How do I calculate Torque?

AChevyFan wrote:

> That's a great algrebra lesson but I am assuming that I have neither HP nor
> Torque to calculate so that doesn't help me.
>
Ah, then your only choice is either a dyno session or one of these
accelerometers. With the accelerometer you can compute torque at rear
axle but it also takes a lot of algebra. Knowing the rear axle ratio
you can convert rear axle torque to transmission torque, and ultimately
to engine torque, though that is a bit iffy with an automatic (fine to
do with manual box, however).

I've seen formulas to calculate - or estimate - hp from acceleration data.
If I had nothing and wanted to do better than a guess, I would probably get
one of those G-force accelerometer gadgets.


"Don Stauffer in Minneapolis" > wrote in message
...
> AChevyFan wrote:
>
>> That's a great algrebra lesson but I am assuming that I have neither HP
>> nor
>> Torque to calculate so that doesn't help me.
>>
> Ah, then your only choice is either a dyno session or one of these
> accelerometers. With the accelerometer you can compute torque at rear
> axle but it also takes a lot of algebra. Knowing the rear axle ratio you
> can convert rear axle torque to transmission torque, and ultimately to
> engine torque, though that is a bit iffy with an automatic (fine to do
> with manual box, however).

AChevyFan wrote:

> What is the calculation for torque?
> I know the Horsepower is:
>
> HP = Torque(lb-ft) * RPM/5252
>
> But how do I get Torque?

Not sure what you're asking here. Typically, torque is MEASURED, not
calculated. Horsepower is computed from measured torque.

If you have a horsepower curve and you want to back-derive torque, just
solve for Torque in your equation above: (HP*5252)/RPM

AChevyFan wrote:

> That's a great algrebra lesson but I am assuming that I have neither HP nor
> Torque to calculate so that doesn't help me.

OK then... what DO you have? You have to know something to start the
calculation.

And any calculation that depends on knowing cylinder pressure will have
to be converted to BMEP, and you'll have to know the engine's geometry
as well (bore and stroke). Calculations like that aren't very precise
unless you have a full-blown computer model akin to "Desktop Dyno."

Actually, its first-year "Physics for Engineering Students," regardless
of engineering discipline (even us EEs had to take basic physics and
mechanics.


Kathy and Erich Coiner wrote:



> Get a mechanical engineering degree with emphasis on thermodynamics.
> You will learn this in your 4th year thermodynamics classes.
>
> Erich
>
> "AChevyFan" > wrote in message
> ...
>
>>What is the calculation for torque?
>>I know the Horsepower is:
>>
>>HP = Torque(lb-ft) * RPM/5252
>>
>>But how do I get Torque?
>>
>>
>
>
>

Brian wrote:

> I've seen formulas to calculate - or estimate - hp from acceleration data.
> If I had nothing and wanted to do better than a guess, I would probably get
> one of those G-force accelerometer gadgets.
>
>
If you carefully plot acceleration versus speed, yeah, you can do it.

If you use an average, like a 0-60 time, you will get an AVERAGE torque,
not a peak one, or a torque vs rpm.

Further, 0-60 is too high, because at speeds above about 35-50 mph, air
resistance is using a considerable torque. It would not be just a
function of mass of car. So you'd have to compute acceleration vs speed
up to 30, at several data points. This is getting a bit hard to measure
accurately by a stopwatch and speedometer, which is why actual
accelerometer is good. I have seen some for a little over a hundred bucks.

Using vehicle acceleration to measure hp is useless. We've done it
with airplanes on takeoff, and we get a horsepower figure of about
one-fifth of what we know the engine is giving us. Any movement thru
air represents drag, any rolling wheels represent drag, and the losses
through the drivetrain are significant. Further, unless the engine is
operating at the desired RPMs (redline or max torque) it's all
irrelevant.
The most accurate measurements use an engine brake and
torquemeters. Torque x RPM x 6.28 divided by 33,000 equals hp.

Dan

In late model cars you maybe able to capture the needed data from the
ODII port. The rolling and air drag losses can be calculated. Afar as
the drive train losses you ignore this and what you have is very close
to what you would get from a chassis dyno.
Stan

wrote:
>
> Using vehicle acceleration to measure hp is useless. We've done it
> with airplanes on takeoff, and we get a horsepower figure of about
> one-fifth of what we know the engine is giving us. Any movement thru
> air represents drag, any rolling wheels represent drag, and the losses
> through the drivetrain are significant. Further, unless the engine is
> operating at the desired RPMs (redline or max torque) it's all
> irrelevant.
> The most accurate measurements use an engine brake and
> torquemeters. Torque x RPM x 6.28 divided by 33,000 equals hp.
>
> Dan

wrote:

> Using vehicle acceleration to measure hp is useless. We've done it
> with airplanes on takeoff, and we get a horsepower figure of about
> one-fifth of what we know the engine is giving us.

I know several people who have taken their car to the strip, weighed it,
and used trap speed to compute horsepower, and THEN gone to a chassis
dyno and checked the power that way. They've all said that the numbers
are amazingly close- usually within 10-15%, and nothing like the 1/5
you're talking about.

I would guess that with an airplane trimmed for takeoff with the gear
and flaps hanging way out, the high aerodynamic drag just before liftoff
invalidates the method.

Steve > wrote in message
...
> wrote:
>
> > Using vehicle acceleration to measure hp is useless. We've done it
> > with airplanes on takeoff, and we get a horsepower figure of about
> > one-fifth of what we know the engine is giving us.
>
> I know several people who have taken their car to the strip, weighed it,
> and used trap speed to compute horsepower, and THEN gone to a chassis
> dyno and checked the power that way. They've all said that the numbers
> are amazingly close- usually within 10-15%, and nothing like the 1/5
> you're talking about.

10-15% ?? Struth. With my vehicle performance simulation software (details
on the website) I can get within a couple of percent of true bhp if the
vehicle performance and weights, gearing etc are known accurately.
--
Dave Baker - Puma Race Engines (www.pumaracing.co.uk)