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FX-MAN
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FX-MAN Apr 19, 3:08am - #12576 
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HP and Torque explained...

For those of you who don't understand it, this will help you ALLOT.. all others, this will be like going back to 1st grade, so just bear with me. smile

I found it SOOO MUCH easier to understand gains when my uncle (who builds award winning hotrods and restores classic cars from the ground up) explained hp and torque to me... So I thought I would fill in those of you that don't quite know what it is.

James Watt (same guy who invented wattage) invented HP while trying to determine pulling power of steam engines. 1hp = 550lbs pulled 1 foot in 1 second (about what the average work horse can do).

Torque is HORSEPOWER converted to rotational force using math to convert to radians(how hard something can be SPUN with resistance).

the formula for converting HP to Torque or vice versa is simple

horsepower = torque x (RPM/5252)
torque = horsepower/(RPM/5252)

5252 is the result of converting 550 to something that can be compared to rotations per minute instead of feet per second.

so you see they are VERY closly related. this is also why on EVERY dyno torque will ALWAYS = horsepower at 5252 RPM (hp=tq x (5252/5252)). So.. on a graph TORQUE can remain level (which is a good thing, torque spikes mean your car doesn't always have the same amount of power to turn the wheels), and hp should go at an incline that peaks then dropw. Torque and HP will always cross at 5252 and can't cross anywhere else, hp will aways be < torque below 5252RPM and > above it. Torque peak is just the top spike on a graph that CAN go up and down and up and down, and it's just where the HIGHEST peak occured which doesn't tell you very much at all.

If you compare the torque graph of a GT and a GTS.. yes they PEAK at a 5lbs difference but the average torque across the band of a GTS is MUCH higher, since a GTS torque graph is much more level, and the GT has a sharp spike, the civic torque graph has one of the sharpest spikes you can find.

For fun, if you really want to understand this, just graph HP for a car with a constant torque of something like 150lb -ft, do it simple start at 1000RPM and graph through 7000RPM using the equation above at something like every 200RPM... it's actually cool, when you make your own little dyno graph, then if you start adjusting torque at different RPMs you can see how it changes your HP graph only a little and why... Doing this excercise gave me a MUCH better understanding of what sort of gains I wanted to get, to really tune the car to the type of performance I wanted.. Even to the point of understanding that a small loss in torque peak in exchange for torque gains where the car REALLY needs it, is actually a pretty good thing.. and also helped me to ask intelligent questions to get answers that I needed from guys who really know their shit.. it will also help you understand why you need to look at the graphed dyno of torque to really understand the torque gains (which is also the only thing you should worry about IMO since to increase HP ANYWHERE on the band you have to increase torque at that RPM, Max HP is important too, but this will also help you understand that WHERE the hp maxes is as important if not MORE important that the actual max number since that determines your top speed and a difference of 1000 RPM can mean quite allot in a race).

[ 04-18-2003, 08:13 PM: Message edited by: FX-MAN ]

FX-MAN
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glitch
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glitch Apr 19, 3:14am - #12577 
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great post thumbsup

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Bradcelica
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Bradcelica Apr 19, 3:54am - #12578 
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kewl, great info grin cheers

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edge202
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edge202 Apr 19, 4:45am - #12579 

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Good post cheers
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Michael Aristide
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Michael Aristide Apr 19, 5:24am - #12580 
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Here's another good resource. http://www.vettenet.org/torquehp.html wink

[ 04-18-2003, 10:24 PM: Message edited by: Michael Aristide ]
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FX-MAN
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FX-MAN Apr 19, 5:43am - #12581 
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Wow... awesome page. I love the waterwheel thing 1200lbs of torque and a 6hp peak... hehehe.

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MyCeli8U
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MyCeli8U Apr 19, 2:54pm - #12582 

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The only thing is that a dyno doesn't measure horsepower. It measures torque and then converts it into horsepower with the mathmatical equation you were talking about. There is not real way to "measure" horsepower, it is just a number you get from doing the math at a specific rpm, and measured torque. thumbsup

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FX-MAN
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FX-MAN Apr 19, 4:30pm - #12583 
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yes.. that's right, however the equasion for getting torque from HP can be helpful if you know the peak Hp and RPM for a car, because you can determine torque there. so if you compare the GT and the GTS... 5lb -ft torque difference at peak, but if you compare torque where hp peaks the GT is 98 and GTS is at 124... which is a pretty damn big difference if you ask me.

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Michael Aristide
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Michael Aristide Apr 19, 9:32pm - #12584 
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Quote:
Originally posted by MyCeli8U:
The only thing is that a dyno doesn't measure horsepower. It measures torque and then converts it into horsepower with the mathmatical equation you were talking about. There is not real way to "measure" horsepower, it is just a number you get from doing the math at a specific rpm, and measured torque. thumbsup
Exactly. Horsepower has nothing to do with what you actually feel. Like the page I posted earlier said, if you take your car to its torque peak then punch in, then do the same at its HP peak, the first one will give you a better shove. The torque curve will show you everything about a car's acceleration.
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