Dyno Question ?

[HSSSTOY]

Where should the two curves cross(Torque&HP)on the RPM scale? At Dyno day, several club members after reviewing their graphs, showed the curves crossing the rpm scale at approx. 4700rpm range. From other posts(KC for example),the curves crossed at approx. 5200rpm.
The question is, are we getting the correct readings? the Dyno is a DYNOJET,SAE,and elevation corrected. the operator yet to get back to me with an answer...any help is appreciated.

 

[BlueGTS]

They should cross at 5252rpm. When you see them crossing sooner or later than that the HP and TQ scales are different. Make sure to set the scales on both sides of the chart to the same values for each horizontal line.

 

[ruckdr]

Horsepower = torque * revs/minute * 1/5252
Or
Torque = HP * 5252 * 1/RPM

5252 is a constant, and the 2 curves must cross at 5252rpm.
There are many excellent discussions about HP/TQ, on the web if you do a search for same.

 

[joe117]

5252 is where they will have the same number value but the two scales need not be the same numbers on each side. If for some reason you want to get a different scale view of one or the other curves.

 

[HSSSTOY]

Thanks for the explanation guys....In one instance, the two curves (hp & torq) are crossing at 4760 rpm, how does that affect the results? or does it? are we reading high or low, at the max. hp & torq see #'s below, than if the two curves had crossed at 5252 rpm ? What would be the correction factor,if there is any ! Thanks in advance for any explanation. Sorry for so many questions.

(Max. hp 420.3 at 5300 rpm, Max. Torq 466 at 4250 rpm, curve intersection at 4760 rpm)

 

[joe117]

Take a look at the chart. One side of the chart has the numbers for the torque and the other side has the numbers for horsepower.
If you find the x axis line on the torque side that has 400 on it and follow that line over to the horsepower side and you find 400 on that side also, then the horsepower and torque lines must cross at 5252 rpm.

If the numbers on the left and right are not the same on the same x axis line, just look at the torque value for 5252 rpm by reading the torque curve from the proper scale and then do the same thing with the horsepower curve at 5252 rpm by reading the proper scale. The numbers must be the same.

The lines may cross at any rpm if the value scales on the y axis are not the same. You can still read the proper values even if this is the case.

If niether of the above give you the same value at 5252 rpm, then something is wrong with the chart.

 

[HSSSTOY]

Thanks again you guys are great, mystery is solved.