Originally Posted by Christian and Beccy
At least on a chassis dyno the car runs in its 'road trim', with all the ancillaries that it runs on the road. Not a dyno-specific exhaust, cooling system and so-on.
As said above, the 50psi thing is what DD have discovered to be the best pressure for consistency. Similarly, their system was designed to use 3rd gear, so we don't question it. Those who use 4th gear on a DD Dyno might aswell have not paid Dyno Dynamics prices and just gone for something cheaper as by altering the suggested methods, you are simply providing an inaccurate figure.
On the tests we have done, the car usually produces the expected figure in 3rd gear and, believe it or not, a lower figure in 4th!!
You should question it imo, for all the hype regarding DD rollers, you really should know exactly why you do certain things. That isn't a pop at you btw, and putting 50 psi into the tyres is hardly running in road trim.....
And yes, I do believe you when you say 4th gear would give a
lower reading (gearbox = torque multiplier)