Black,
Those drums are part of the Dynometer. They roll with resistance to determine the amount of HP & torque a car has at the rear wheels. (Not at the crank, factory rated HP)
In order to do the test you have to get the car in the nearest gear with a 1:1 ratio. Once up to speed in say in 4th gear, you do the pull to redline. Thats how the HP & Torque are calculated.
Example,
So say my 1st Dyno run on my car being stock I pulled 110 hp and 98 ft/lbs torque @ 7200 rpms in 3rd gear wich is my closest to 1. This goes along with the factory numbers of @ 142 at the crank. (Theres a 30% loss due to transmission/drivetrain)
That was my starting point before I've made my changes to my car. I have since made changes to my car my car dyno's at 120hp and 109 ft/lbs of torque @ 7200rpm. So now I have about 150 hp which was my ideal goal for now.
Heres a picture of a dyno sheet..(not mine)
