LS1 torque formula

[Dyno247365]

Can anyone give me a mathematical equation for the torque a stock LS1 makes, figured out by its hp, redline, and...some other number?

From what I'm hearing, torque is almost like a figment of your imagination, which is really weird but it's a measurement derived from the horsepower, not an independent figure.

[2.2 Straight six]

Originally Posted by Dyno247365

From what I'm hearing, torque is almost like a figment of your imagination, which is really weird but it's a measurement derived from the horsepower, not an independent figure.

no, other way round.

horsepower is calculated. it cannot be measured. torque is a measurable force.

horsepower = (torque x rpm)/5252

horsepower is work done, like mass moved in time given.

the higher the horsepower, the more mass moved in either less time or the same time compared to something of lower horsepower.

torque defines acceleration
horsepower defines top speed/ultimate work done.

[2.2 Straight six]

example of horsepower calculation:

finding horsepower at 4,500rpm

formula - horsepower = (torque x rpm)/5252 (this is only right for calculations working in lb/ft and horsepower)

torque @ 4,500rpm = 250lb/ft

horsepower = (250 x 4,500)/5252

250 x 4,500 = 1125000

1125000/5252 = 214.2 horsepower @ 4,500rpm or 214.2hp = (250 x 4,500)/5252

[2.2 Straight six]

Originally Posted by Dyno247365

Can anyone give me a mathematical equation for the torque a stock LS1 makes, figured out by its hp, redline, and...some other number?

the above formula is true for any engine when working in lb/ft and horsepower. you only need the know torque at an rpm to work out horsepower at that rpm. redline is irrelevant and is decided on forces and other things.

[Nate355RS]

So the more torque you make higher in the RPM range the more hp you make. And if your torque stays constant and RPM increases, hp increase. No wonder smaller engine displacement need to unwind to such high RPM ranges to make significant power. Where does the 5252 come from?

[poormillionaire2]

Originally Posted by Nate355RS

So the more torque you make higher in the RPM range the more hp you make. And if your torque stays constant and RPM increases, hp increase. No wonder smaller engine displacement need to unwind to such high RPM ranges to make significant power. Where does the 5252 come from?

The fact that the more torque you make at a higher RPM yields more hp is true, but at the same time, making loads of torque at a lower RPM is much different than making gobs of torque at a high RPM. Making torque at a usable RPM is much more useful than shooting for some high number.
But this is where gear ratios come in. High torque engines require taller gearing, and this is why high revving high horsepower engines and high torque engines can perform similarly on the street.

[2.2 Straight six]

Originally Posted by Nate355RS

So the more torque you make higher in the RPM range the more hp you make.

effectively, yes. if you're making a lot of torque at high rpms you'll make a lot of power too.

Originally Posted by Nate355RS

And if your torque stays constant and RPM increases, hp increase.

torque doesn't stay constant, on the whole engines make more torque lower in the rev range. if an engine makes a similar amount of torque at high rpm as it does at peak torque rpm then yes, hp increases. just like in the above.

Originally Posted by Nate355RS

No wonder smaller engine displacement need to unwind to such high RPM ranges to make significant power.

engine displacement and design has a lot to do with what torque it will make, you'll find a smaller displacement engine can make a similar amount of hp compared to a larger engine which has more torque. this is because rpm plays a factor (more rpm = more mass shifted in certain time slot in most cases) so if the smaller engine can rev higher it may make more toque. this isn't always a given, because many low displacement engines make little torque higer in the rev range.

Originally Posted by Nate355RS

Where does the 5252 come from?

5252 is a factor in the claculations to deal with the measurements used. (hp & lb/ft) it's just an essential number, if you look at lots of physics calulations and formulae you'll see numbers in there that are just "essential". it's complicated..

another thing to note about the 5252 is that if you look at a dyno graph, the power and torque curves will cross at 5252rpm. they have to, it's linked in with the formula. every proper dyno graph will have the power and torque curves cross at 5252rpm. if they don't, then the graph is wrong. (this is only applicable when working in horsepower and lb/ft)

[Nate355RS]

Originally Posted by 2.2 Straight six

another thing to note about the 5252 is that if you look at a dyno graph, the power and torque curves will cross at 5252rpm. they have to, it's linked in with the formula. every proper dyno graph will have the power and torque curves cross at 5252rpm. if they don't, then the graph is wrong. (this is only applicable when working in horsepower and lb/ft)

Ya know, I've never noticed that they crossed at exactly that point, but I guess it makes sense if you multiply by 5252 and then divide by 5252 you would get T=HP.

I did a little research and the torque and horsepower calculations are starting to make sense. The guy that came up with horsepower, James Watt, I guess figured that a horse could move 550 lb one foot in one second, or 500 ft-lb per second, so that's what he based his calculations on. And to be consistant with Revolutions Per Minute(RPM) you can convert 550 ft-lb per second to 33,000 ft-lb per minute.

So if a crankshaft were to make one revolution with one pound of resistance against a one foot radius the crank would have preformed 6.2832 ft lb of work (1ft*2 for the diameter, and then take that 2 and multiply it by pi to get the circumferance of the revolution). And then you take that 33,000 lb per minute, or 550 lb per second, and divide it by the work done per revolution, 6.2832 ft lb, and you get 5252 for 1 ft lb of torque.

Then take the work done per revolution, in this case 6.2832, and multipy it by the RPM and divide by the conversion factor of 5252 to get horsepower.

So,
1ft * 2 * 3.1415 * 1 ft-lb of torque = Work done per revolution with 1 ft-lb of torque resistance
33,000 ft-lb per min (or 1hp) / amount of work done per revolution with 1 ft-lb of torque = Factor to convert work done * RPM to horsepower
(Torque resistance * RPM) / Factor metioned above = Horsepower

Or,

1 hp = 550 ft-lb per sec or 33,000 ft-lb per min
1ft * 2 * 3.1415 * 1= 6.2832 foot-pounds of work done for 1 foot-pound of torque
33,000 ft-lb per min / 6.2832 ft-lb of work done per revolution for 1 ft-lb of torque = 5252
(Torque * RPM) / 5252 = Horsepower

I'm pretty sure all of that is right, if not then it's real close. Seems like it's a lot easier to watch the pretty colored lines on the dynometer and trust they're right.

[Dyno247365]

Okay then what's the difference between the horsepower and rear wheel horsepower?

[Morley]

Originally Posted by Dyno247365

Okay then what's the difference between the horsepower and rear wheel horsepower?

Horsepower is horsepower..it is just WHERE it is measured that is different. All auto mfg's measure their HP at the crankshaft...a chassis dyno measures it at the drive wheels. The difference is that at the crankshaft it is always higher and looks better in ads. Also engine mfg's put their engines in test stands and can there for only measure crankshaft HP. Since each drive line combo will have a different HP loss associated with them it is simpler for them to give you the crank HP.

[92zcamaroperson]

and in case you didnt get that your engine has to work to turn the weight of your drivetrain before any work is done to move the whole car. Also your transmission slips. The older and more worn the transmission the more it slips and the less you get to the ground when under stress. so if you have an old worn tansmission and you go to floor it and the rpms go up and you think your spinning the wheels....you may have a problem lol..i only mention that because that just happened to a guy i know in a blazer.

[Nate355RS]

In the old days they used to measure the engine's horsepower without the parasitic loss of all the accessories. If you look the old muscle cars their numbers are going to be misleadingly high, but since then they have changed that and all horsepower number you see now are with all accessories. Also a manual will put more power to the rear wheels than an automatic because torque converters never full syncs the engine with the transmission. 4-wheel drive cars like the EVOs and some DSMs will also lose considerably more horsepower than a 2-wheel drive because the engine not only has to power the rear wheels but the front wheels also.

They came up with a new way to measure horsepower that some cars are using now, the new corvette is one of them, but I can't really find any details on how it works.

[2.2 Straight six]

Originally Posted by Dyno247365

Okay then what's the difference between the horsepower and rear wheel horsepower?

there's no difference.

the reason the numbers are different is due to what's known as parasitic loss. it takes power to drive the drivetrain. so the gearbox and diff sap power. so the figure at the wheels is less than at the crank.

[2.2 Straight six]

Originally Posted by 92zcamaroperson

and in case you didnt get that your engine has to work to turn the weight of your drivetrain before any work is done to move the whole car. Also your transmission slips. The older and more worn the transmission the more it slips and the less you get to the ground when under stress. so if you have an old worn tansmission and you go to floor it and the rpms go up and you think your spinning the wheels....you may have a problem lol..i only mention that because that just happened to a guy i know in a blazer.

if it's your transmission that's slipping you probably won't be going anywhere. you clutch can slip, when it's worn. but i've only ever heard of "transmission slip" when you've torn all the teeth off your gears.

[2.2 Straight six]

i think Nate's figured it out anyway.

oh he's following in my footsteps...