HP vs TQ continued......


kjewer1
04-07-2004, 03:54 AM
This is a question I get asked often in PMs, so I thought I would make this a thread so everyone can see it. Perhaps I should add to the one already started, but I think when threads get long (with my ramblings) they can get overwhelming. So this will focus on a specific aspect of that thread. If the mods think it would be better in the other thread, feel free to merge them.

Hey Kevin...how are you doing?

Look that this \/

http://www.automotiveforums.com/vbulletin/showthread.php?t=162564&page=2&pp=15&highlight=questions+shifting

I'm sure you remember that...i would think you would.I need alittle help getting it.I under stand that your only feel torque.But like...you say that horsepower does everything right?But isn't hp torque?If hp is torque then why do you say that it takes hp not torque to get down the track?Lets say that i'm not moving...i have the clutch in and in first gear.I like out the clutch and push on the gas pedel.Does that mean its hp that makes me move or torque?What makes the car move?"TQ is what pulls you off the line and HP is what takes you thru the trap and the finish line"."TQ doesnt even get you off the line. HP does EVERYTHING".I dont get that.If i dont really need torque then why dont i just get a honda?If hp does everything then why do we have torque?But then hp is torque?How can this be?

I get a lot of questions on this. ;) Its all in that thread, but I will focus on that segment for a bit. You are correct in saying that HP and TQ are really the same thing, since they are mathematically linked. Its the CONCEPT of what each one is that defines what I was trying to say. TQ is simply a measure of force in a twisting motion. No movement is needed to apply toqrue. Lets say your lugnuts are at 100 ft/lbs. You put 90 ftlbs on them with a breaker bar. They wont move, but are you apllying toruqe? Of course you are. But there is no movement. So a motor that makes torque doesnt necessarily move the car :) It seems odd, becuase in the car example, torque always equals movement. Unless you foot-brake or brake-torque your auto on the line to build boost, then you will see what I mean here. So TQ doesnt not require movement.

HP is tq, but with distance and time expressed as well. Its a measure of work done, not just force applied (TQ is just a measure of force applied). If there is a force applied (tq) but now movement, is any work done? Nope. Who ever gets more work done faster will get down the track faster and in less time. You can make 10,000 foot pounds of torque, but if you dont MOVE, no work is done. Not to mention your ET will suck :D

So while TQ and HP are attached at the hip, HP is the measurement we are concerned about when talkign about the track. And that means ET and mph. None of this tq is front end hp is backend BS. The HP and TQ curves of your motor apply in every gear, not the beginning or end of the track....

For the honda example. There are plenty of hondas out there that make shyte for torque, but they still run nice ETs/MPHs. Why? At the RPM they run them at they make plenty of HP. If they made more low end torque, they would make more HP over more of the rpm band, right? This extra "area under the power curve" would lead to more work being done in each gear. Its important to note though that if you arent going to raise your rpm (and your ability to make tq at that hgher rpm), you HAVE to increase TQ to increase HP. So in this sense they are effectively the same thing.

Wether you make more tq at lower rpm, or less tq but higher rpm, the end result is a given HP. And this is why HP is important when talking about track performance. HP will express all of these variables in one figure, and express how much work is being done over time/distance, which is after all what we are doing at the track. Time, distance, and how much work we can get done.

They are the same, but different. I hope this has helped sort it out a little better. But the more I try to explain this, the more complicated it seems to get. Once you "get it" it will seem much simpler than all of these discussions. I dont know if I posted this link before, but it will explain this in another way, which may make more sense to some people. It also goes over gearing...

http://www.geocities.com/MotorCity/7177/torquehp.html

EclipseRST
04-07-2004, 04:25 AM
since you get asked this so much i am goin to sticky it until we can decide what to do with it... we should make a big thread of questions so that we can stop getting the same question asked everyother day! what do ya think?

nintendo89
04-07-2004, 06:16 AM
I have never heard of an eclipse RST, what is that?

duckydsp
04-07-2004, 09:38 AM
eclipse rst is Jake's special. Nothing else like it.

JoeWagon
04-07-2004, 06:54 PM
There is a place for questions that get asked a lot.. FAQ.

On a sidenote, Jake isn't the only person with a turbo'd RS, there are plenty. My friend's got a civic CXR (CX type R conversion).

kjewer1
04-09-2004, 02:51 AM
Here is another PM repsonse I wrote tonight on the subject. I think I finally got some of these thoughts into words in a way that might make some sense. Hope it helps.


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The key to remember is the twisting force is definitely what moves the car, but you can have a twisting force (or any other force) applied, with no motion. The formula for work is Force times Distance. So for work to be done something has to move. You can push on a building with 100 pounds of force, but you arent doing any work, since the building wont move. You may be sweating, but it doesnt mean you are doing work :) The definition of one horsepower is 33000 ftlbs of work done in one minute. So now we have distance and time in addition to our twisting force. So tq is what moves the car, but HP tells us what that tq is doing (distance covered over a period of time, aka, work). In the car sense, what it really tells us is at what point in the rpm range we are making torque, since HP is tq x rpm, divided by 5252.

TQ is hard to make. Takes displacement, airflow, etc. In many cases it is easier to increase HP by increasing rpm rather than TQ. This is the way the hondas work. Little tq, but plenty of HP. This is why they can run the same track times as big V8s that make much more tq, but at lower rpm (lower HP). And this is why HP is directly tied to track times, and not tq. My turbo diesel truck makes 600 ft lbs, but at such low rpm its only ~250 HP. A 7200 pound truck with 600 ft lbs (TONS of torque) is still no faster than a car that only makes 250 HP with only 200 ftlbs (but higher rpm). The reason is more TQ but lwo rpm can turn taller gears, and less TQ but more rpm can turn lower gears longer (before redlining), so it all equals out. In fact, in both caes with different gear ratios and different TQ output, WHP will be the same ;)

To make a car faster, sure you can make more TQ. OR, you can make the same (or a little less) TQ, but go to higher RPM and "take advantage of gearing"... The end result is the same, and you see it at the track all the time. Low TQ high reving imports running right with big TQ low reving V8s. ET and MPH depend on HP, not torque, even though TQ is the force moving the car.

Hope this helps!

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And to add a little more confusion to this, lets look one more time at the definition of HP. Just thought of another way to explain it. 33000 ftlbs per minute means that in one minute 33000 pounds moved a foot, or 1 pound moved 33000 feet, or anything in between (33 pounds moved 1000 feet, etc). Has to multpily out to 33000. So lets look at that again. 33000 ft pounds per minute. We have weight there (weight of the car), distance there (1/4 mile), and time there (your ET). So the formula for HP has everything we need to express out ET and MPH (distance over time, both included in the definition for HP above). TQ only has force and distance, nothing about time. So there is no pissible mathematical way to talk about track performance based on TQ alone. This is really the best explanation of it, though it may take a "math type" person to get it. :) Hope it helps.

JoeWagon
04-09-2004, 04:01 PM
Makes plenty of sense to me, glad to be able to say I understand it pretty clearly. :)

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