Chevrolet has long prided itself on the Corvette’s versatility, but that doesn’t mean there aren’t ways to improve its capability when the application gets a bit more focused. Case in point is our Petty C6 project. Owner Brian Petty has long contended that his overall vision for the car is that of a solid all-around performer. Still, as time goes on, the package is leaning more and more toward drag racing prowess, specifically.
While the C6 can hold its own at the strip with the factory hardware, it’s ultimately a sports car. And as such, the Corvette suspension is tuned more for road course and autocross capability than fast quarter-mile e.t.’s. This contradiction was only exaggerated as more power was piled on, and the additional weight of the iron block LSX376 and its ProCharger meant that the factory springs and dampers weren’t getting the job done anyway. With that in mind, Petty looked to AFE Control and its PFADT Series Featherlight single-adjustable drag racing coil-over system to help get the car’s suspension in line with the rest of the vehicle.
“I had two goals in mind,” Petty explains. “First, I wanted to be able to dial in my shocks at the track for various surface conditions. Secondly, I wanted to improve the overall ride of the car. Corvettes are set up great from the factory for autocross and road racing. However, I theorized that the coil-overs would improve the ride quality on the street while still retaining the adjustability for aggressiveness at the track as well. That’s a win-win in my mind.”
But suspension tuning has always been a bit of a dark art in the performance world, and in the wrong hands, a poorly adjusted coil-over setup can do more harm than good. With that in mind, we sat down with AFE Control’s Aaron Ogawa to get the low-down on setting up coil-overs for a given application and find out more about how these drag-tuned components do their thing.
More Than Just Stance
As power becomes more and more readily-accessible every day, builders shift their focus to other elements of their setup to find ways to improve performance. After all, horsepower isn’t worth much at the track if it just goes up in smoke.
“The fundamentals of coil-over-shock technology hasn’t evolved much in recent years, but improvements in shock design are constantly being made,” says Ogawa. “For example, our concentric integrated remote canister (CIRC) technology allows us to triple the nitrogen gas volume over a conventional shock with the same shock travel. This results in a more consistent and linear operation throughout its stroke.”
Improving suspension behavior isn’t just about slamming the car to the ground, though. And along those same lines, coil-overs don’t necessarily equate to harsher ride quality, either.
“Of course, when replacing rubber isolated mounts with solid bearings, harshness can increase,” Ogawa explains. “But I would say the majority of poor ride quality issues with coil-overs are due to excessively high spring rates and/or incorrect damping. Properly designed coil-overs with the right spring and damper combo can yield high performance and excellent ride quality.”
With multiple coil-over adjustments available, finding the right balance between the various settings can be daunting. With ride height, the overall goal (for performance driving) is to try to lower your center of gravity as much as possible without compromising suspension geometry, shock travel, and wheel clearance.
“It’s something you really need to evaluate on a case by case basis,” Ogawa points out. “But the important thing to remember is that if you lower the car too much, you can actually do more harm than good. You obviously want to avoid bouncing off the bump stops, and the suspension needs to have some travel to function properly. You also need to consider the car’s roll center or the imaginary line where the car moves around on the suspension. For instance, if you see that the inner pivots of the lower control arm are lower than the ball joint is on the outer pivots, that’s when you’ll typically start to negatively affect the roll center.”
The majority of poor ride quality issues with coil-overs are due to excessively high spring rates and/or incorrect damping. Properly designed coil-overs with the right spring and damper combination can yield high performance and excellent ride quality.
The majority of poor ride quality issues with coilovers are due to excessively high spring rates and/or incorrect damping. Properly designed coilovers with the right spring and damper combo can yield high performance and excellent ride quality.
Compression and rebound play important roles, too. With a single-adjustable coil-over like the PFADT Series Featherlight, both attributes are adjusted simultaneously through one setting. Still, Ogawa says that we’re mainly concerned with the rebound characteristics in this situation.
“When you increase rebound, you’re adding load to that corner – you’d do that because you want to pin it down more. For example, if you’re running a car at an autocross or a road course and the back end keeps kicking out when you’re braking and turning, it wants to unload the rear and rotate as a result,” Ogawa explained. “You’d address that by adding more rebound to the rear coil-overs to pin that back end down – the shocks are stopping the rear end from unloading. And if the car is understeering in that same context, you’d increase rebound in the front to prevent the front end from unloading.”
Drag racing setups generally follow a similar tack of making adjustments to the car’s front or rear, rather than to individual corners (or applying the same adjustments to all four).
“When you launch the car, you want the front end to unload and the rear end to load up,” he points out. “You want to pin the back end down, so I would be looking for an increased rebound in the rear and decreased rebound up front.”
The Petty C6 Gets A Suspension Makeover
Coil-overs like the PFADT Series Featherlight take those drag racing requirements into consideration at the design level.
“Our drag coil-overs differ from our track-spec systems in many ways,” Ogawa tells us. “We decrease both front and rear spring rates for more weight transfer, and front compression damping is slightly increased while front rebound damping is decreased dramatically. Additionally, rear compression is decreased, and rear rebound is increased.”
When coupled with the lower spring rates, these changes in dampening curves allow the front to lift and hold while the rear squats. It’s all done in the name of maximizing weight transfer at launch and traction in turn. And at the end of the day, you can’t replicate that kind of behavior with the factory components on a C6.
“Aside from the ride height and compression/rebound adjustability, the integrated spherical bearings used with the PFADT Series Featherlight coilovers eliminate rubber deflection, allowing the spring and damper to do their job more directly,” Ogawa explained. “Since the Corvette stock suspension uses a composite leaf spring, switching to coil-overs offers more spring rate options as well as weight savings.”
Being able to change springs takes the suspension’s modularity to another level.
“With leaf springs, you’re pretty limited with what you can do,” Ogawa says. “You can change the shock valving, or you can change the spring pack, and that’s pretty much it. But with coil-overs, you can get all kinds of variations not just for the damping, but also the coil springs. The spring rates are interchangeable – if you decided that you wanted to go autocrossing with those drag coil-overs, you could go with different springs, and it would feel like you have a whole new coil-over setup.”
Petty notes that the swap was surprisingly low-impact, too.
“Installation was a lot simpler than I anticipated – the coil-over bolts in exactly where the factory shock is located. The most difficult part was removing the factory leaf spring, which wasn’t much of a problem at all.”
Although it wasn’t a factor in this particular install, Ogawa pointed out that Corvettes, which are equipped with Magnetic Ride Control, will require a separate AFE Control Suspension Logic ESD (Electronic Shock Delete) kit to prevent errors from the OEM body control module and ECU.
As for this C6, Petty wasted little time putting the new setup through its paces.
“The car rides better than any Corvette I’ve ever driven. I have a stock C5, and the ride quality with these coil-overs is significantly better than that. We’ve only had three passes at the track so far, and only one of which was a full 1/4-mile pass under power. Even still, we managed a 10.1 at 146 mph with a very soft 60-foot. And the car didn’t even think about spinning.”
Obviously the factory suspension on a C6 is good, but if you want to unleash a car’s full potential, coilovers are a must. The PFADT Series Featherlight system improved Petty’s Corvette in every way. With better traction and a more comfortable ride, the AFE Power suspension system is the total package.