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Old 02-15-2009, 01:21 PM   #1
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Default Torque and horsepower

Ive just been wondering why is it that some cars make more torque at the same horsepower then other motors.

For example ive seen dyno charts with 250 rwhp and aroudn 240 tq from a Greddy based set up yet other cars producing the same rwhp dont get nearly as much torque?

Do the turbos affect the difference between the peak hp/tq or am i just completely wrong and for all the same motors you get the same ratio of torque / rwhp.
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Old 02-15-2009, 01:39 PM   #2
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Torque is leverage you make. How much force the motor exerts per unit length. IE- torque is measured if ft*lbs. (a length times a force).

Power is the derivative of torque with respect to time. The rate of change in torque as time (RPMs) changes. As you spin the engine faster, there are more torque events happening so to speak so power starts to go up. (RPMs increasing) But eventually you spin the motor so fast that it can no longer get a full charge of air/fuel in the motor, burn it efficiently, and get it out. When this happens, torque starts falling off. (around 4500-5000) HP is the derivative of torque. So if torque is holding flat, HP is going up. But if torque starts to fall off some, HP will start to level out and stop climbing. (6000-6500) If torque falls off too hard so will HP.

Indeed peak HP and torque numbers can be different. Look at a B18 honda engine for example. They can spin to 9k and breathe, so they might make 180 ft*lbs of torque and 300hp.
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Old 02-15-2009, 01:55 PM   #3
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Quote:
Originally Posted by patsmx5 View Post
Torque is leverage you make. How much force the motor exerts per unit length. IE- torque is measured if ft*lbs. (a length times a force).

Power is the derivative of torque with respect to time. The rate of change in torque as time (RPMs) changes. As you spin the engine faster, there are more torque events happening so to speak so power starts to go up. (RPMs increasing) But eventually you spin the motor so fast that it can no longer get a full charge of air/fuel in the motor, burn it efficiently, and get it out. When this happens, torque starts falling off. (around 4500-5000) HP is the derivative of torque. So if torque is holding flat, HP is going up. But if torque starts to fall off some, HP will start to level out and stop climbing. (6000-6500) If torque falls off too hard so will HP.

Indeed peak HP and torque numbers can be different. Look at a B18 honda engine for example. They can spin to 9k and breathe, so they might make 180 ft*lbs of torque and 300hp.
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Old 02-15-2009, 02:22 PM   #4
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Quote:
Originally Posted by Ajb View Post
Ive just been wondering why is it that some cars make more torque at the same horsepower then other motors.

For example ive seen dyno charts with 250 rwhp and aroudn 240 tq from a Greddy based set up yet other cars producing the same rwhp dont get nearly as much torque?

Do the turbos affect the difference between the peak hp/tq or am i just completely wrong and for all the same motors you get the same ratio of torque / rwhp.

It is weird, just take it for what it is.
I've tried figuring it out. In theory Hp is a derivative of torque. But at the same time you can have a 220hp car with 300ft/lbs of torque.
And the old 5.0 HO's would actually lose torque with headers added.

It is one of those things where there are so many varibles, and even the old some motors work better than others varible.

I just think of it like my Physics teacher told me. Some things work that way just cause they are. There is no logic, it just works that way.
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Old 02-15-2009, 03:35 PM   #5
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Im sure there is logic somewhere....
So when i get on the power do i feel the torque or the hp. Im just surprised that some people with the same engine make same whp but different tq. Didnt know if there is something that can be done to make you get more equal tq whp numbers.
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Old 02-15-2009, 03:43 PM   #6
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Quote:
Originally Posted by Ajb View Post
Im sure there is logic somewhere....
So when i get on the power do i feel the torque or the hp. Im just surprised that some people with the same engine make same whp but different tq. Didnt know if there is something that can be done to make you get more equal tq whp numbers.
You feel the torque. If two engines make the same hp but with different torque, look at the RPM the power/torque was made at, since hp is basically torque x RPM. As for the last sentence, forget about it.
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Old 02-15-2009, 03:54 PM   #7
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This stuff's hard to explain. You really just need to read up on it a bit.

If you could maintain 200 ft*lbs of torque from 2K RPMs to 50k RPMs, you'd make several thousand HP. Because as long as torque is holding flat, HP is climbing. Even if torque was slightly dropping all the while, HP will still keep climbing, just not a fast.
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Old 02-15-2009, 04:06 PM   #8
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Since Pat now has me reading mechanical books ; I'll quote from one of these:
"Torque is the measure of the turning effort produced on the crankshaft by the pressure from the burning gases acting on the piston during the power stroke".
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Old 02-15-2009, 04:09 PM   #9
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Quote:
Originally Posted by patsmx5 View Post
This stuff's hard to explain. You really just need to read up on it a bit.

If you could maintain 200 ft*lbs of torque from 2K RPMs to 50k RPMs, you'd make several thousand HP. Because as long as torque is holding flat, HP is climbing. Even if torque was slightly dropping all the while, HP will still keep climbing, just not a fast.
Here's an example of what Pat is talking about. This is the dyno plot of my engine after the build but before boost:
Attached Files
File Type: pdf HEX_Dyno-NA_PostBuild.pdf (137.2 KB, 137 views)
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Old 02-15-2009, 04:21 PM   #10
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You feel the torque. If two engines make the same hp but with different torque, look at the RPM the power/torque was made at, since hp is basically torque x RPM. As for the last sentence, forget about it.
To be specific, you don't FEEL torque. Torque is just a measurement of rotational force; unless you're the crankshaft, you don't feel it. You FEEL the jerk force, or the change in acceleration.
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Old 02-15-2009, 04:30 PM   #11
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Originally Posted by Savington View Post
To be specific, you don't FEEL torque. Torque is just a measurement of rotational force; unless you're the crankshaft, you don't feel it. You FEEL the jerk force, or the change in acceleration.
To be more specific , you don't feel the change in acceleration. You feel the change in velocity w/ respect to time, which is acceleration. The acceleration is caused by the torque at the wheels pushing against the road.
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Old 02-15-2009, 06:09 PM   #12
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Quote:
Originally Posted by Savington View Post
To be specific, you don't FEEL torque. Torque is just a measurement of rotational force; unless you're the crankshaft, you don't feel it. You FEEL the jerk force, or the change in acceleration.
splittinghairs.gif
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Old 02-15-2009, 07:20 PM   #13
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Lets just say we have a 87 302HO stock, and a 93 302 Cobra motor.

The 87 302 has 225hp (actually more like 250hp with 87's Air Density and cam) But 300ft/lbs of torque @ 3200Rpms.

The 93 Cobra motor only has 280 ft/lbs of torque with more HP.

The 87 will rocket out of the hole, and rip in the 1/8th mile, even against alot of way higher hp cars. But it snuffs out quick. And you don't want to race from like 50 mph on, while you are on the highway. They will own you.

Now the 93 Still fast out of the hole. But it is more of a mid to top end motor, Compared to the stock 87. It only has around 280ft/lbs of torque at a higher RPM. But it breaths up higher in RPMs and will rip the stock.

Basically when old timers are throwing out the slang, torque motor and HP motor. They are basically refering to the above instance. Like if the motor just blast out but runs out of snuff quick. It is considered torque'y. And if you have to have the rpms up to get the power you want they call that a hp motor. It doesn't have much torque to move it without having the RPMS up. And if the RPMS fall some, It loses power fast and may stall.

That is why 4WD guys always prefer torque motors. They have the power to keep going and not stall. But they might suck on a drag race.

There are many things you can change to get your power and torque in the range you want.
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Old 02-15-2009, 11:18 PM   #14
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HP = TQ X RPM/5252.

HP is a measure of work output, just like Watts, etc. Given two same cars, all else equal, the car with more POWER at the same RPM and with same gearing will be faster. It's motor is outputting more work (energy per unit time) so it will accel faster. Your Mustang with gobs of down low torque makes more HP at lower RPMs, which helps it out of the hole, and in a drag race, having strong accel out of the hole makes up for a whole lot by the end of the track.

Look at it this way, F1 cars are fast, yeah? well 800bhp at 16,000RPM = 267ft*lb torque. Not much twist, but with proper gearing, you can exploit that power and get huge amounts of thrust at the wheels.

Or look at diesels, gobs of torque but weak on power. Then you look at their 0-60 times and they're pathetic.

The other thing to look at is overall shape of the torque curve. If it's nice and flat, it can be much faster than an equal car with a peaky torque curve that has either no bottom end, or no top end.
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Old 02-15-2009, 11:27 PM   #15
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Old 02-16-2009, 12:21 AM   #16
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Touché Brain... Area under HP curve over RPM range of operation is the better metric...

but I was thinking something more like the plot below.
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Torque and horsepower-hp_tq.jpg  
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Old 02-16-2009, 05:14 PM   #17
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Quote:
Originally Posted by patsmx5 View Post
To be more specific , you don't feel the change in acceleration. You feel the change in velocity w/ respect to time, which is acceleration. The acceleration is caused by the torque at the wheels pushing against the road.
We might be back to splitting hairs, but I like Savington's definition more. We get a kick from changing acceleration (called 'jerk'), wherease constant acceleration gets old fast. Think of the take-off roll on an airplane. The initial acceleration is exhilirating, but half-way down the runway it's pretty ho-hum (even though the measured rate of acceleration is still pretty fantastic).

This is one reason that some modern cars with extremely flat torque curves don't feel particularly quick, while our turbo cars put a smile on our face everytime we dip into that mountain of mid-range torque.
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Old 02-16-2009, 05:39 PM   #18
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Originally Posted by DeerHunter View Post
We might be back to splitting hairs, but I like Savington's definition more. We get a kick from changing acceleration (called 'jerk'), wherease constant acceleration gets old fast. Think of the take-off roll on an airplane. The initial acceleration is exhilirating, but half-way down the runway it's pretty ho-hum (even though the measured rate of acceleration is still pretty fantastic).

This is one reason that some modern cars with extremely flat torque curves don't feel particularly quick, while our turbo cars put a smile on our face everytime we dip into that mountain of mid-range torque.
Yall call it whatever you want. I've had college level physics and calculus, so I define things the way I was taught to. You say you "feel" something when full boost hits. What do you think you feel? What's happening when you feel this? Is your velocity changing at a very fast rate? Change in velocity with respect to time? Is that acceleration? What?

My first post tried to explain this a bit and it went over the OP's and other's respective heads.
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Old 02-16-2009, 06:04 PM   #19
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Here is my simple explanation, maybe it will make sense:

Torque = the power made during each revolution of the motor
Horsepower = how often that power is made (HP is a function of Tq and RPM)

So in theory, 50 ft/lbs of torque makes twice the HP at 8k RPM as it would at 4k RPM. That torque at 8k RPM is happening twice as often.
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Old 02-16-2009, 06:36 PM   #20
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Quote:
Originally Posted by akaryrye View Post
Here is my simple explanation, maybe it will make sense:

Torque = the power made during each revolution of the motor
Horsepower = how often that power is made (HP is a function of Tq and RPM)

So in theory, 50 ft/lbs of torque makes twice the HP at 8k RPM as it would at 4k RPM. That torque at 8k RPM is happening twice as often.
That's far too simple and concise for this crowd.

Sav and Pat - FWIW - When I mentioned what it is you "feel", I was answering a specific question asked by the OP. No need to whip out the slide rules.
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