Thanks Koolride! This is what confuses me. Did Ford set this angle because of the angle of the driveline? I know that when torque is applied, the rear end wants to twist in the upward motion. Which is why people shim or set the rear to a downward angle. Hmmmm?
I welded a set of spring pads to an 8.8 last night. My oem housing was set 5* up.
With everything bolted in the car, stock housing, my settings are (going off memory but confident in the numbers):
rockers level for a baseline
pinion 3* up, weight resting on the springs
engine 3* down
In a perfect world the engine, drive shaft and rear diff would be inline. This minimizes the power loss. The reality is they can't be set that way. Drag racers will set the pinion angle (on leaf spring cars) down a bit to allow for the twist in the springs under load. The less angle differential the loss power loss.
It is recommended to alter the spring pad angle a bit if you are running a lot of horsepower. BUT, you must keep the engine and pinion angle within 2* to prevent vibration. I set mine at 3* up and will alter the engine angle to make it work.
I haven't researched it but I would bet using under rider traction bars would not require altering the pad angle if set up properly.