calculating torque...

[wornknobby]

i was reading a 2-stroke tuning book by Graham Bell, and i saw a few eqations on how to find hp, power,road speed, but i didn't find one on how to calculate torque,, now i have a tool for measuering rpms for a car engine, but this only goes as low as 4 cylinders, so i found one from a 2 cylinder snowmobile, now this doesn't have to be the most acurrate measurement, i just want to get a pretty good idea.

i know that what the tach reads will actually be double of what my motor is actually putting out, but to calculate some of these forumlas, i need to know my torque in given gears at given rpms. i found this equation on another site

T = F * d, where
T = Torque
F = Force (here, the force applied perpendicular to the axis)
d = Distance


but i wanted a second opinion on this, as i don't know if there is something i am missing? :coocoo:

 

[CaptainObvious]

From www.howstuffworks.com

http://science.howstuffworks.com/fpte4.htm

 

[wornknobby]

thanks, i just printed out all that stuff about torque, but now i;m stuck, torque =force x distance

well what am i usuing for figures for force? :coocoo:

also is my distance the amout the crank spins until there is no torque being produced? ie. (crank rod is verticle)


sorry for being such a rookie on this, :bang:

when i go to school tomorow i'm going to ask my physics teacher for some help. :laugh:

 

[oldfrt613]

Torque can be calculated if you know the hp at a given rpm - I'll post the formula tommoro.

 

[deerfeedrb]

Calculating torque

From Heywood's Internal Combustion Engine Fundamentals book, P=(N*T)/5252 where P is power in hp, N is crankshaft speed in rev/min, and T is torque in lbf*ft. I hope this helps.

 

[FruDaddy]

I believe that it will be nearly impossible to calculate torque without a dyno. HP is just a derivitave of torque so you must measure torque first (deerfeedrb's formula is the one, that's why every dyno curve crosses at 5252 rpm). Typically, torque is measures as the amount of weight that must be applied to a foot long lever before the lever moves. Hence the term lb/ft or ft/lb. The dyno determines how much force is required to hold the engine at a given RPM. If you find a way to make a homemade dyno, please post directions. If you already know these numbers, then you can get into the torque multiplication numbers where you would have to multiply he final drive but each gear ratio, and the primary drive. Then, I think you multiply the torque reading times the overall gear ratio. I wouldn't want to even tackle it unless I were extremely bored.

 

[wornknobby]

i'm only doing this to see how changing my gearing will affect my overal speed and accelleration. i'm just trying to learn something new :) :cool:

 

[FruDaddy]

Oh, that's simple, lower gear ratios will improve acceleration and hurt top speed. Have someone time you over a given distance with various ratios. If you don't use the top gear at the track, gear it down until you do. This will maximize your acceleration while preventing you from running out of gears. If you top out high gear, consider raising the ratio.