Difference between HP and Torque

[cronus1987]

This is the easiest way for me to think about it..
Take a heavy duty diesel engine for example. a 14L straight 6. it makes about 1600 ft*lbs of torque, but only makes about 500hp. That's because it doesn't rev high enough to build much HP (in comparison to it's torque ratings) but even with only 500hp it can haul 40,000lbs with no problem. Also, it makes all of that torque at very low RPM so it's got power from idle.

Take your average i-4 bike.. 40 ft*lbs of torque and 130hp. There's not much torque there, but it revs so high it builds a lot of hp. Also, it makes it's max torque number way up in the rpm range. So while you can't pull anything with it it's going to move pretty quick once you get it into it's power band...

Basically.. in the end HOW MUCH torque you have isn't near as important as WHERE you have it. This goes for whether you want a stump puller or you want an indy car. HP is really nothing more than an extrapolation of how much torque at what speed. That doesn't mean HP ratings don't matter. they do. You just need to find out why your HP rating is what it is and if that suits your application.

The reason a buell is more fun to ME is because i mainly just blast around town, commute, or hit some twisty roads, so i'm not way up in the rpm range most of the time, but my power is right there easily within reach.
An i-4 is different. you don't have that power when you take off from a redlight. You have to wait for the power to build up in the rpm range. When it does, HOLY HELL, but while you're waiting to get there...not so great.

understand?

 

[upthemaiden]

Cronus, I think your response helped a bit. That's definitely the kind of riding I'm looking to do this time around. The Triumph I had was my (fun)commuter, so rain/shine/snow/cold I was on it, but I was closer to 20 years old and didn't mind going 90+mph wherever I was going just to have access to all the power it had. Once I get back on the road I'll just be doing some calmer more laid back rides in town or on nice back roads. No real intention on ever taking it on the highway, so it definitely sounds like what I'm looking for, I've just been confused about some peoples complaints.

My other question, is where do parallel twins fit in? I had always assumed it was different from a v-twin because of the obvious sound difference between my wife's gs500 and harleys/buells, but now that I know more about the differences in stroke, I know that the noise her bike makes is more a long the lines of an sv650 or some other higher revving twin. Once I get her bike out on the street in a month or two, will that engine behave more like the xb engine, or an i-4 engine? or somewhere right in the middle since the redline is somewhere around 10k, if I remember right.

 

[bolt08]

someone please correct me if I am wrong on this, but I remember reading an article about this some time ago:

TORQUE: (if i recall correctly) when measured in foot pounds is the rotational strength to lift (?) pounds one foot away from the center point of rotation. Basically if you put a bar on your crank and went one foot out that bar, how many pounds of pressure or lift is exerted at that point. I hope that made sense [confused]

HORSE POWER: the power needed to pull 33,000 pounds one foot in one minute. (this is where the time factor comes in to play)

like I said, it's been a while since I read the article and I can't seam to remember where I read it; sorry. Anyway, I hope that my attempt at the definitions helps.

 

[TooFst]

The best I ever heard it said was hp is how fast.... more Torque gets u there quicker. Allways stuck with me. There can't be a formula can there?? I saw my buddys gixer on a dyno. He had 130hp and 62ft. lbs.

 

[upthemaiden]

There can't be a formula can there??

The formula is HP =(Torque x RPM)/5252

That's one of the few things I do know.

 

[Rebel_CafeRacer]

Torque is what gets things moving, HP keeps things moving.... just wanted to put in my 2 cents...

 

[Pockets]

git yurself a friggin Buell& the point will be moot!

+1

 

[RT Performance]

you wife twin will be have like a 4 cyl.
Rice bikes are all rev monsters producing alot higher hp than torque.
like others have said Torque is what sets you back in you seat when you mash the gas.
Hp is how fast you can get to top speed .
Why did Eric not Build a hp motor.
He probably consoderd it but he wanted an american sport bike. and when harley Bought him Back. they are the ones that kept him away from water cooled engines.
you really need water to keep a 10k plus engine alive.

 

[brightbuell]

Go test ride a buell and all your questions will be answered. So simple. In real life situations a buells power is much more accesable. Put it this way you will always beat anyone to the next stop light cause your power in instant off the line and out of the turns. Also because the power is always there you dont need to shift half as much thus you can enjoy the ride more with half the work. Its a undescrible riding EXP!

 

[upthemaiden]

Yeah, I think I've got it figured out as far as the power being accessible as opposed to all top end on an i-4.

I've heard a lot of the same stuff from plenty of different people, so the key is making it easy enough for someone to understand who doesn't have a background in engines/engineering/whatever else it takes. Maybe if I try looking at it from a completely different point of view. Tell me if this is a good comparison...
You take a 300lb body builder and put him next to a 150lb kid with a strong heart, good lungs, and some good stamina, and you put them both on a bicycle with the same tall gear ratio. The body builder can obviously stomp on the pedals and get the thing moving pretty fast, the 150lb kid is using all his weight but still takes forever to get the thing moving. Once they're going though, the body builders legs obviously aren't meant for high speed repetition, so he only gets moving 15mph and then his legs, although plenty strong enough, just aren't moving any faster. That kid now that he's moving just has those pedals and skinny legs spinning like crazy, he can get his bike moving 25mph because moving that fast is nothing for his legs/lungs/heart. Even though he doesn't have anywhere near the strength of the bigger guy, he's still moving faster and can do it for 5 times the distance before he gets tired of it. Now the body builder is torque, and the kid is HP. Does that pretty much sum it up, or am I just not focusing anymore? haha

 

[TooFst]

(How did I know this one would be around awhile) I do know a lot gets lost between the motor and the rear wheel. You guys should discuss how we can keep more of it on the ground instead of bickering. C'omon help a brother out.

 

[upthemaiden]

who's bickering?

 

[gbalias]

hahahaha.

im loving this thread.

all the explanations......awesome.

and no one knows the derivation of the constants.

haha