Although in our first round of suspension tweaks to Project EVO, we had obtained a very good compromise between ride quality and handling, we wanted to step it up a notch for track events. Although our original Hyperdamper II setup worked exceedingly well on the street, it was a bit on the soft side for more hard-core track use and time trialing.
The Hyperdamper II has a 30 percent stiffer spring rate over stock. The front springs are rated at 5 kg/mm-280 in/lb up from the stock 3.8 kg/mm-215 in/lb. The rear springs are 6 kg/mm-335 in/lb up from the stock 4.8 kg/mm-270 in/lb. As you can see the stock EVO and even the Hyperdamper II had fairly mild spring rates that are more suited for brisk street driving than turning and burning for trophies on the track.
We replaced our Hyperdamper IIs with HKS' Japan market only, racing calibrated Hyperdamper Pro. The Hyperdamper Pro is found on many of Japan's top time attack cars. It was conceived and calibrated for track use with R-compound tires. HKS deemed it to stiff for general street use for North America but we had heard of this suspension's awesome reputation and begged HKS USA for a set.
The Hyperdamper Pro is a mono tube design. Which means the damper has a single tube and a large valve-containing piston in hydraulic oil under several hundred pounds of nitrogen pressure behind a floating seal. The mono tube design helps disperse heat better; the large piston displaces more fluid per inch of shaft motion allowing more sensitive and accurate damping. The large piston has more bearing area and can offer longer life. The high gas pressure increase the vapor pressure of the fluid, reducing cavitation in the shocks damping valves ensuring smooth fade free operation under all conditions. The Hyperdampers Pros feature 30-way external damping adjustment with the adjusters controlling primarily rebound with some affect on compression simultaneously.
The Hyperdamper Pro unit also has an inverted shaft design meaning the shock body is mounted upside down so the large body of the shock serves as the shaft while the smaller shock rod attaches to the housing internally. Inverted shocks are much stronger and rigid; the EVO with its WRC rally heritage comes stock with inverted shocks. The front struts have an adjustable pillow ball mount so camber can quickly and easily be adjusted, a must for track cars. The rear shocks also have a pillow ball upper mount. Pillow balls eliminated camber-reducing flex in the suspension as well as ensure every millimeter of suspension travel will be controlled by the damper instead of flexing rubber.
One of the coolest things about the Hyperdamper Pro is that the ride height can be adjusted independently of spring perch height. The lower suspension mounts can be threaded up and down so the car can be lowered without affecting spring preload or wheel travel. A low car can have full wheel stroke, a critical thing to ensure consistent balance under all sorts of cornering conditions. We raised the rear ride height an inch higher than HKS had set it and lowered the front of the car to make the wheel well gaps consistent knowing we had not affected our travel. The adjustable mounts also make corner balancing easier because you can affect the corner weight without changing the spring preload. This is a very great and useful feature.
The Hyperdamper Pro has an aggressive 12 kg/mm-670 in/lb spring rate in the front and a 10 kg/mm-560 in/lb rate in the rear. This is a whopping 315 percent stiffer than stock in the front and 210 percent stiffer in the rear. Although these spring rates seem spectacularly high, they are actually a little on the soft side for a racecar. The front springs are a straight rate and the rear springs have a straight rate main spring and a lower rate tender spring, which we suspect is mainly there to keep the short main spring from rattling under suspension extension.
The suspension makes our EVO handle like a racecar. Steering response is immediate, body lean is undetectable while cornering is incredible. The spring and damping rates are well matched. There is no hopping or bobbing and the suspension keeps the wheels planted at speed, even on rough or undulating pavement. We haven't needed to touch the damping adjustments yet.