Not sure if it's been discussed here before, since I'm somewhat of a new member, but one trend I keep seeing (especially since the new 6.7 intro) is that everyone keeps refering to horse power as the end all of truck engine ratings. I'm not ranting here but guys and gals please take a look at the following info. HP is just a function of Torque and really doesn't mean anything. Torque (given the right number of gears to select from) is what is important.

Torque is the moment of a force, acting at a distance (which tends to cause rotation).

Work, in a linear since, is the product of a force exerted on an object and the distance that object moves. With spinning objects (think input shaft here) work is defined as the product of torque causing a rotation and the angle through which the object turns.

Power is work done in a certain time unit.

So:

power=work/time or (torque*angular rotation)/time

Horsepower=(Torque*RPM)/5252 (this is why you see HP and Torque lines crossing at 5252RPM on dyno sheets, if you have an engine that revs that high)

The new 6.7 as I understand it is a 5.9 with a longer stroke. When going from shorter stroke to a longer stroke actual piston speed being dependent on a larger circumference crank rotation is higher (speed of the piston is faster at given points of crank rotation) which translates to the need for much higher rates of acceleration and de-acceleration at the end of the stroke for the piston travel. This is why (usually anyway) that engines that have been stroked have lower max RPM ratings and hince lower HP ratings for a given torque value.

Sure, I would have liked to see a higher torque rating for the new 6.7 but given that fact that the first intro for the new 6.7 is for commercial duty cab chasis trucks and the fact that these new trucks will have egr's, cat's and particle filters it's not that bad. Something else to keep in mind. I would bet that the torque curve for the 6.7 is much flatter and keeps a higher rating at extended RPM's than the 5.9 does. Just a guess but is usually the case for longer stroked engines.

Sorry for the long post.

 

Uhhhh.....okay. Can you please explain the theory of relativity?

The way I see it, torque is for hauling horsey's, and horsepower is for haulin booty.

 

While your physics are inarguably correct.....I diagree with the statement of hp not being important. Since hp is a number that represents the relationship of torque and time (in this case, time = RPM), hp is telling us at what speed we can apply that torque. It takes much more energy to deliver 600 ft/lbs of torque at 3000 rpm than to deliver 600 ft/lbs at 1500 rpm and the number that represents that difference is hp.

The hp curve can tell us a lot about how an engine will perform.

I'll take the engine that makes 350 hp with 600 ft/lbs over the engine that makes 300 hp and 600 ft/lbs all day long because without seeing that actual power curves of the engine, I know the 350 hp egine has a broader range of torque....and it is the curve not the peak # that is much more important.

I don't want an engine that makes huge torque at 1500 rpm but can't carry a significant amount of it's peak torque past it's peak torque rpm.....this scenario will show up in an engine that makes low hp and will perform poorly. While I do want as much torque as soon as possible, I don't want it at the sacrifice of a poor torque curve that has a small rpm range of usable torque.

 

I agree and that's why I stated that I would bet that the 6.7's torque curve will be even flatter than the 5.9's. The 6.7's crank will have more angular momentum due to the large diameter. I haven't compaired many dyno sheets for the Cummins vs the DMax and PSD but I would also guess that the torque curve for the Cummins is much flatter than the competition's. This is why the Cummins/47 or 48RE has been able to keep up with the competition even though it has fewer gears (and uses a broader range of RPM to transfer work to power). In a perfect world for diesel effiency, you would have an engine that would only operate at it's ideal RPM range (max torque RPM plus a couple hundered RPM) and have enough gear selection to accomodate the speed you desire. This would give you the best senario for fuel mileage as well. It would be hard to get a 20 speed auto in our size trucks though

 

horsepower IS important... torque is a measure of work... horsepower is a measurement of how FAST you can use that work...

say you've got a big guy that can carry 5 buckets of water from the well to the fire, but it takes him 10 minutes to get to the fire and then back to the well... in 20 minutes, he can bring 10 buckets to the well...

then you've got a little guy that can carry 2 buckets at a time, but it only takes him 2 minutes to get to the fire and back to the well... in 20 minutes, he can bring 20 buckets to the well... his torque numbers are lower, but he's got more horsepower

everyone always brags on the torque of these trucks... they're always going to make a LOT of torque... too much in some instances... I focus on horsepower, the torque will follow. I'd MUCH rather have 600hp and 900ftlbs of torque (I know, that ain't gonna happen) than 400hp and 1200ftlbs. the 600hp truck will be easier on parts and will be faster down the track. and either will pull a trailer just fine! LOL!

 

Sure, quick and dirty:

If you are travelling away from a clock at the speed of light (and would somehow be able to keep seeing the clock) the dials would not appear to move therefore, time stops when travelling at the speed of light. (That's why SOL is not attainable)

 

But that's the different theory of what TRUCKS are designed for. Hauling heavy or drag racing. For a truck I'd rather be able to haul the 5 buckets and get there with all five buckets than have to make 5 trips only being able to carry 2 buckets at a time. I have a car and a couple of motorcycles for that!

 

I think this way of measuring power is flawed. A motor that revved twice as high could have half the torque and still have the same hp rating. Just doesn't seem right to me.

 

May seem flawed but it's still the case. (can't argue with physics) That's why I say that HP is not what's important. It's torque.

 

Ok I've got a question for you, on the 12 Valve trucks what can be done to increase horsepower that’s not going to increase torque proportionally? In my case I dyno’ed at 321 HP, and 812 torque, at the time I thought the HP was lower than I expected and the torque was higher. Any suggestions on how to get the HP up without bring the torque up.

 

Produce the same torque at a higher RPM and the HP will be higher.

HP = (Torque x RPM) / 5252

5252, by the way is 33,000 lb-ft/minute (the definition of 1 HP, English units) divided by 2 x Pi to convert from a linear to a rotating frame of reference.

Rusty

 

If you trace the definition of HP back to James Watt, he was trying to sell steam engines to lift water out of coal mines, a job that was then being done by draft horses. In order to establish a basis of comparison, he found that a horse could lift 550 lbs of water 1 foot in 1 second - this became the definition of 1 HP. Multiplying by 60 seconds per minute, this definition extrapolates to 33,000 lb-ft/minute = 1 HP.

Now, to try to make sense of this in terms of torque, if the horse were stronger but no faster than our 1 HP baseline horse, it could (let's say) lift 1100 lbs of water 1 foot in 1 second, thus producing 2 HP. This is a "higher torque" horse, and we've doubled the amount of water coming out of the mine each minute.

Conversely, if the horse were no stronger but faster than our 1 HP baseline horse, it could lift 550 lbs of water 1 foot in 1/2 second. In doing so, it would produce 2 HP just like the stronger horse above - although it has only half the torque of the "higher torque" horse, it's working twice as fast. This is the "higher RPM" horse, in engine terms, and it also doubles the amount of water coming out of the mine each minute as compared to our 1 HP standard of reference.

So, both 2 HP horses will do the same work per unit of time - they just differ in the way they accomplish it.

Rusty

 

HP = (Torque x RPM) / 5252 is an inarguable equation of physics.....it does not matter what kind of engine or motor is used....if it makes torque and spins at any given rpm, the hp equation applies.

HP isn't a true measurement of force (that is what torque is). It is a number that represents the relationship between torque and time (rpm).

Torque is measured and HP is calculated.

 

HP and Torque both matter; but im a torque kind of guy myself. My buddy(Teddy Bear on here) has an 03 Chevy 6.0 2500 4x4 gasser w/some mods. He dynoed something like 280hp, and i htink right around 300lb/ft torque. I havent dynoed in a while, but Id say I have at/close to 700 ft/lb of torque and probably right at, or a little shy of his HP. We are both Dead even in a drag race unloaded(unless I build boost), but with a load, I am pretty sure he couldnt do anything at all with me. HP I think is more important racing, and torque is what matters with pulling a load. HP almost always comes in at high rpm's. thats why gassers feel dead until they get some rpm's. And the torque is why a Diesel(or a cummins anyway) pulls like a freight train at 1400rpm's. If you are pulling loads you dont need much HP, just torque. If you are drag racing; HP is mainly what you need. I like a lot of Both, but my tranny doesent

Eric

 

The new 6.7 is a totally different engine than the euro 6.7. It has a bigger bore as well as different stroke. They have an article on it over at that other website.