Redline Motorsports And Pfadt Race Engineering Put A C6 On The Fast Track To Road-Course ProwessFrom the January, 2011 issue of Vette
By Michael Galimi
Photography by Michael Galimi
The modern-day C6 Corvette packs a serious punch from the factory, with the three available LS powerplants ranging from the 430hp LS3 ('08 and newer) to the 638hp LS9. And when that isn't enough, it's easy to open up a copy of VETTE and browse the latest go-fast goodies such as exhaust mods, camshaft upgrades, and even forced-induction systems. The lure of big power numbers eventually wears off, however, at which time it's a good idea to upgrade the suspension for better handling to complement the extra grunt under the hood. That's not to say the Corvette-of any generation-lacks in the handling department. Chevy's sports car has always been known for its prowess through the turns, and the latest C6 is no exception. But, as always, there's room for improvement.
Enter Pfadt Race Engineering. The company offers 15 different a la carte suspension upgrades for C5 and C6 Corvettes; we selected its adjustable coilover shock kit coupled with a set of C6 Z06 Corvette Racing sway bars (heavy-rate) front and aft to test on a serious street Vette.
Our test vehicle is not the average Z06, as it's the flagship of Redline Motorsports, a high-performance Corvette and GM specialty shop located in Schenectady, New York. The silver C6 gets going in a hurry, thanks to a 432ci LS7 with an APS twin-turbo kit; all told, it cranks out 840-plus rwhp but can top 950 if the boost is cranked up and there's race gas in the tank. The car has gone mid-10s at 143 mph in the quarter-mile with Redline's Howard Tanner driving, on street tires, and granny-shifting the six-speed manual transmission. The power under the hood not only overpowers the Michelin Pilot Sport tires (345/30-19 back and 275/35-18 front, mounted on CCW 505A wheels) at the dragstrip, but also when Tanner pushes the Z06 hard through the corners on the highway and backcountry roads.
The first step for Redline's Howard Tanner was to measure the ride height at all four corners. The front checked in at 23 13/16 inches on the right and 23 11/16 inches on the left. (The difference was traced to a bad bushing.) The rear heights were 24 7/8 inches on the right and 24 9/16 inches on the left.
We began by stopping off at Albany-Saratoga Speedway (Saratoga, New York), to run the car on the asphalt oval and establish a baseline. The track recently upgraded from a dirt oval to a paved one as a way to attract street cars for special street nights and timed sessions. Using Albany-Saratoga Speedway served two purposes; first and most obvious was that it gave us a place to perform before-and-after testing to verify that the Pfadt parts were effective. The second reason was the paved oval offered us tight turns and no major straights, so Tanner couldn't get the car's blown stroker cooking. The oval is the closest representation of the average street thrashing at realistic speeds, thanks to corners that are similar to an off-ramp, a twisty highway, or a small parkway.
"The car barely sees track time, so I wanted to upgrade the suspension to something that was better performing on the street and rides nicer," said Tanner.
We established a baseline by making several runs and took our best back-to-back laps. The track officials told us that the regular street crowd measures its times in two-lap increments. Tanner's best two-lap time was 46.30 seconds. It wasn't bad considering the extreme heat during our test session (95 degrees on a sunny July day), and it was Tanner's first time around the oval. We then made the short trip to Redline Motorsports to swap over the parts and get back to the track for post-install testing.
The front sway bar was easily unbolted and removed
The components are easy to install, and getting the car on a lift made it even easier, as Tanner; his brother, Derek; and Redline's head wrench, Bruce Hotaling, knocked it out in a few hours. This wasn't the first Pfadt coilover and sway-bar upgrade the shop had done, which certainly helped speed things along. The factory suspension setup uses a monospring that works well despite being introduced in the '60s. (Indeed, its effectiveness can be seen by the Vette's ability to pull 1g off the showroom floor.) The Pfadt coilover shocks replaced the front and rear monospring and stock shocks. That gave Tanner's Z06 a true independent suspension, with each wheel able to react on its own to any road condition.
The difference is obvious between the stock (bottom) and the Pfadt sway bar. The front OEM piece comes in at 1.2 inches thick, while the Pfadt shows up to the party at 1.5.
The Pfadt bar offers a significant amount of adjustment, with firm and solid mounting. The stocker uses flimsy rubber bushings, a choice dictated by manufacturing cost and ride-comfort concerns
Pfadt sway bars are adjustable and use splined ends to hold the arms in place. They were adjusted per the instructions
The results were immediately noticed on the way back to the track. "Just when you think you're about to start driving a street-legal race car, you start to appreciate what the coilovers and sway bars have done to the car's feel. I always felt the Z06 handled incredibly, but now I realize how much room there was for improvement," opined Tanner.
Adding stiffer sway bars and springs typically has a negative effect on a car's ride characteristics, but that wasn't the case in this instance. Tanner told us that the improved damping and spring rates of the adjustable Pfadt coilovers helped the car stay comfortable without blunting its aggressiveness in turns-and the Porsche-killer setting is only an adjustment away.
There are 16 adjustment clicks built into the Pfadt coilovers; the company recommends starting by turning the knob counter clockwise until it stops, which is full soft. Adjustments are made from there and described by click count for consistent adjustments. For the street, Tanner set his at six clicks from full soft in the front and back.
The front shocks are removed to make way for the Pfadt coilovers.
Like the sway bars, the difference between the stock shock (top) and the Pfadt coilover is obvious. The Pfadt pieces offer adjustable dampening and adjustable springs for ride height.
"The 'six and six' adjustment will give a comfortable ride and increased performance. A lot of people use those settings for mostly street-driven cars and very limited track time, like Howard's car," said Aaron Pfadt, owner of the company that bears his name. We queried the suspension guru on what settings are needed to step things up a notch. "For the track, I recommend 10 clicks from soft in the front and 12 in the rear. That is a great starting point, and you can fine-tailor it from there," Pfadt said. "It stiffens up the dampening, and that is what plays a big role in stiffening the car. It won't be a harsh ride like a race car, but it does firm it up. Most people use that setting on the track, but we do have customers who run those settings on the street and don't mind it." The sway bars were set up to Pfadt's recommended settings, which are explained clearly in a comprehensive instruction manual.
On track, Tanner's initial assessment of better handling was confirmed as the twin-turbo Vette ran a new best two-lap run of 45.20 seconds (a 1.1-second gain) using the street-friendly six-click settings. We checked back with Tanner a few weeks after the on-track testing to see if he was still giddy about the new mods.
"The true test came when I really started pushing the car through the highway on-ramps in the past few weeks. I didn't feel any body roll, and the car felt predictable as I pushed it deep into the turns. Normally, hitting bumps in a turn with a Corvette can be a bit unnerving. The Pfadt true independent suspension, however, allows the car to hit the bump, and the three other wheels stay planted. The suspension mods not only increase the limits of the vehicle but also add control to make it easier to drive. It's very reassuring as a Vette owner."
Here's the adjuster knob to control the dampening of the shock. Tanner has it set to six clicks from soft (front and back) for street use. Track recommendations are 10 clicks from soft up front and 12 clicks in the back.
The bottom of the coilover shock acts as the mount; it's very durable thanks to its billet-aluminum construction.
Ride height is controlled by the spring adjustments, which are handled by two adjuster rings. One is to set the height, and the other is to lock it in place
It might be old technology, but the monospring is still an effective component. The Pfadt coilovers allowed us to remove the monosprings, making the suspension a true independent setup.
The shock-mount bolt holes on the Z06's control arms had to be enlarged to accept the Pfadt coilovers
The shocks bolted in easily...
...once the bolt hole was enlarged.
Once the front end was modified, Tanner moved to the rear of the vehicle.
The OEM mounting bracket was reused but required a few washers to account for the extra thickness of the Pfadt sway bar.
With the stock shocks removed...
...the Pfadt units slid in easily.
A comparison of the rear sway bars shows the stock bar has a 1.11-inch diameter, while the Pfadt checks in at 1.25.
The OEM mounting bracket was reused but required a few washers to account for the extra thickness of the Pfadt sway bar.
After dropping the car and driving it around the block (to allow the suspension to settle), Tanner set up the front corners at 24.5 inches and the rears at 25.
The front end was raised a little for extra ride height, since the APS twin-turbo system has two pipes running underneath the front suspension. "In the end, if the car sits a tad higher but rides and handles better, I don't mind one bit," said Tanner.
On track, the car cut its previous two-lap time of 46.30 seconds down to 45.20. Street feel was greatly improved as well, with a slightly stiffer feel but much better performance.
