There is nothing sadder than an overweight ballerina. Try as they might to fit into those tights and maneuver around the floor, it just isn't going to happen. We had a similar problem with our 3,800lb-plus Project 2005 GTO. Chattering wheelhop was the closest thing to dancing it was capable of--as the IRS-equipped Poncho was hard pressed to launch as readily as a solid axle F-body. In addition, it could hardly be considered graceful or agile in the corners, hampered by excessive body roll. Our experience with both SLP GTOs seemed to indicate this was an easily amenable problem with the right components, so we turned to none other than SLP Performance Parts to whip our suspension into shape.
"We did a lot of testing on the street and track, and since the IRS limits what you can do as far as changing the geometry, the rear sway bar was the first place we started," said SLP Director of Engineering Brian Reese. "It seemed undersized for the weight of the car and the nature of driving (being that it's a high-performance machine). So we experimented with different thicknesses and added some adjustability to allow straighter launches, and found something that would not incur objectionable ride characteristics." Ultimately, Brian thinks they designed an effective component that keeps consumer costs to a minimum while vastly improving the suspension's capability.
For less than two hundred clams, SLP replaces the weak 16mm rear sway bar with a 19.05mm solid chunk of heat-treated and zinc-chromate coated cold-drawn steel with two end-link mounting points, enabling an adjustable preload for drag racing applications. The GTO Rear Heavy Duty Swaybar (PN 73004) also comes with SLP's low-deflection K-prene polyurethane bushings for even greater resistance to flexing, which causes wheelhop and body roll. The K-prene Sway Bar Link Bushings (PN 73006) accomplish the same task, replacing the spongy rubber bushings in the end links, which connect the sway bar to the control arms.
A set of lowering springs is thrown in for good measure, which will not only lower the GTO about an inch, but will also improve handling responsiveness. The SLP GTO Lowering Springs (PN 70026) should help lower the roll center and provide a more aggressive stance without degrading ride quality. This duality is owed to the progressive spring rate, which is lower at initial compression--gobbling up cracks in the road and such--and higher as the load or g-forces increase. This also means that if you are carrying anything heavy in the Goat (like your mother-in-law or your old parts), you won't have to worry about the tires rubbing. Reese states that the only downside to adding the springs is that it takes away tire clearance in the GTO's tight wheelwells, preventing the use of larger tires.
SLP recommends purchasing its GTO Camber Kit (PN 70027) for anyone with a lowered '04-06 GTO, as the change in ride height will throw off the suspension's camber. While the factory design allows for full adjustment to the front-end alignment, this is not the case with the rear. To rectify this problem, SLP embedded a concentric hub in a set of polyurethane control arm bushings, which changes its pitch or angle as it is rotated via the rotation of the bolt that goes through its center. One hundred and sixty clams seems cheap compared to the cost of replacing unevenly worn tires, not to mention any number of other problems that can possibly result from a misaligned rear.
To install this trick new suspension setup, Reese invited us down to their state-of-the-art facilities in Toms River, N.J. While the shop is no longer open to the public for installs, as SLP is hard at work fabricating new performance parts for late-model GM cars and trucks, an exception was made for us knuckle-draggers.
Follow along for install tips; we'll include after-suspension g-testing in a later story.