An effective way to identify a nicely balanced Subaru WRX is to listen to the cries from the front and rear tyres. Push a standard WRX through a corner and you'll hear the outside front tyre howling for relief. It screams: "Hey, I'm copping all the load here - gimme a break!"
But the Whiteline enhanced 'P-Rex III' MY03 WRX is utterly different. When you tip this sucker into a corner, both the front and rear outside tyres share the pain equally and, as a result, the chassis is much better poised and balanced.
Instead of being forced to drive around the WRX's inherent understeer, the driver of the Whiteline MY03 has much more flexibility. Sure, you can make the thing understeer into a corner if you provoke it, but overall the chassis is much more adaptable. A mid-corner throttle lift-off will bring on a gentle oversteer. Oh, sorry - you don't like oversteer? Simply spend 5-minutes adjusting the rear dampers and swaybar and you'll have it balanced just the way you like it.
P-Rex III's handling can be configured to suit any driver preference.
Interestingly, tyre grip becomes relatively lacking when you've got the chassis balance and control of the Whiteline upgrade. You see, the standard Bridgestones are fine on the stock WRX, but the sheer cornering loads that the Whiteline car can generate means the car would really benefit from a stickier set of tyres - in dry conditions, anyway.
Jim Gurieff from Whiteline explains: "We always configure our handling kits on the car's original tyres. This lets us find the correct balance and we can raise tyre grip levels from there."
The Whiteline P-Rex III MY03 is the company's in-house development and testing vehicle, which has been subject to extensive road and track trials.
"This car wears pretty well everything we can throw at it," says Jim.
We're talking 40mm adjustable struts, adjustable front and rear swaybars, anti-lift kit, rear camber kit - you name it!
The Base Handling Kit
The platform for P-Rex III's suspension upgrade is the so-called Handling Kit, which is designed to give buyers the biggest "bang for buck". With no optional extras, the Handling Kit gives you upgrade swaybars, an anti-lift kit and a rear camber adjustment kit.
Depending on its intended market, we're told the GD-series WRXs uses solid front and rear swaybars measuring 19mm and 20mm respectively. Whiteline replaces these with 3-position 'blade' adjustable 22mm solid bars at the front and rear (part numbers BSF33Z and BSR36Z). There's some interesting test data related to the fitment of the 22mm rear swaybar. With absolutely no other changes, G-circle tests saw mean average lateral Gs increase from 0.83 to 0.855 and the maximum attainable speed increased from 33 to 39 km/h.
Front-end grip is further enhanced with Whiteline's proven anti-lift kit (part number KCA359). The anti-lift kit comprises replacement front control arm mounts fitted with a relatively low-compliance bush. The mounts are engineered to relocate the control arm pick-up to deliver additional castor, while the low-compliance bush reduces alignment variation during cornering. In the case of a WRX (which is fitted with MacPherson front struts) castor is essentially the angle that the front struts lean back from vertical. The benefit from additional castor is greater camber while cornering (greater 'dynamic' camber).
Whiteline claims their kit delivers an extra 0.5 degree positive castor in static conditions and around 1.0 degree in dynamic conditions. Reduced bush deflection (in comparison to the factory bushes) is the reason for the kit's greater dynamic castor. Unlike the earlier GC-series WRX, fitment of the Whiteline anti-lift kit to a GD-series WRX necessitates a pair of spacers that allow clearance against a so-called "crumple brace". This brace is said to enhance crash performance and has no stiffening effect from a handling point of view.
The final component of the Handling Kit is an adjustable rear camber set (part KCA414). The more serious your intent, the more camber you should dial in - Whiteline suggests a "Touring" rear camber angle of -0.75 degrees, a "Sport" setting between -1.0 and -1.25 degrees and a "Race" setting up to -2.5 degrees.
The base Handling Kit retails for AUD$837 plus fitting (which typically involves about 3 ½-hours labour).
P-Rex III's Optional Extras
In addition to the Handling Kit, P-Rex III has served as a test bed for a range of other items that are separately available.
Most importantly, P-Rex III has been the test bed for Whiteline's new range of Group 4 coil-overs. Jim says these offer a "true" 40mm internal diameter and feature 10-position adjustable bump and rebound force. The 60mm ID springs are carried on height-adjustable platforms and use relatively mild spring rates - 300lb at the front and 225lb at the rear. Unlike the factory struts, the Group 4 units are non-inverted - this means the adjustment mechanism is at the top of the strut and is much less exposed to mud, etc. Unlike many other "converted rally" designs on the market, the Whiteline Group 4 shocks are also specifically designed for road use and reputedly do not require regular maintenance.
The standard WRX rear swaybar mounts have been known to fail when rear sway stiffness is significantly increased. To avoid this situation, P-Rex III carries Whiteline's 'unbreakable' heavy-duty mounts (part number KBR22). The standard swaybar links are also replaced by extra heavy-duty alloy links (KLC26), which offer improved strength as well as providing more direct swaybar actuation.
Jim says there's a relatively limited amount of toe adjustment on the rear wheels of a GD-series WRX. Rear toe-out is generally desirable on a WRX, so Whiteline has fabricated an adjustable front parallel link that should be fitted in conjunction with a replacement lockwasher. The lockwasher prevents the factory rear toe adjustment mechanism from shifting during normal use. Toe adjustment is then performed through a replacement front parallel link (part number KTA107). This adjustable link allows ample toe adjustment and virtually eliminates any chance of toe change in normal driving. Note that low-compliance replacement bushes should also be fitted to both lateral links.
Whiteline's P-Rex III has also been treated to front and rear strut braces (part numbers KSB599 and KSB511). Jim comments that the GD-series Impreza is much more rigid than the previous GC-series Impreza, but strut bracing can still make a noticeable improvement.
In addition to those mentioned above, Whiteline offers a number of optional extras. However, Jim says most are intended for hard-core motorsport use and cause a considerable NVH trade-off. These items include a 'motorsport' anti-lift kit (with an extra-firm bush), rear sub-frame lock kit, diff support lock kit, a heavy-duty steering rack mount kit and a camber adjustment rod for the rear.
In our brief drive we were extremely impressed by the ride/handling compromise of P-Rex III - even with the dampers nearly fully 'wound up' the ride remains more supple than, say, a factory MY02 STi. As discussed, handling balance is vastly improved and can be tailored to suit your specific driving style. Turn-in is crisp (without at any time being nervous ), mid corner-balance is exceptional and the power-exit traction of the AWD Rex rounds out a very impressive package.
And the price, you ask? Well, brand new Group 4 adjustable coil-overs will set you back AUD$3390. Inevitably, the new struts form bulk of the overall price. Add to this AUD$837 for the Handling Kit, AUD$388 for both the front and rear strut braces and AUD$287 for the adjustable rear toe arms and you've scraped in just under AUD$5000 (plus fitting). Five grand isn't chicken feed, but this is still an excellent purchase for anyone serious about street/weekend racing their Rex.