View Full Version : Moving I.C. back

rod cole
03-04-2013, 09:38 PM
I am building a G-body. For drag racing you move the uppers up or lowers down to improve launch. Is there a downside to moving the I.C. back as it relates to handling? And if there is how much can you get away with? Thinking it would help accel out of corners in autocross. Thanks Rod

03-05-2013, 06:31 AM
With 4 link type suspensions, typically what improves launch hurts braking. That's why the OEM put the upper link angles "backward" in the first place. The further back the IC, the shorter the swing arm length; which tends to make the car less stable and may introduce more roll steer from the links operating at steeper angles.

Obviously how "bad" it gets depends on where you want the IC located. These are all just general tendencies. There are a lot of them out there, so you should be able to find a combo that works pretty well. Ask Norm Peterson.

03-05-2013, 06:45 AM
What Ray said.

For road courses, threshold braking is vital for best lap times, and carrying speed through the corners is more important than brute acceleration out of the corner. All that said, there's no "always right" answer. It all depends. If it were me, I'd worry more about shock/spring/swaybar tuning than messing around with the link locations.

Norm Peterson
03-06-2013, 10:09 AM
The thing with the G-body is that if you drop the LCAs at the axle, you get an antisquat increase at the same time that axle roll steer decreases. It can still be overdone and I'd expect that at some point you could get into brake hop. Playing with the uppers at the axle end would be the wrong thing to do for autocross. Relocating the uppers at the chassis end might be workable along with further tweaking of the LCA inclination, but then you're into making more significant structural modifications.

All this relocating of pivot points with autocross in mind may need to consider class-specific limitations. Otherwise you might as well pull the uppers down about to axle center height and start from there - which would drag the rear RC down, reduce the roll steer, and not drive anti-squat (and anti-lift/chance of brake hop) as high. IOW, similar to the Art Morrison version of the triangulated 4-link that tested quite well.


rod cole
03-06-2013, 10:24 PM
By bringing uppers down to centerline. You meen to the level point or all the way to the tube centerline which would be 6 plus inches? Also what is youre thought on using a late model mustang axle with the three link setup with a Y type upper arm grabbing the stock upper mounts and going to the ear on the mustang rear. Making the to short ears on a 8.8 no longer a problem. And thanks for the replies. Rod

Norm Peterson
03-07-2013, 06:50 AM
What I'm getting at if you were to stick with the triangulated 4-link is to keep the uppers level and bring them down to axle height. Axle centerline height might actually be a little too low, but if you're going to work with the uppers at all you might as well do it right and get them down off the top of the diff. This does involve some relocating of the chassis side pickups and that attention be paid to the magnitude of the link loads.

There would be a couple of caveats. Link loads due to acceleration and braking would be higher since the vertical separation between UCAs and LCAs would be smaller, and related to that you'd want firm bushings or (preferably) sphericals of some sort in order to reduce pinion angle change under those loads.

You'd most likely end up needing a rear sta-bar to compensate for the lower rear RCH instead of trying to make it all up in the springs. Get away from the OE G-body's LCA-attached rear bar arrangement, as it isn't very effective (you'd end up with a fairly heavy bar, definitely over 1" solid, another 1/16" or so past whatever that would be if tubular). Instead, use either the 3rd/4th gen F-body arrangement that mounts the bar to the axle with endlinks to the chassis or the S197 Mustang version that ties the bar ends to the axle and suspends the middle of the bar off the chassis with wide flat links that look like big endlinks and stay down at or just under an inch tubular.

But now that you've mentioned an arrangement similar to the S197 Mustang, I think I'd build up a bracket between the axle housing ears and another one between the chassis side pickups and just run a plain straight link between the midpoints of each. Some years ago I saw some prototype parts for this sort of arrangement specifically for the G-body (that never reached production that I know of), and it's at least vaguely similar to what Lateral Dynamics produced for a while. PM to be sent.


03-17-2013, 05:35 AM
I helped a guy with a Regal we re did the upper mount into a single upper on right side with new cross member and added in a Fays2 Watts link,,,,works awesome. As for IC we actually tried to get the car balanced and then he remade T tops out of Lexan, made then about 10 lb each over like 20 or so. He dropped weight where he could and we added it back into the FRAME Rails. Yex we kept some of cars original weight, we just tried to get it as low as possible. Works VERY well. We got a larger reat tire under that car and figured out how to get a larger like 255 or 275 /17 up front, he can break over 1 g skid pad on premium street tires and on his Hoosiers he can push it HARD in G meter. We didnt sneak up we just kept car ideas common sense and they work. He ran a road course some where and with his short stroke(3.25) 4 1/8 bore World block it screams. Engine was left over from his circle jerk days. Car definitely works,,mostly by luck.