"The formula for hp is Torque X RPM divided by 5250. A dyno measures torque, and the hp is just a number calculated from the torque. So that is why they cross at 5250."
Lg

This is a quote from one of Lou's threads. Should go on a sticky so we can avoid another debate on how a Dyno measures HP. :yesnod: :lurk:


[Modified by jfpilla, 6:29 PM 12/16/2003]

 

I would love to hear more about this
TTT for ya :iagree:

 

That is basic physics, and continues to be mis-understood. Some dyno shops really confuse people by having different "y" axis for torque and power, shifting the cross point on paper.

hp=torque*rpm/5250 on every engine
torque=hp*5250/rpm on every engine

 

Who is that masked man??? :)

LG

 

This may be a stupid question but i'm just curious, how do you measure hp and torque at the crank?

 

:confused: :confused: :lol: :lol: :lolg: :lolg: :thumbs:

 

When I was doing a lot of dyno runs with my motorcycle the Dynojet dyno actually measured RWHP and it was only able to calculate Torque if you hooked an inductive pickup to a coil or plug wire. I am not sure if the car dynos work the same way.


This HP vs Torque article is good:
http://www.vettenet.org/torquehp.html

 

I wonder if Lou quoted James Watt, the inventor horsepower. ;)

 

On an engine dyno . Chassis dynos measure rwhp/tq. While we're on the subject - here is one of my favorites on TQvs HP http://mclements.net/mrc-PowerTorque.html#_ftn1. Easy, fun reading. :thumbs: FWIW>
joel

 

A rear wheel dyno measure HP directly, by measure acceleration of a drum.

Accel x speed x weight (inertia) x constant = power

A Vericom etc works the same way, but uses linear acceleration of the vehicle instead of rotating acceleration of a drum

A flywheel dyno is different, it measure torque. They apply just enough load to stop the engine from accelerating, then measure it accross the rpm range. The load (torque) can then be converted into HP

 

There are at least a couple of different types of dynos in use. The popular Dynojet dyno calculates HP from the vehicle's ability to accelerate a drum of known weight. Dynojets can't apply a differing load to stop the aceleration and therefore you have to do a "pull" that runs through the engine's RPM range. An eddy current dyno acts more like the brake dyno described above. Note that manufacturers' HP ratings are expressed in BRAKE HP (BHP) because they are obtained using the brake dyno as described above.

The key point I think we need to take from the first post in this thread is that HP and TQ are interrelated. Neither one is more important than the other. People get confused by the fact most people quote the PEAK HP and TQ numbers, but that doesn't tell the whole story. There's that saying that people buy HP but drive TQ. What they really mean is that the peak HP figure obtained at 6000 RPM is not very important when most folks drive around at 2000 RPM. In that case, the power (HP) the engine produces at a given RPM is more important. Since it happens that TQ typically peaks much lower than HP (and the TQ curve tends to be flatter), the TQ figure is thought to be more important. However, I'd say what really counts is the TQ and HP produced at the RPM level you tend to drive at.

Whatever. Back to work.



[Modified by Duck916, 6:38 AM 12/18/2003]