Author Topic: HP or Torque (Read 659 times)

FUNKED1 · « **Reply #15 on:** May 10, 2005, 01:30:39 AM »

Definitions:
P = Power [lb-ft/s]
Tau = Torque [lb-ft]
Omega = Angular Velocity [radians/s]
P [lb-ft/s] = Tau [lb-ft] * Omega [rad/s] (1)

Unit Conversion 1:
550 lb-ft/s = 1 hp
or
P [hp] = (1/550) * P [lb-ft/s] (2)

Unit Conversion 2:
1 RPM = 2*pi/3600 rad/s
or
Omega [rad/s] = 2*pi/3600 Omega [RPM] (3)

So take (1):
P [lb-ft/s] = Tau [lb-ft] * Omega [rad/s]

Substitute (3)
P [lb-ft/s] = Tau [lb-ft] * (2*pi/60) * Omega [RPM]

Then substitute the result into (2)
P [hp] = (1/550) * Tau [lb-ft] * (2*pi/60) * Omega [RPM]
P [hp] = Tau [lb-ft] * Omega [RPM] * (2*pi/60/550)
Which simplifies to...
P [hp] = Tau [lb-ft] * Omega [RPM] / 5252

FUNKED1 · « **Reply #16 on:** May 10, 2005, 01:33:56 AM »

As far as the merits of power vs. torque, one thing to remember. You can always multiply torque with gearing. You can't multiply power. The guy with more power can always outrun the guy with more torque, as long as he's got the right gear.

Roscoroo · « **Reply #17 on:** May 10, 2005, 02:01:04 AM »

Quote

Originally posted by FUNKED1
As far as the merits of power vs. torque, one thing to remember. You can always multiply torque with gearing. You can't multiply power. The guy with more power can always outrun the guy with more torque, as long as he's got the right gear.

not when you throw nitro into it ..

But then thats a totally different animal .

Schutt · « **Reply #18 on:** May 10, 2005, 03:20:16 AM »

Power and torque are diffrent things. When you put them on one graph and use the same scale for power and torque then they intersect.

When you use a diffrent scale then they dont. So what i want to say is they may intersect anywhere they want but it is meaningless, since its only a matter of scale.

FUNKED1 · « **Reply #19 on:** May 10, 2005, 04:36:10 AM »

Quote

Originally posted by Roscoroo
not when you throw nitro into it ..

But then thats a totally different animal .

As long as you've got a crankshaft driving a transmission driving wheels, what I said is true.

Skydancer · « **Reply #20 on:** May 10, 2005, 07:38:27 AM »

I failed Maths O level, so the calculations are very impressive though I have no idea what you are all on about!:lol

Do they mean that I was kind of right or completely wrong!?

Curval · « **Reply #21 on:** May 10, 2005, 08:28:50 AM »

Funked is teh smart. But he plays too many car racing computer games.

Seeker · « **Reply #22 on:** May 10, 2005, 08:38:21 AM »

Savage cheats!

He knoes full well a steam locomotive produces maximum torque at zero revs....

lazs2 · « **Reply #23 on:** May 10, 2005, 08:58:10 AM »

skyprancer... you should stick with bikes.

I think the question is what is more fun. HP will allways make torque.

In my 3700 lb el camino that is a daily driver I have a large engine with a lot of torque (and HP) down low. hyd cam, dual plane manifold, oval ports, vac sec carb etc. I could make more hp and torque at higher RPM but it would kill the low end where the car lives all the time. Lot's of low end grunt get the heavy car rolling and make it more "fun".

My 2100 lb Healey is the oppossite. short stroke 331 with high lift duration solid lifter cam.. single plane victor manifold, big ported heads and big mechanical double pumper with huge amounts of initial advance.

It doesn't need any low end torque to move it out. It reaches 2500 rpm or more a sec after the clutch is out at launch. I need the "time" it takes to get to 6500rpm or so to shift (you are very busy in the car). It is easy to keep the car in the high RPM range where it makes a lot of HP and therefore "fun".

skyprancer brought up Harleys... if they weren't fun... pepole wouldn't ride em.. they are fun because of low end torque. That is where most people use them. The "fun" is 90% of the time.

the jap bikes make theirs at very high RPM's are are "fun" there.. they are light and get there fast but... most people can't use any of the Hp they produce more than about 10% of the time. the rest of the time they are less fun than a torque bike. You have to really be breaking the law big time to enjoy em.

The torque vs hp pictures were missleading to... the "torque" picture showed a buick gn that is a very small turbo v6. not a low end torque motor at all. the speedo was the hp example.. again.. missleading. gearing can take advantage of torque and hp in any car. A big block that only revs 5500 for instance will rev it with 4.11 gears in top or with 2.75's in top gear. A car with no top end torque that revs 8000 will not pull the 2.75's

lazs

Masherbrum · « **Reply #24 on:** May 10, 2005, 09:28:29 AM »

Lazs, once again bests Skyprancer. WTG!

Karaya

lazs2 · « **Reply #25 on:** May 10, 2005, 09:39:08 AM »

well... I would just as soon not be known as "the guy who could best skyprancer." Sorta like "that comedian that beat up the women in the ring"

Another thing... hp with narrow torque range (small highly tuned motors say) are capable of better acceleration times with the right gearing than similar big cube motors with very broad torque bands but... real life.... no matter what gear the tuner motor manages to shift down into... in a contest on the freeway say... the big motor is gonna walk away. that is a huge factor in "fun". Being pushed back in the seat is worth a lot sensory wise.

BMW bikes are sorta that way (to get away from Harleys which skyprancer knows nothing about) their quarter mile times for the oilhead (and old airhead) bikes were not stellar bu... in roll on throttle tests they allways beat the more hyper bikes that could beat em by allmost a sec in the quarter mile and... with very little apparent effort.. this is a function of a broad torque band.

lazs

Angus · « **Reply #26 on:** May 10, 2005, 10:27:18 AM »

Always thought that a hp was the force that pulls what, 75 kg? up one meter in one second.
Torque i generally know as NM.
I had a car, rated 90 hp, 1600 cubic petrol engine, Torque was rated at some 80 nm.
My tractor had a diesel engine, 3860 cubics, rated 90 hp, torque was 341 Nm.

So, how do you figure that one?

Monk · « **Reply #27 on:** May 10, 2005, 10:44:53 AM »

Quote

Originally posted by lazs2

Another thing... hp with narrow torque range (small highly tuned motors say) are capable of better acceleration times with the right gearing than similar big cube motors with very broad torque bands but... real life.... no matter what gear the tuner motor manages to shift down into... in a contest on the freeway say... the big motor is gonna walk away. that is a huge factor in "fun". Being pushed back in the seat is worth a lot sensory wise.

Yup, that's what I'm seeing with this car. the pull on the autobahn in 5th or 6th gear from, say 60mph to 100mph is "fun". The top speed is about 135, but getting up there. Yes, that's fun. Not a big engine or car, but very surprising.