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Paul Workman · 07-29-2017

I agree w/ lfalzarano. i.e., "approximately" is right on.

Steve: The formula HP = (TxRPM)/5252 is not in question, but depending on who's correction factor one uses depends on the vehicle. the 0.85 correction factor (CF) is generally accepted to be "accurate" for our cars w/ the ZF trans, but if you compare numbers measured at the wheels to values (supposedly measured) at the crank, it quickly becomes obvious that the CF can very: i.e., there is no concrete or universal CF.

Then there's other corrections dialed in, e.g., air temp, altitude, etc. A quote from one of the car rags years ago: "Within reason, tell me what you want the dyno results to be, and I'll dial up conditions that will give you the results you want to see!"

Want more? Enter the Mustang dyno - designed to consider wind resistance as speed increases, which is deducted from the HP/Torque output display. And, the Mustang too considers temperature and barometric conditions at the time of the test.

Dynojet (inertia type) vs. Mustang: The "Jet" provides relative (before and after) raw data, whereas the Mustang provides massaged data better suited perhaps for predicting actual acceleration/max speed. And as always, "Garbage in = garbage out!" The less the raw (measurement) data is manipulated, the more accurate. Because differences in machines' calibration, i.e., which standard (SAE #xxxx, etc) is incorporated, plus atmospheric conditions entered at the time of the test, results between two machines or machine operators can vary significantly.

So, what to do??? For one, choose whatever machine/operator combination you trust for your application, and limit all your data collection to that combination! And, for another, I focus more on the rear wheel data and relative results/actual track results, and refer to the calculated "at the crank" measurements more for "bragging rights".

07-29-2017	#3
Paul Workman Join Date: Nov 2007 Location: Squires (near Ava MO in the Mark Twain N'tl Forest) - Missouri Posts: 6,466	Re: Calculating torque I agree w/ lfalzarano. i.e., "approximately" is right on. Steve: The formula HP = (TxRPM)/5252 is not in question, but depending on who's correction factor one uses depends on the vehicle. the 0.85 correction factor (CF) is generally accepted to be "accurate" for our cars w/ the ZF trans, but if you compare numbers measured at the wheels to values (supposedly measured) at the crank, it quickly becomes obvious that the CF can very: i.e., there is no concrete or universal CF. Then there's other corrections dialed in, e.g., air temp, altitude, etc. A quote from one of the car rags years ago: "Within reason, tell me what you want the dyno results to be, and I'll dial up conditions that will give you the results you want to see!" Want more? Enter the Mustang dyno - designed to consider wind resistance as speed increases, which is deducted from the HP/Torque output display. And, the Mustang too considers temperature and barometric conditions at the time of the test. Dynojet (inertia type) vs. Mustang: The "Jet" provides relative (before and after) raw data, whereas the Mustang provides massaged data better suited perhaps for predicting actual acceleration/max speed. And as always, "Garbage in = garbage out!" The less the raw (measurement) data is manipulated, the more accurate. Because differences in machines' calibration, i.e., which standard (SAE #xxxx, etc) is incorporated, plus atmospheric conditions entered at the time of the test, results between two machines or machine operators can vary significantly. So, what to do??? For one, choose whatever machine/operator combination you trust for your application, and limit all your data collection to that combination! And, for another, I focus more on the rear wheel data and relative results/actual track results, and refer to the calculated "at the crank" measurements more for "bragging rights".