eLTwerker

What's the mathematical(or otherwise) relationship of horsepower to torque and vice verse? I've seen #'s greater in hp than torque and vice versa. How is that possible?

Old SStroker

By definition, 1 HP = 33,000 lb-ft per minute. If you do the math, you get:

HP = (Torque x rpm)/5252

The HP number will be less than the torque number at all rpm below 5252, and more than the torque number at all rpm above 5252.

By rearranging the formula:

Torque = (HP x 5252)/ rpm

Example: Nextel Cup engine making 850 hp @ 9000 is making (850 x 5252/9000) or 496 lb-ft (@ 9000).

If an engine made 496 lb-ft @ 4500 rpm it would be making 425 hp there.

That help?

eLTwerker

That definitely helps, thanks! Question-What is horsepower a measure of. I understand toque is a rotational force, but what is horsepower? Also, do you know why 5252 rpms is the significant #? Would the horsepower:torque not be more effected by stall speed, gears, etc?

spy2520

iTrader: (3)

i think horsepower is a measure of lifting force, cant remember where i read that at...

XxGarbSxX

Horsepower is a measure of work done. It is simply force applied over a period of time. It isn't measured, it is calculated. 5252rpm is the magic number because of the math. As stated by OldSStroker, 1HP = 33,000lb.-ft. per minute. This equation came to be when someone (can't remember who) observed how much work a horse (a pony, to be specific) did over a certain period of time. This method of measurement was used because back in the day, if you were trying to sell someone a machine to do the job that was traditionally done by horses, it helped to know how many horses it would replace. Nowadays, we use it because we're familiar with it.

Horsepower is how fast you hit the wall, torque is how far you take the wall with you.

PunkNPonys

iTrader: (2)

Very intresting info, thanks. I was also wondering why LS1's make more peak HP then TQ if i remember correctly back in the day with old school muscle cars wasnt it opposite? The TQ was always greater then the HP. Why is it different in the LS1?

joecar

Horsepower is the rate of doing work.

Work is the force multiplied by the distance moved in the line of the force;
the units of work are (not to be confused with torque) pound-feet or Newton-metres.

Power the rate at which the work is performed;
power is the force multiplied by the distance divided by the time taken,
or it is the force multiplied by the velocity in the line of the force;
the units of power are pound-feet per second or Newton metres per second.

1 HP equals 550 lbft/s equals 33000 lbft/min.

joecar

Peak HP isn't always higher than peak TQ (or vice-versa)...

My stock 2001 WS6 was rated/advertised by the Pontiac literature as 325HP/350ftlb...
these two peak values occur at two different rpm.

Like Old SStroker said, below 5252 rpm HP < TQ, above 5252 rpm HP > TQ
where instantaneous HP is related to instantaneous TQ by HP = TQ * RPM / 5252.

Edit: This equation is not relating peak HP to peak TQ.

joecar

Edited my 2 posts above to add more info.

Muerte_X

iTrader: (1)

You're right, the hp peak won't always be higher, just that TQ >HP is higher before 5252rpms, and HP > TQ after 5252rpms. Your car doesn't make 325hp though.

joecar

lol, I know that literature numbers are made up for marketing purposes, I never dynoed, so I'll never know.

eLTwerker

I don't understand the math of it. How does 5252 come into it? joecar, in the equation power, or hp, is force(torque) X distance(rpm)/5252. I don't see where the 5252 has significance. Conceptually, I can't grasp how the hp(work done at a speed) equal the work input(torque) at 5252 and then exceeds it. Sorry to nitpick, I just want to understand>

PunkNPonys

iTrader: (2)

I realize that HP isnt always higher higher then TQ but for the most part modded LS1s seem to have higher HP then TQ after 5252rpm. Why is this? I also do realize that the TQ is higher until then but what changes? Am i not right in saying that in the old school muscle car days the TQ was always higher then the HP at peak?

3.4camaro

iTrader: (1)

thats because they didnt rev as high as they do now. did all the muscle cars back in the day go to 7000 rpm? no sir, they would redline lower, so they couldnt get into high hp numbers, but still had monster tq numbers.

joecar

After peak TQ (about 4400 rpm on the stock LS1), TQ starts dropping as rpm increases, and from the formula HP is still increasing.

TransAminal

I look at it like this, don't anyone go ape **** on me, its just the best way I can explain it:

Torque is a measurement of how strong an engine is.

Horsepower is how much work that amount of torque can do.

So something like a Honda, with hardly any torque, can make a lot of (relative) power for what relatively little torque it has to work with.

An old 3rd gen 305 V8 from the 80's hardly makes any power, but it still has enough torque to pull your house down.

The Honda does a lot of work with little torque, the 305 does hardly any work with a lot of torque.

joecar

5252 [ftlb.rev/min/HP] comes from either of:

550 [ftlb/s/HP] / (2*pi [rad/rev] / 60 [s/min])

or

33000 [ftlb/min/HP] / (2*pi [rad/rev])

where rad is unitless, and the [ ] show the units.

Edit: 5252 comes from the physics definition of power and work...
work = force x distance
power = work / time = force x distance / time = force x velocity

and in any equation the units must be consistent on both sides of the equal sign.

joecar

No one's going to do anything bad to you...

That's what HP = TQ * RPM / 5252 is saying.

Pick TQ = 400 ftlb (say flat all the way across) and plot HP for RPM going upto 6000.

Now pick TQ = 200 ftlb (say flat again) and plot HP for RPM going to 9000.

What do you notice... HP is a line with slope increasing with RPM (because in these 2 examples TQ was flat across, which in real life it begins to drop after some RPM).

gametech

iTrader: (1)

Anyone who can't understand a SIMPLE! mathematical formula should revert back to the newbie forum. The original poster's question has been asked and answered, with a few side ventures. If anything else is required to explain this, your high school physics teacher should be drawn and quartered.

eLTwerker

You're a jackass. Take you're bullshit elsewhere.