I have a 833 od 4 speed. Had it on a chassis dyno with the runs made in 4th gear. Will the Hp and torque results be different than if I had a standard 833? Is there a formula to correct for this?
Thanks
Thanks
Chassis dyno with od trans
- Thread starter Backally
- Start date
-
anarchy0392
Well-Known Member
Yes it will be way different if you do a dunno you need to do it in you gear that's closest to direct to drive or a 1:1 gear ratio never in overdrive.
67Dart273
Well-Known Member
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
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
Just go back and do it in third.
mderoy340
Well-Known Member
x2 third gear is 1:1 in an OD manual tranny
67Dart273
Well-Known Member
If the dyno shop still has the files, they can probably just re-calculate and print out a new graph.
All a dyno really measures is torque. HP is calculated from torque. You can do that yourself if you have a torque curve. In fact, you can plot ALL 4 GEARS from one torque curve, by the same method.........just multiply by the gear ratio
I may but at $250 just to load it up and make the first run gets steep. Wasn't real happy with them, may do it in the future with a different shop.
I still have the graph, I would assume they keep a data base also. May go down and seed if they can. Not really a big deal, but would like to have a ballpark number of what my engine has.
Thanks all that responded
Bob
-
