Chassis dyno with od trans

You can correct them somewhat. There are formulas to correct torque figures by the difference in gear ratio. What is LESS accurate is estimating the power loss caused by the gear train, as 3rd gear in an OD is the "straight through" gear, and your OD will have more loss.

Essentially, torque is a simple multiplication problem. If you have X torque in a straight through gear, and the overdrive is .85, then you have to convert that back to "as if" it would be 1:1

To go backwards, if you had 1000 ft lbs of torque 1:1 and the OD was .85, then you'd have 850 ft lbs in OD

So to go the "other way" just divide the torque figures that were produced in OD by the OD ratio of the gearbox. In this example, 850 ft lbs would be on your dyno chart in OD. IF this OD is .85, then divide 850 / .85 and you get.............. 1000 ft lbs