Calculating torque

[efnfast]

Soooo, the dyno showed 451 RWHP, 15% drive train loss, calculates to 530 CSHP. Now, dyno shows 403 lb/ft of torque. Also 15% loss? That calculates to 474 RWTQ.
'zit work that way? - Steve

[lfalzarano]

Approximately, yes.


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[Paul Workman]

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".

[Dynomite]

Originally Posted by Paul Workman

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".

This is how you get the "formula"

Tech Info - LT5 Horsepower and Torque Calculations

For some more fun

ZR-1/LT5 Technical Calculations
Post 201 - ZR-1/LT5 Technical Calculations
Post 202 - Tech Info - LT5 Horsepower and Torque Calculations
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Post 204 - Tech Info - ZR1 Wind Force, Rolling Resistance, Drivetrain Loss Calculations
Post 205 - Tech Info - LT5 Camshaft Timing Calculations
Post 206 - Tech Info - LT5 Pressure Drop In Oil Lines Calculations
Post 207 - Tech Info - RC SL4-205 injectors (500+ hp) Calculations
Post 208 - Tech Info - LT5 Summary of Camshaft Timing
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Post 210 - Tech Info - L98 Frisbee Horsepower
Post 211 - Tech Info - LT5 Coolant Flow Calculations
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[jss06c6]

Originally Posted by efnfast

Soooo, the dyno showed 451 RWHP, 15% drive train loss, calculates to 530 CSHP. Now, dyno shows 403 lb/ft of torque. Also 15% loss? That calculates to 474 RWTQ.
'zit work that way? - Steve

Nice numbers! Did you re-cam the engine? You're 90 HP over my '91 which has full SW headers and exhaust and tune..

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[efnfast]

Originally Posted by jss06c6

Nice numbers! Did you re-cam the engine? You're 90 HP over my '91 which has full SW headers and exhaust and tune..

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Full porting
4 reground cams
15# flywheel
3.73 gears
Custom tune
Done on a Land and Sea, and I got to tour the factory where the dyno was made.

[jss06c6]

Got it.. going to Port mine this fall and re-tune. Hoping to get to 380 - 390 at the wheels. Pulled my Fidanza and went back in with original Dual Mass setup..

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[efnfast]

I also did light weight pulleys, so I really lightened up the rotating mass, plus I went with a performance clutch. No rotating mass and a grabby clutch....

[lfalzarano]

Bragging rights are earned at the finish line. Measurement only indicate the relative improvement due to a engine modification. Paul is on spot for all the variables that enter into the estimate.


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[efnfast]

Paul, that all makes sense.
My dyno guy uses an SAE correction factor for local weather conditions.
On top of all that, they can program in a cheat factor on the machine and make it say pretty much whatever they want. I.E., they can add or subtract some percentage in the programming that we the end user never sees.