Is Torque a canstant value?

[Sticks]

Is the torque output of our engines a constant, or can it be specifically targeted for increases?



At the last Dyno day that we had, I noticed a couple of trucks putting down 500+hp and 1030+torque, then saw another truck roll up and throw down mid 400 HP and near 1100 torque. Kind of a noticeable difference going on here.



With each engine design that is out there (12v, 24v 24vSO 24vHO 24v03) we can bolt on stuff to increase the HP, and the torque follows. Is that a constant curve for the torque to follow the HP or are some mods more prone to a higher percentage of torque increases?



Example



Injectors 100 hp and 150 tq



Fueling box 100 hp and 200tq



(These numbers are not actual, I am hoping to show an example of two products that add the same HP but different TQ)

 

[NPloysa]

Good Question

You know, Sticks, I was just about to ask the same thing. I have been thinking about this for a while too, mostly to myself and then kind of forgot about it.



If you look at most diesel engines in the big 3, rated torque is approximately double the rated horsepower.



Like you mentioned, at the dyno day most of the guys' trucks were putting down approximately twice the torque of their horsepower.



Then you have the exception, like the 400/1100 guy that you talked about, where 550 and 1100 or 400/800 would be more like it...



I hope someone can answer!

 

[fest3er]

HP = Torque * (RPM / 5252)

Thus, if your engine produced constant torque (say, 1000 lb-ft), HP would increase linearly,
from 152 HP at 800 RPM, through 323 HP at 1700 RPM, to 608 HP at 3200 RPM. It would even reach 1140 HP at 6000 RPM (which a few 6Bs are known to run at).

No, torque is not constant. When you increase fuel and air input into the engine, you are actually increasing torque (the force of the piston pushing down on the crankshaft). HP is achieved through time. That is, at any specific point in time, a piston could generate a certain amount of torque on the crank. But time must pass before any HP is generated.

Look at the torque curves the dyno produces. You'll see the torque rise, hold kind-of steady, then fall off again. And you'll see HP do something similar, but HP will also be dependent on RPM.

Fest3er

 

[SRadke]

If a truck were to start out strong through the rpm range and then fall on it's face for lack of turbo or any other reason it would have a high torque number and not so high HP right? I imagine a fueling box could be programmed to do just that but I don't see a reason why you would want to.



-Scott

 

[marksmith]

Hmmmm mid 400's and 1100 tq sounds like me at PDR dyno day. I had 439. 4/1110 I dyno'd four hours later for three hp less and about 30 ft-lbs less. I dunno but I tell you I am having a heck of a time keeping a clutch under me. I spin an OFE at will on 5x5. And this is my SECOND one. It might be because my truck is a 'flier' or maybe a custom rezonator that I havent finished getting all the numbers for. Dunno but when I get a for sure answer I will be sure to tell all.



Take care

Mark

 

[Sticks]

OK, so given that hp will follow the torque, what can one do to specifically increase torque?



I know the big rigs are close to three to one (tq - hp). Are our little engines capable of say 1100tq @ 350hp?

 

[WadePatton]

Omigosh, the TQ and HP again.

I'm no engineer, but my butt is often seen poking out from under a Dodge hood.



I believe that the 2-2. 5 x HP = TQ equation for our engines is pretty much a factor of the 5. 9 design/displacement. I don't think you're going to change that ratio very much.



That being said, some of our engines appear to be "torqier" than others.



Engine timing may be the biggest factor as to which way your engine leans. You can play with that more on the 12v.



Mine 24v leans to the torque side. I think I'll make 1000TQ before I get to 500HP.



On "our" dyno, the two most similar stock trucks I've seen run was mine and Jay's. Jay's made 10-15 more HP and mine made 15-20 more TQ. It'll be interesting to see if, as he BOMBs his, if that trend continues.

 

[Steve St.Laurent]

sticks - as fest explained that's a function of rpm. The reason you have numbers like that on a big rig is because they are governed at much lower rpm's. Look at the numbers that fest gave for hp and torque given an engine that produces 1000 ft/lbs across the board. You can see that if an engine was governed at say 2100 rpm versus 3200 rpm that it would have a much higher tq to hp ratio - but only because the hp is lower because of the lower rpm. In actuality most engines do not produce an absolutely linear torque output across the board so that complicates things for comparisons purpose. The bottom line is that torque is a better indicator of how much power an engine makes and horsepower is a mathematical calculation that takes acceleration capability into account. ie - you CAN have 1000 ft/lbs of torque being produced and not be moving anywhere - therefore no horsepower.

 

[jgillott]

Here is a link that is directly related to the discussion. Hope it helps. Sorry if you have already been there.



http://www.howstuffworks.com/question381.htm



Justin