First off, the pinion angle.
Pinion angle is a topic often discussed in drag racing performance. I'm certainly no expert but I have experience in setting up driveline angles on heavy equipment so I understand the basics and perhaps more importantly what the consequences are with a less than optimum setup.
The IRS setup in the Mark VIII greatly simplifies the discussion since for all intents and purposes, the differential carrier is fixed in position and doesn't rotate with the suspension components as in a solid axle car. Ideally, any movement of the housing is minimized with performance bushings for the mounting points. I currently have poly bushings on the front mount along with a pinion brace. I have drilled through and bolted the rear mount to effectively make it a solid mount to work with the steel rear cover brace. The plan is to optimize the pinion angle with solid mounts on the front mounting tabs.
I used a digital level (that was included with the QuickTrick Alignment kit) to measure all the angles of the driveline. Basically you measure the axis of the transmission, driveshaft and differential to calculate the operating angles of the driveline.
My measurements, front to rear, were as follows:
Centerline A (Transmission) measured 3.3 degrees down (front to rear).
Centerline B (Driveshaft) measured 1.05 degrees down.
Centerline C (Differential) measured ~7 degrees down.
Angle 1 (Transmission to Driveshaft) calculates to be 1.25 degrees.
Angle 2 (Driveshaft to Differential) calculates to be 5.95 degrees.
In a truly optimized setup, angles 1 & 2 would be equal and between 1.0 and 2.0 degrees. The objective here is to minimize the operating angles of the universal joints resulting in less parasitic driveline losses.
In my case, I need to lower the front mount of the differential housing, decreasing the angle of the differential and subsequently increasing the driveshaft angle. If I can get the differential axis equal to the transmission axis, the resulting operating angles should fall to within tolerance.
