i think this is where i might post this so here it goes.
If when you dyno a car, the idea is to run it through the rpms in the gear with the ratio closest to 1:1. So like in most m5 cars you would use third gear. How then are automatics dynoed? You cant give it full throttle in third gear at anything below say 3500 rpms in a 6000 rpm car or it downshifts to second, so how are accurate numbers obtained below that lowest rpm at which the car wont downshift? Do they just disconnect the kickdown? Thanx.

 

Well, i'm not sure if this holds true to all dyno's, but I know the dyno we have at school you actually run through in 2'nd gear the whole way, I guess that way you can hold a gear, and not have to worry about it shifting and whatnot, because it should be the same through all gears, but you just have to make sure that it stays in that gear otherwise it'll mess up, so they just use 2'nd.

 

but wouldnt torque multipication from a higher gear ratio make for even a little inaccuracy in the positive direction?
not trying to argue, just curious, thanx.

 

I honestly don't know, all I know is they use 2'nd gear all the way up at my school (automotive training center).

 

No; the dyno is looking at both its own RPM and engine RPM, and calculates gear ratio out of its readings.

Think about it for about 2 seconds.... if the dyno had no way of doing that, then how could it accurately measure a 2.73 geared car right behind a 4.10 geared one? Or a truck with 36" mud tires right behind an import with 205/50-14s?

 

Think RB is right... it figures out the gearing on its own and compensates for it in the numbers.