If you've been keeping tabs on Project Evo X, our 2008 Mitsubishi Lancer Evolution GSR, you know that we've added power and tire. And although the stock suspension hasn't exactly withered as a result, we wanted to add control and adjustability to better exploit the additional width of our Bridgestone RE-11 tires and Volk Racing RE30 wheels.
Being nose-heavy and tall with a MacPherson strut front suspension, the Evo can really take advantage of a lot more static negative camber up front. So camber plates are a given.
We also wanted to lower the car's center of gravity somewhat and rein in the front camber loss due to body roll. This means ride height adjustment and higher spring rates plus--and this is the critical bit--damper valving that can deal with everything we throw at it.
Doing all of these things will improve transient response and grip. As for ride quality, we're willing to deal with a somewhat busier ride in the Evo but the degradation must be minimal. Our target, the GT-R, defines the bounds of what we're willing to tolerate in Project Evo X. A long-travel suspension will help here.
When it comes to handling, there's no question that our problem statement of a streetable GT-R killer is a tall order.
Undeterred, Vorshlag Motorsports has answered the call. Vorshlag, located near Dallas, Texas, have an Evo X of their own. And they've been using it as a mule in honing a range of coilovers and dampers from Netherlands-based manufacturer AST.
We settled on the AST 4200 series coilover kit by Vorshlag. The 4200 kit includes double-adjustable non-inverted monotube AST dampers.
Twelve adjustment positions for compression and twelve for rebound means plenty of ways for us to screw it up. Fortunately the good folks at Vorshlag provided some initial setup guidelines.
The front strut bodies are steel in order to provide additional strength against the side loads that MacPherson struts inherently have to deal with. In the rear, aluminum shock bodies save a bit of weight. I didn't have a scale, but the AST coilovers are noticeably lighter than stock according to my bicep dyno.
Spring rates of the Hyperco coils are 600 lb/in front and 700 lb/in rear. Before you jump to the conclusion that the higher-rate rear springs will promote tail-happiness, you have to factor in the suspension's motion ratio. The rear spring rates are effectively softer due to the mechanical advantage of the Evo's multi-link rear suspension.
Something to consider--rubber acts like an undamped (or poorly damped) spring. And the stock Evo rear shocks are mounted in rubber bushings at each end.
In the AST coilovers by Vorshlag, the stock rear lower shock bushing is replaced with a spherical joint.
Additionally, the AST rear shocks' top hats replace the stock upper shock mounts. Eliminating all this rubber allows the dampers to react to motions that would otherwise be taken up only by the (undamped) bushings.
One more thing--you'll notice that each coilover has two springs. This is not to achieve some weird progressive-rate strategy.
The skinny spring (called a helper spring) is of minimal rate and is simply there to prevent the main spring from unseating when the suspension extends towards full droop. At ride height, the helper spring is fully compressed to coil bind and is basically acting as a spacer.
MSRP of the 4200 series coilovers starts at $2,910. With camber plates, top hats, these spring rates and helper springs, the total is $3,952. The Vorshlag crew have been hard at work developing other options for the Evo X like their inverted 5000 series, though, so contact them for the latest dish.
As always, we'll share the track test results and driving impressions here on the IL LT blog.
Jason Kavanagh, Engineering Editor
ev0ll says:
10:45 PM, 05/29/09
You guys should be talking to John Mueller of http://www.muellerized.com/ if you want a car that handles but also rides well on the street. Hes been specializing in EVOs/DSMs for years...
kyolml says:
12:30 AM, 05/30/09
It has no either pre-load or ride height adjustments?
ace47 says:
09:09 AM, 05/30/09
Thats more like it. But would the spherical joint make that much of a difference in terms of handling?
trackwrex says:
10:26 AM, 06/ 1/09
Thanks for the in-depth JK. Learned something new from you: "Spring rates of the Hyperco coils are 600 lb/in front and 700 lb/in rear. Before you jump to the conclusion that the higher-rate rear springs will promote tail-happiness, you have to factor in the suspension's motion ratio. The rear spring rates are effectively softer due to the mechanical advantage of the Evo's multi-link rear suspension.
Something to consider--rubber acts like an undamped (or poorly damped) spring. And the stock Evo rear shocks are mounted in rubber bushings at each end."