP needs to be geared to do what your asking of it. If a 500 HP tractor is capable of putting 600,000 lb ft of torque to the rear axle in low gear but has a top speed of 20 mph it obviously isn't going to be much of a match against a 396 HP Duramax towing a 10,000 lb RV up a 6% grade.

Or if you are comparing two fairly similar pickups to each other, such as was the case when Pickuptrucks.com faced off the Ford against the Duramax and Ram. The lower horsepower and lower torque Duramax pulled its trailer up the Eisenhower pass and sat and waited for nearly 2 minutes for the F350 to finally catch up. there was all sorts of speculation as to why...things like Ford's turbo couldn't spin fast enough at the high altitude of the test (and that could have played a role) but GM conducted the test; The goal was to exploit Ford's weaknesses so if high altitude was going to exploit the turbo let's pick the Eisenhower pass. Then the GM engineers looked at the gear ratios on that new Ford 6r140 and noticed how it is programed to be kind of lazy. The 6r140 will not downshift from 4th to 3rd until the engine rpm drops below 1900 rpm. They knew the slope of the hill they would choose, all they had to do was select a weight for the trucks to hook on to that would pull that poor little Ford down to just above 1900 rpm and it would struggle up the hill in 4th gear where that mighty new 400 HP Powerstroke was only producing 280 HP.

Anyway if you want a simple statement to make regarding horsepower you might be able to get away with saying something like; "Given the right gears Horsepower trumps Torque every time" But going by the actual definition of the words Horsepower and Torque are measuring entirely different things.

[jmckelvy]

This has been an entertaining thread with some interesting comments. 🙂

But it is also obvious that some of the posters simply don't get the difference between torque and horsepower.

BTW the OP is correct.

[transamz9]

Hannibal wrote:

4x4ord wrote:

Hannibal wrote:

4x4ord wrote:

Hannibal wrote:

shepstone wrote:
I don't quite understand why max hp and max tq are both achieved at different rpm ? and with that which of the 2 rpm's should I be using to get the most out of an engine when climbing or accelerating with a heavy load?

Max horsepower will put the most torque to the rear wheels.

It kind of depends how you look at this question. Say you start climbing a hill with a big trailer. As the grade increases you floor it and your transmission drops two gears and the engine is running at near the rpm where it makes maximum power. The hill is long and getting steeper, you keep your foot to the floor but the engine continues to loose rpm; as it slows it continues to increase the torque to the rear wheels until it either meets the demand of the hill or the rpm drops to where the e.engine is making maximum torque. If the hill still demands more torque another downsjit is required and the engine increases its rpm again so it can start the cycle over again. Anyway you will pull the hill the fastest in the gear that keeps your engine revved close to the rpm where maximum HP is achieved but in each gear the rpm where the engine makes the most torque is always the rpm where the engine will pull the hardest in that gear.

True. However, if I'm rolling along at 65mph in my '03 Cummins powered Ram with it's flat torque curve in O/D at 2k rpm towing our 5th wheel and along comes a 3% hill that's too steep to maintain speed in O/D, if I let it downshift to direct to run 2800rpm, I can increase torque to the rear axle from 1301ft/lbs to 1886ft/lbs and maintain speed. Same 460ft/lbs of flywheel torque but I went from 175hp to 245hp.
With my 5.4L F250, downshifts are common. With it's less flat torque curve, it might make less flywheel torque at 3k rpm or 5k rpm than at it's 3800rpm peak but through gear reduction/torque multiplication, I'll be putting much more torque to the rear axle at 4500rpm than at 3800rpm running the same road speed. More HP means more torque to the rear wheels.

I basically agree with what you're saying. Like you described for the Ram, here is a hypothetical scenario using some real numbers for a Ford. Obviously there are details ommitted; like driveline inefficiencies and wind redistance to keep it simple.

Say a Ford 1 ton hits a steep hill pulling a trailer at 64 mph. The weight of the truck/trailer and slope of the hill determine that a torque of 3431 lb ft is necessary on the rear axle to pull the load up the hill. You push your foot to the floor and the transmission downshifts two gears. At this point the engine is revving 2900 rpm, your in 4th gear and still traveling 64 mph. At 2900 rpm the Powerstroke makes its maximum power of 400 horsepower. So it is making 400 x 5252/2900 = 724 lb ft of torque at the crankshaft. Multiplying this through the 4th gear ratio of 1.15:1 and the final drive ratio of 3.73 we can calculate the torque on the rear axle to be 3107 lb ft. The truck starts to slow down. Now if you chose to manually select 4th gear so the transmission could not downshift, the engine would continue to slow down all the way to 1700 rpm where the Powetstroke makes its maximum torque value of 800 lb ft. At that point the required rear axle torque to get the trailer up the hill of 3431 is just met. So you would be able to pull the load up the hill in 4th gear at 1700 engine rpm (which is the engines maximum torque rpm) at a speed of 37 mph.

So now back up to where the truck begins slowing down from 64 mph. As soon as the engine rpm drops to 2194 rpm you manually shift the transmission to 3rd gear. The engine revs to 2900 rpm and you are going 48 mph. At this engine rpm the crankshaft torque is 724 lb ft. Running that torque through the third gear ratio of 1.52 and the rear axle ratio of 3.73 the engine and transmission are able to deliver 4100 lb ft of torque. The truck would start to accelerate up the hill in 3rd gear until the crankshaft torque drops to 605 lb ft of torque. We can only guess the rpm the engine could rev to.... maybe 3200 rpm and 53 mph.

So running in 4th gear at max torque you could climb the hill at 37 mph and in 3rd gear revving the engine high you could pull the hill at about 53 mph.

Which goes back to higher HP puts more torque to the drive wheels and pulls the grade faster. I saw this many times with my Cummins powered Rams. I like this video of a 6.7L PSD towing 13k? lbs up a long grade. Far more realistic than so many claims made here. I saw 2900rpm a lot with my last two Cummins powered Rams. Peak horsepower numbers do matter when you find yourself maxed out on a grade.

https://www.youtube.com/watch?v=-_1ZefREs0Y

What claims are you referring to that's not realistic?

[v10superduty]

4x4ord wrote:

v10superduty wrote:
OK, I have read this thread on and off for several days.
Its way to deep and hurts my head.. :W

Can someone just tell me "yes or no" please?

Can I go back and reread the OP original post and take that info to the bank? Its correct or no?

Will sure make things easier.. :B

Basically yes. I read if over quickly and noticed three things that I didn't think were quite right.

1st: Turtle says:
The more HP an engine has the less gear you need:

Although I understand what Turtle is getting at the fact is that gearing has much more to do with the power band of an engine, rpm and application than it has to do with a peak HP figure.

2nd: Turtle says:
A truck has a 3.00 rear end and you change the gear set out to a 4.56 rear end. Which gear set will make more HP to the ground?

Turtle explains that he is splitting hairs here and he is. I believe that, although Turtle's explanation is true and there is application for this, it would have been better off not to mention as it could lead to more confusion then what could be gained.

3rd: Turtle says:
Torque plus RPM IS power and work. We have another name for it. It's called Horsepower and it can tell you how much work is being done in how much time!

The way Turtle stated this is wrong. It should be stated

Torque X RPM = Power... Torque X RPM/5252 = Horsepower

Power doesn't necessarily involve torque and rpm. Power is as Turtle said in the onset of his post, the rate of doing work. Power can also be thought of as force applied at a velocity or work per time. So: force X distance/time = Power.... lbs x ft/(33000 minutes)= Horsepower

Somewhere in this thread I noticed someone posted a link to a Hot Rod Articaal explaining horsepower. I didn't open the link but if its the article I am thinking it likely is, then that is one of the best write ups on Horsepower that I have read.

Well I think this thread should be made into a sticky and the next time someone posts
"I am thinking of buying a new tow vehicle, what brand should I buy, do you think it will pull a ____________ "
They are told they must read this entire thread first.. :B :B :B :B

That'll teach them to troll like that.. :@