Greetings,
Sorry I've been away for a while. Dan G., yes, I'll still get my information to you. I'm thinking of contacting GM to see if I can get any of their prints for the frame and suspension, since it would greatly simplify my work.
The chassis/frame/suspension setup I've described has been in service for five years and 40,000 miles now, with absolutely no problems evidenced of any kind.
About my suspension mod's, this was my basic goal:
1.) Raise nominal front roll center from a few inches below the ground, to about 0"-1" above ground. Dropping the UCA inner shafts, and reducing the front ride height by 1" were instrumental in doing this. Raising the front roll center introduces a better camber-gain characteristic, and reduces the front roll-moment for a given centripetal acceleration, which reduces roll angle, or reduces the demand for roll stiffness - as one desires.
2.) Lengthen the front LCA's by 0.56" to make achieving a negative camber easier without many alignment shims, and in order to reduce the front scrub radius. The stock scrub radius designed by GM was huge (about 3-1/2",) and contributes to front-end wander with wide tires over bumpy surfaces.
3.) Important: maintain negligible bump steer, which is easy to miss with spindle swaps and the like.
4.) At the rear, improvements are much more difficult without making radical changes. Here, I took measurements on the stock set-up and found the rear roll center to be an astounding 18.0"
above the ground, and that the rear was designed with 10% roll understeer (i.e., for every degree of rear roll, the axle creates 0.1 degrees of roll-induced understeer.) As I mentioned in an earlier post, the stock design was for 50% anti-squat.
After confirming these facts in a consultation with Herb Adams, we reviewed how to improve matters. Several ideas were discussed. Most involved extensive modifications (which would require cutting the floor pan, for one.) One solution was rejected outright: the GNX rear suspension. Why? because the very short torque arm tends to create unstable tire motion (akin to axle hop) in situations of marginal traction. But the GNX's 11"-high or so roll center is a big improvement on the normal A/G body's towering roll center (although admittedly, a high roll center helps to fit big tires in a small wheel well, by limiting the transverse displacement of the top of the tire under a rear-roll condition.)
The biggest improvement which could be made without extensive modifications, was to drop the LCA attachment points on the axle by 2.0", by welding small extensions to the existing axle brackets.
This creates neutral roll-induced steering characteristics, and 125% anti-squat, which noticeably improves traction under acceleration (but at the expense of unloading the wheels while braking. An adjustable proportioning valve is a must.)
But I'm starting to digress - Dan G., all, I'll get back to you.
Best,
MAP
Sorry I've been away for a while. Dan G., yes, I'll still get my information to you. I'm thinking of contacting GM to see if I can get any of their prints for the frame and suspension, since it would greatly simplify my work.
The chassis/frame/suspension setup I've described has been in service for five years and 40,000 miles now, with absolutely no problems evidenced of any kind.
About my suspension mod's, this was my basic goal:
1.) Raise nominal front roll center from a few inches below the ground, to about 0"-1" above ground. Dropping the UCA inner shafts, and reducing the front ride height by 1" were instrumental in doing this. Raising the front roll center introduces a better camber-gain characteristic, and reduces the front roll-moment for a given centripetal acceleration, which reduces roll angle, or reduces the demand for roll stiffness - as one desires.
2.) Lengthen the front LCA's by 0.56" to make achieving a negative camber easier without many alignment shims, and in order to reduce the front scrub radius. The stock scrub radius designed by GM was huge (about 3-1/2",) and contributes to front-end wander with wide tires over bumpy surfaces.
3.) Important: maintain negligible bump steer, which is easy to miss with spindle swaps and the like.
4.) At the rear, improvements are much more difficult without making radical changes. Here, I took measurements on the stock set-up and found the rear roll center to be an astounding 18.0"
above the ground, and that the rear was designed with 10% roll understeer (i.e., for every degree of rear roll, the axle creates 0.1 degrees of roll-induced understeer.) As I mentioned in an earlier post, the stock design was for 50% anti-squat.
After confirming these facts in a consultation with Herb Adams, we reviewed how to improve matters. Several ideas were discussed. Most involved extensive modifications (which would require cutting the floor pan, for one.) One solution was rejected outright: the GNX rear suspension. Why? because the very short torque arm tends to create unstable tire motion (akin to axle hop) in situations of marginal traction. But the GNX's 11"-high or so roll center is a big improvement on the normal A/G body's towering roll center (although admittedly, a high roll center helps to fit big tires in a small wheel well, by limiting the transverse displacement of the top of the tire under a rear-roll condition.)
The biggest improvement which could be made without extensive modifications, was to drop the LCA attachment points on the axle by 2.0", by welding small extensions to the existing axle brackets.
This creates neutral roll-induced steering characteristics, and 125% anti-squat, which noticeably improves traction under acceleration (but at the expense of unloading the wheels while braking. An adjustable proportioning valve is a must.)
But I'm starting to digress - Dan G., all, I'll get back to you.
Best,
MAP