Sorry for messing those up, hate to think you guys have to restart your drawings.
Lower ball joint: 7 1/4" (to the casting line on the ball joint, close to center and a good reference)
Upper ball joint: 16 1/2"
Torsion bar: 10"
UCA front pivot: 19"
UCA rear pivot: 16 1/2"
No biggie, I didn't start until tonight.
So, I did this on a 12"=1" scale, which is the easiest way to fit this layout on to two 8x11 sheets. That also means converions are a bit tight, so measurements are not meant to be absolutes, but rather relative. If we were geting into an actual car set up, I'd plot this across about 4' of paper, or spring for a program. I'll try to scan the plot tomorrow at work and post it up later.
Okay, so the results. Figuring a 235/60 tire, which is shorter than OEM, but using an OEM spec alignment ride height, I come up with around a 3.5-3.75" roll center. Using my crank down the bars until the lower control arms are level method, I get a 2.75-3" roll center. Using the drop spindles with 72b&b's locations, roll center moves up to around 5.25-5.5" high. Coincidently, stock height with stock tires tended to be around the 5" range as well.
Just for grins, rear roll centers are located mid way between the imaginary line drawn between spring eyes and the center of the axle shaft, or somewhere between 11.5 and 14" depending on your spring set ups. Mines on the low end, SS packs or springs with a high arch will be on the high end.
So what's all that mean...good question that is tough to answer for a street car. When I was racing, we tended to set front roll centers in the 3-4" range, rear around 10, and tried to keep the moment lever arm as short as possible by lowering the COG and set it with huge springs rates, like 1000-1200# up front. But this was an asphalt car on high banking. A dirt car would want the opposite so it rolls over more and gets more bite. I'd think a street car would want a compromise between the two because you want it to corner flat, but do not generate large amounts of downforce necessitating large spring rates.
Remember the front roll center is just one aspect of setting up the car. We also want to know the COG location and its relative position to the roll axis. The size of this distance would then direct you towards bigger or smaller sway bars to control body roll. Once you have a general direction in that regard, you then need to calculate roll couple percentage front to rear, which can get real cumbersome real quick. This is further complicated by the fact that with a classic mopar, we only get to choose among 3 decently sized t-bars rates, where the coil spring boys have 30 choices all 50# apart.
So, there is one aspect of the drop spindles. This doesn't even get in to any bump analysis yet, which will be intersting to see since the outer tie rod also drops two inches with this change. Combine that with the anti-dive Hotchkis arms, and it will get real interesting real fast.
