Competition Ever see a 1000hp truck spooling up?

[banshee]

With all due respect, I must disagree. Torque and force are two different things. Force is measured as pounds. Torque is the multiplication of force through distance. Work is the measure of force causing displacement. Yes, I did confuse torque and work.



Take a 2000# dragster that contains 200# of fuel. Power it with a jet engine that produces 2200# of rearward force that diminishes to 2000# of force at the end of the dragstrip matching the rate at which fuel is consumed. The dragster will have constant acceleration down the track. However, since no RPM was needed to drive the wheels, there is no HP involved. For that matter, there is no torque involved, either. There is only force involved, because only force is required to displace an object, only force is required to perform work.



Now fit the dragster with gears and a rotating shaft to turn the wheels; the gears have 1:1 ratio, and the tires have 1 foot radius. Assume the dragster weighs 2000# now. Assume that the vehicle is attached to something behind it, so that 2000# of force can be applied to the shaft before launch, and once the 2000# is reached, the tether is released. To achieve the same forward acceleration as with the jet engine, you must apply 2000# of force at the interface between the tires and the pavement. This 2000# of force can be achieved by applying 2000# 1 foot from the rotating shaft, 1000# 2 feet from the shaft, or 4000# 6" from the shaft. (We ignore any losses in the drive train for this example. ) The force applied has been multiplied through distance.



In both cases, at the end of the quarter mile, the 2000# vehicle has been displaced 1320 feet - work has been performed. In the first case, HP was not involved, because a rotating engine was not driving the wheels. In the second case, HP could be measured only after the vehicle started moving (remembering that HP=Tq*RPM/5252: at 0 RPM, HP=0).



So it is not HP that moves a vehicle. It is force. And it is possible to use mechanical advantage (torque) to multiply force.

You really seem to be confusing yourself at first, but later on you're saying it right.



First of all, in your example of the thrust powered dragster you are making a completely incorrect assumption that ZERO horsepower pushed that car down the track. I'm sorry, but that's wrong. You can apply force to an object and it not move (go push against a brick wall), but once you move it you have done work, and the rate at which you complete that work is called power. Simple enough? So, in this case, a force is generated by the engine... thrust. It moves the car down the track (does work on it), and the faster it went the more power it took (more force over less time). There are ways to derive equivalent HP from a jet's thrust... it doesn't come from a spinning shaft only.



You go on to say that it's not HP that moves a vehicle, but force. I completely agree, and that's what I said from the beginning. Torque at the wheels is the important measurement to make to determine how fast your vehicle will accelerate at a given instant in time. The same calculations can be made for braking... torque at the wheels determines max braking performance (other dymanics aside). It's important to remember, though, that races don't take place in an instant... . they take TIME!!! When you apply the time element to the measurement of rear wheel torque you get... ... ... . HORSEPOWER!! The force and velocity can be interchanged to rate of output at the rear wheels. With 300hp, for example, you can either have high rpm, low torque, and high gearing (gasser) or you can have low rpm, lower gearing, and high torque (diesel). Either way, you still have 300 HP and will still get up a hill at the same speed under steady state conditions. The diesel will just last longer, get better mileage, be more driveable, and so on. This power/RPM/HP analogy is really no more different than a teeter totter with a skinny kid on one side and a fat kid on the other. You know the skinny kid has to sit farther away to balance out (more RPM if you will... weight is torque).



John

 

[Sled Puller]

With 300hp, for example, you can either have high rpm, low torque, and high gearing (gasser) or you can have low rpm, lower gearing, and high torque (diesel). Either way, you still have 300 HP and will still get up a hill at the same speed under steady state conditions. The diesel will just last longer, get better mileage, be more driveable, and so on. This power/RPM/HP analogy is really no more different than a teeter totter with a skinny kid on one side and a fat kid on the other. You know the skinny kid has to sit farther away to balance out (more RPM if you will... weight is torque).



John

Now this is where real life steps in and gives all your facts and figures a kick in the tail.

On paper, it SHOULD work like that.

But the Cummins performs better in a 300 HP level than a gasser,with 300 HP, hands down.

So, is it the extra torque, or does the Cummins just have a sweet spot, that blows the mathematics curve?

 

[banshee]

Gene,



The max attainable speed is theoretically the same... HP is HP. The diesel performs better in the real world because of its flat torque curve and that equalizer otherwise known as a turbocharger. I believe it was already mentioned, but that is also responsible for the reason why diesels will generally spin at the end of a pull and the gassers won't.

 

[Sled Puller]

HOLD IT!!

Don't throw the turbo in there, and skew your math!!

HP is HP, and TQ can be made up with gears, that is your stance, now you want to throw in another factor.



You can't have it both ways, irregardless, of number of cylinders, turbos, stroke, etc, 300 HP is 300 HP.



One is built for TORQUE.

One is not.

Which would you rather drive?



Go ahead and turbo and stroke the gasser, and watch the TORQUE come up.

 

[GIT-R-DONE]

Thanks Sleddy

 

[COMP461]

HP is HP and both being the same , both would be equal in performance . but a diesel running at half the rpms magnifies everything by two , torque , and the width of power band.



Example , bare with me on the numbers of a middle of the road diesel sled puller . I’m just using these to get a point across.



Example 1 diesel motor 800 hp rpm range say 2500 to 4200 sweet spot 2800 to 3500 Since the RPM’s are basically half of a gas motor the gearing would be half ,this doubles the amount of time the motor spends at a given RPM range requiring les numbers of gears



Example 2 gas motor 800 hp rpm range say 5500 to7500 sweet spot 6200 to 6700





Now you can see the diesel can pull for almost 3 times the amount of a gas motor with out changing gears . that said you do a turbo motor with the same power as a diesel in a gas motor ,the rpm band get wider also,



In drag racing this all changes , because you only run the motor for a short period of time and you can gear accordingly. The diesel has a big disadvantage because of the limited gears available , the only way around this is to rev a diesel up , in sled pulling the number of gears required to keep a gas motor in the power band would be excessive .



A few years back I dynoed a turbo ford motor for another race team , they were far away from home and just needed a dyno to work out a few bugs before a race . This motor was a 380 inch ford , the insides were nothing special just good durable parts . Now for any of you that don’t thank a gas motor will make torque ,this one would change you mins , it made 1897 hp and 1500 ft lbs of torque . the owner would drive it around the pits , with out towing . like a street car , it was a rock solid motor and would had made a great sled pull motor .

 

[banshee]

HOLD IT!!

Don't throw the turbo in there, and skew your math!!

HP is HP, and TQ can be made up with gears, that is your stance, now you want to throw in another factor.

What other factor are you talking about? I only mentioned the turbocharger because it is the main driver of the long, flat torque curve our diesel engines enjoy. Engineers strive to develop gas engines that have flat torque curves like we do. Like comp mentioned, it is that flat curve that makes gearing less of an issue than gas powered vehicles. Furthermore, a main reason why an equally powered gas powered truck truck will underform a diesel counterpart is gearing. Most gassers have a limited "sweet spot", and most 4/5/6 speed trannys leave gaps in the powerband. . especially when towing. Make more sense?



John

 

[Big P]

Now this is where real life steps in and gives all your facts and figures a kick in the tail.

On paper, it SHOULD work like that.

But the Cummins performs better in a 300 HP level than a gasser,with 300 HP, hands down.

So, is it the extra torque, or does the Cummins just have a sweet spot, that blows the mathematics curve?

I'm sure someone will correct me if i'm wrong but, i believe this is pretty accurate. Torque is the measure of the amount of work an engine can do, while horsepower is the rate at which it can do it. Torque is responsible for maintaining speed while horsepower is responsible for acceleration.

 

[JoshPeters]

I'm sure someone will correct me if i'm wrong but, i believe this is pretty accurate. Torque is the measure of the amount of work an engine can do, while horsepower is the rate at which it can do it. Torque is responsible for maintaining speed while horsepower is responsible for acceleration.

Now I think THAT is the best explination of Torque vs Horsepower I've seen yet!



Josh

 

[COMP461]

Torque is the amounts of force a motor can exert at a snap shot in time, meaning it can produce 500 ft lbs of torque. Hp is the total amount of work that the engine is doing, Hp remains the only constant.



Example a motor making 500 hp at 2626 rpms is making 1000 ft lbs or toque ,put that in to a 2 to 1 gear reduction , with no parasitic losses , and you have a shaft turning at 1313 rpm’s with the same 500 hp but 2000 ft lbs of torque . Now over drive it instead with a 1 to 2 overdrive gear you now have a shaft turning 5252 rpm’s making the same 500 hp and 500 ft lbs of torque.

 

[MCummings]

Just remember another thing for me.



The turbo charger keeps your motor (Diesel or otherwise), at 300RWHP when you are on the beach, or at the top of Pikes peak. Naturally Aspirated motors don't have that advantage. That 345HP (flywheel) Dodge HEMI will be weezing at the top of Pikes hill. You might be lucky to get 250RWHP out of it. Your turbo motor will still be pumping, and supplying the air for 300RWHP.



Down here 300HP Gasser out run the 300HP Diesel's because they are in 2nd gear at 60MPH, when I'm in 4th. Their gear multiplication HP is awesome. They are spinning 4,500RPM making 400RWHP, while I'm stuck at 2,000RPM, putting down 300RWHP.



Both of our motors are making 300HP, but because they are using a bigger prybar (gear multiplication), they are able to put down more RWHP.



Merrick

 

[jetenginedoctor]

The turbo charger keeps your motor (Diesel or otherwise), at 300RWHP when you are on the beach, or at the top of Pikes peak. Naturally Aspirated motors don't have that advantage. That 345HP (flywheel) Dodge HEMI will be weezing at the top of Pikes hill. You might be lucky to get 250RWHP out of it. Your turbo motor will still be pumping, and supplying the air for 300RWHP.

Merrick, you're not quite right when you state that the 300hp turbo diesel will make the same power regardless of elevation.



While it's true that they don't lose power as badly as an NA engine, increase in elevation/altitude means the turbo has to work that much harder to build enough upper deck pressure (CDP) and open the wastegate at the desired pressure. This means added drive pressure thus increased exhaust restriction, and spinning the compressor harder trying to impart a higher pressure ratio on the inlet charge as determined by the wastegate spring, boost controler, etc. The harder the turbo has to work, the more of a restriction it becomes, and net HP available at the crank goes down.



No engine, not even a turbocharged diesel, is immune from the effect of decreased air density as a result of increase in elevation, air temp, or humidity.

Down here 300HP Gasser out run the 300HP Diesel's because they are in 2nd gear at 60MPH, when I'm in 4th. Their gear multiplication HP is awesome. They are spinning 4,500RPM making 400RWHP, while I'm stuck at 2,000RPM, putting down 300RWHP.

There is no such thing as gear multiplication HP. You can multiply torque and tractive effort with gears, not HP. A 300HP gasoline engine can only make that much power. . . . 300HP.

Both of our motors are making 300HP, but because they are using a bigger prybar (gear multiplication), they are able to put down more RWHP.

Nope. You cannot change HP with gears, only torque and tractive effort.





BK

 

[MCummings]

I'll give up on this one.



I know that more HP and TQ is good, and I don't consider myself too bad on getting more HP from the diesels.



I'll just stick to telling people 100 more HP and 180TQ, and leave the differences between HP and TQ out of it.





I guess I could even go against myself, and say that there is less RWHP in lower gears since the drivetrain is not accelerating as fast as it would in direct, or O. D.



Maybe that's why the diesels do so well in O. D. on the dyno?



I think I will forever have cranial rectum inversion on this subject.



Merrick

 

[AndrewKing]

The way I had it explained to me as to why a Diesel engine is better for towing (HP for HP vs a gas engine) is that Gas engines have Rising Torque (That is Torque increases as RPMs increase to a point of course). Whereas truck Diesels (and alot of equipment diesel engines like bull dozers and tractors etc)... have Torque Rise (that is as load increases and RPMs decrease, diesels will very often hunker down and actually develop even MORE torque... again of course to a point). This distinction or diffence is importnat because when pulling a load up a steep hill a gasser will often have to gear down to keep the load moving... . Of course if the gasser runs out of gearing, and the RPMs continue drop... . its basically ball game over for the gasser because torque decreases as RPMs decreases... In all fairness tho the gasser can keep a load moving but would have to find a gear low enough to allow the engine to have enough rpms to have enough torque to keep things moving. In contrast, a diesel will generally be able to hunker down and keep rolling (most HD diesels will give figures for torque rise as a percentage)..... of course within reason. . Note: While Power Strokes are diesel engines they have torque curves more like a gasser (rising torque), while Cummins engines have Torque rise.

Another reason a 300 HP diesel is better than a 300 HP Ricer is the rpm at which the power is generated... . while 300 HP is 300 HP, a small highly tuned engine would require insane RPMs to reach the 300 HP where as 300 HP in a Diesel occurs at a more usable RPM (imagine having to slip a clutch at 6500 RPM to try to get a load moving (of course you'd have to do it ohhh sooo slowly because remember gassers are torque rise motors... . let the clutch out too fast and the gasser runs out of its torque. . Fast... . Of course slipping clutch for the time needed for a 4 banger to move a heavily loaded vehicle would quickly result in a fried clutch (yes you could argue that you could use lower gears for the gasser (and yes you would need it) BUT you'd need soo many gears it would really not be practical (of course nobody really tows seriously w/ a ricer but It was just provided as a more extreme example to make the point)..... The above is how somebody explained Torque Vs HP and Gas VS diesel to me..... Hope this helps and makes sense.



Andrew

 

[BigEasy]

think about it this way... .



bigger HP AND bigger TQ numbers are better. Who wants to debate that?

 

[COMP461]

how about lets all settle this Bigger is better . Well most of the time , well some of the time. Something is always better then nothing :-{} :-{} :-{} :-{} :-{} :-{} Oo.

 

[jwilliams3]

Happy Thanksgiving!!!

 

[JLackman]

Excellent discussion.



I joined TDR just to post to this thread.



HP can be directly measured. Simply insert a spring scale in the hitch of a horse drawn plow, crack the whip, note pounds, time, and distance and run the numbers. If the scale reads 550 pounds for one foot of movement in one second's time - it’s one HP. Drawbar HP readings probably evolved out of this initial method of directly measuring HP. (This might be why the inline scales like Dillon, Chatillon, etc are still called dynamometers) The steam engine invented by James Watt exposed problems in measuring HP directly. Since they produced rotary motion, not inline motion, their flywheel HP could not be directly measured with the normal time/pounds/distance formula. Measuring drawbar HP directly was easy but didn’t include wasted HP such as slip and machine friction. Any true GearHead wants to know flywheel HP. But these engines performed work too fast to measure their flywheel HP directly. Yes it could be done, by clutching the engine’s flywheel to a drum and lifting a weight, like a winch, recording speed, etc. What a mess that would be especially because a true GearHead knew these engines would become more and more powerful. So grandfather Gear Head (let’s have a moment of silence please), I don’t know if it was Watt, came up with the idea of measuring flywheel Torque and RPM directly and then calculating HP. Early absorbers were probably brakes on a drum with a torque arm acting on a spring scale used much the same manner as the power absorbers of today. Modern water brake, eddy current etc. power absorbers allow practically unlimited “slip” while still retaining the ability to hold an engine’s full torque at wide open throttle. (During a WOT dyno test the absorber controls the engine RPM. )



In a running and loaded IC engine HP and TQ are practically the same thing. Saying things like (and I've said them too) "torque gets you off the line HP gets you down the track" mean nothing. All modern engine dynos directly measure rotary TQ and RPM and calculate HP. Constant load chassis dynos directly measure rotary TQ and RPM and calculate HP. I don’t know how the Nebraska Tractor Testing drawbar HP ratings were measured but they may have been or still are direct HP measurements, which brings me to my closing idea. Why not build a load cell in the hitches of the pulling sleds and directly measure the HP of the pullers rigs? It would be fairly easy to program a PC knowing pounds (from the load cell) time and distance. Wouldn’t that be kind of cool?

 

[jwilliams3]

Jesse,

Nice equipment and website, good read too!

 

[Sled Puller]

Excellent discussion.



I joined TDR just to post to this thread.





GLAD TO HAVE YOU!



. I don’t know how the Nebraska Tractor Testing drawbar HP ratings were measured but they may have been or still are direct HP measurements, which brings me to my closing idea. Why not build a load cell in the hitches of the pulling sleds and directly measure the HP of the pullers rigs? It would be fairly easy to program a PC knowing pounds (from the load cell) time and distance. Wouldn’t that be kind of cool?

Thats actually been discussed, And yes, it would be cool as hell!!



I have always said, I wanted to know the power my truck was making hooked to a sled, not on a dyno.