A fast road car is a lovely thing and for the majority of performance enthusiasts the capability provided off the shelf is more than adequate for any public road. Very few cars out of the box can turn this road prowess into usable track performance, the Porsche GT3, Z06 Corvette, Ford Mustang Boss 302, and BMW M3 CSL prove exceptions from the norm. Here at Cantech we see track vehicles often and provide tuning options to optimize a car for the heavier demands of track use.
A customer of ours has a very unique car and has caught the track day bug bad. The car is a Pontiac G8 GXP. A limited production 4 door saloon very similar to the Australian born Holden Commodore. The beast already has big Brembo brakes, an aluminum block LS3 V8, and the ubiquitous Nürburgring tuned chassis.
This car is proving to be quite the monster on the track. It has already been equipped with upgraded engine internals and a supercharger boosting output to near 550 horsepower. After consultation with the owner we learned that while the car devoured any straight, corner exit speeds were slower than would be expected, and there were signs that the rear end of the car was experiencing unwanted geometry changes under hard acceleration and cornering.
The rear subframe is flexing in the chassis to the point that this bushing is contacting the body, as can be seen by the grooves in the upper right.
Here is the rear subframe of the car with bushing inserts installed. Control arm, trailing arm, and radius rod bushings were replaced with solid polyurethane. The subfame bushings seen above used an insert that stiffen the existing rubber units.
Though the G8 chassis is very similar to the latest generation Camaro, we learned during a previous visit of this car to the shop that very few parts developed for the Camaro work on the G8. Fortunately there is a company with roots in Australia that offers a bevy of go fast goodies that are compatible. Pedders (www.peddersusa.com) has been in the suspension tuning business for over sixty years and has an extensive line-up of products for the G8. The folks over at Pedders were very helpful with recommendations and provided much appreciated support that was provided to us and the vehicle owner. A package was put together to address the excess chassis flex that included a comprehensive bushing kit and in order to fine tune the ride on the track a gorgeous set of coil-over shocks/struts were purchased.
Pedders Supercar Coil-overs provide adjustment for compression and rebound damping plus independent spring pre-load and ride height tuning.
While the GXP was here our customer requested mounting and match/mount balancing of new Hoosier slicks and Hankook rain tires on some lightweight OZ Ultraleggera wheels.
Pedders Supercar Coilover kit. Top photo: Front; Lower Photo: Rear. Red polyurethane bushings help to quell unwanted flex.
Aggressive alignment Specs provided by Pedders Suspension based upon their experience with the chassis.
Final ride height-shown with stock wheels and street rubber.
Track season will soon be upon us and we look forward to hearing reports from the owner of this car concerning feel, stability, and trap speeds. Preliminary test drives show a car that is more eager to turn in and a more stable rear end less likely to do the chicken dance on track. Stay tuned right here as this car progresses closer and closer to race spec.