Horse Power

Here we go again. I don't want to get into another long debate. I will just say to research this more, you sound as if you believe that HP and torque are two indipendant and different things. They are not, they are directly related and really the same thing (torque is just lacking a timeframe to measure work). Torque is force, HP is torque over time (work).

 

Whatever, you believe what you want, and I'll believe what I want. That's the good thing, we can each think differently. Just as an experiement, turn your 600 HP 1850 torque engine down to 600 HP and 1350 torque, then get back to me with the results. Do some real world testing like I have with different torque ratings but same HP settings.

 

I have done real world testing with a lot of dyno time under my belt as well. Torque is meaningless without rpm, so where is peak torque on those engines, lets say 1300 rpm.

1350 ft-lbs at 1300 rpm = 334.16 HP.
1850 ft-lbs at 1300 rpm = 457.92 HP.

These are facts, you cannot change them. In your own example, the higher torque engine pulls better because it as over 120 more HORSEPOWER.

Now, lest say 600 peak HP is at 1800 rpm on both engines. 600 HP at 1800 rpm = 1750 ft-lbs. To limit torque to 1350 and still get 600 HP, you have to rev it over 2300 rpm.

This was my whole point, you do not understand the relationship between the HP and torque and need to get called out when you post nonsense. Give me some more examples and will show you that the more powerful engine has more horsepower. The math is quite simple. Believe what you want, but I suggest that you open your mind and educate yourself on the subject so that what you believe is correct. I have no doubt that you drove with 1850-ft lbs and 1350 and that the 1850 out pulled the 1350, but you don't understand why?

 

If torque doesn't matter, and HP is the end all, then why do manufacturers offer multiple torque ratings with the same HP?

Example:

http://cumminsengines.com/isx15-heavy-duty-truck-2013#ratings

 

You have to look at the power curves. I never said that torque does not matter, I said that it's meaningless without RPM. RPM gives you the time frame and torque over time is horsepower. Multiple peak toque figures are there for different applications, mainly a lower peak torque would be used if the driveline was not rated for the higher torque rating. This is the same reason that some engines reduce toque in lower gears. But anyway, here's the math on the ISX 600.

Both engines have 600 HP, it doesn't give rpm, but it'll be around 1800 for peak HP, so we know both engines have 1750 ft-lbs at 1800 rpm. Both engines have peak toque at 1200.

The 2050 ft-lb engine has 468.39 HP at 1200 rpm.
The 1850 ft-lb engine has 422.7 HP at 1200 rpm.

I'm pretty sure that we both agree that the 2050 ft-lb engine will pull better. It pulls better because it has more HP at lower rpm, which makes more average HP throughout the RPM range. Torque can be multiplied through gearing, HP cannot. You can trade speed for pulling power or vice versa, but you cannot trade off anything through gearing to gain HP. There is more to it that peak #'s. To get a good comparison, you really need to look at the dyno graphs. I was not disagreeing with you about higher toque engines pulling better, that is true many times, but not all. I was disagreeing with your explanation of it.

Lets think about smaller simpler numbers to simplify it a bit. 2 engines with 500 ft-lbs peak torque. Engine A's peak torque is at 1000 rpm. Engine B's is at 2000 rpm. If we did not know RPM, both engines sound equal. But engine B can pull the same load at twice the speed, so it has double the HP. You can trade speed for torque by gearing engine B to 1000 rpm, which will double the torque. So now engine B is geared to the same speed as engine A, but now has 1000 ft-lbs. So it can do twice as much work at the same speed as engine A.

On the flip side, a 500 hp is 500 hp, it doesn't matter what rpm. A 500 HP engine at 2000 rpm will do the same work as a 500 HP engine at 8000 rpm. Geared to the same axle speed, they will have the same toque at the axle.

 

This is math - my strong suit - when discussing what will go up a hill faster there is only one correct answer. I probably wouldn't be able to turn down that much and maintain 600 hp, but it could be done. If I kept it at the 600 hp rpm there would be zero difference.

 

Different power curves, also to much driveline requirements. More torque requires heavier driveshafts, differentials, etc..

 

This is the epitome of the discussion, you can never compensate for lack of HP, but you can for torque with more gearing. If we had zero loss through the driveline, you would always put the exact same amount of horsepower at the wheels that you're producing at the crank, but the torque would be multiplied. 4:1 multiplication gives you 4x torque at 1/4 the speed.

If two engines are making the same horsepower, but engine A is making twice the torque at half the speed (it has to be the same multiples due to how horsepower is calculated) but has half the gearing, engine B is making half the torque at twice the RPM with twice the gearing, both engines will pull exactly the same at that road speed. The torque at the wheels is the same. Too many people confuse torque at the engine with torque at the wheels. Gearing needs to always be considered, and total gearing (Tranny X axle) not just rear gear.

 

....my mind is blown and I'm struggling to put it back together....

 

I'm talking real work, not theories, math, running on a dyno, ect. You put two trucks with 500 hp, .73 od trans, 3.55 rears and 1800 rpm limit pulling 45 k up a hill. The 500hp truck with 1650 torque will reach the top much faster with less gear changes than the 500hp with 1450 torque. That can not be disputed if anyone has ever driven a truck with low torque ratings.

Yes, gearing can change anything. That's why the 1450 torque truck would have to drop two gears and the 1650 wouldn't have to drop any on the same hill.