Competition dyno, what gear?

[puffincoal]

i'm going to dyno the old coal train and i realized that this being my first 6-speed i had no idea what gear was a 1:1 ratio, i sure this is something everyone knows but me so please help



thanx Aaron

 

[Diesel Freak]

If you have a HX40 or smaller turbo and the dyno is a Dynojet (inertia dyno), use 5th (it is 1:1)



If you have a turbo larger than a HX40 and it is a Dynojet, you may get better TQ numbers in overdrive.



If it is a Mustang (load dyno), use 5th regardless of turbo.

 

[DavidTD]

I suggest you use OD if on a Dyno Jet. Diesel Freak is correct if you are loading, use 1 to 1 ratio.

 

[RustyJC]

My 4. 10 gears may make my experience unique, but here are actual results from 4 Dynojet runs, 2 in 5th and 2 in 6th:



5th gear (1:1) - 320 BHP and 650 lb-ft torque

6th gear (OD) - 347 BHP and 762 lb-ft torque



Not to get involved in the physics of it, but with the 4. 10's, the dyno run in 5th gear takes so little time (in seconds) that the rotational inertia of the drivetrain (crankshaft, flywheel, clutch disk, pressure plate, rotating elements in the transmission, driveshaft, etc. ) was large relative to the rotational inertia of the drum. In 6th gear, the dyno run takes longer (in terms of time), so the BHP absorbed by the drivetrain is lessened (delta rotational inertia/delta time).



Rusty