Subaru WRX STI
The Subaru WRX STI is a performance-oriented variant of the Subaru Impreza – a compact car that has been manufactured since 1992 by Subaru. The WRX STI builds further on the standard WRX cars, which were designed with rally racing in mind. To differentiate the STI from the standard WRX Subaru produced the STI with a more track-oriented design which featured a wider body and flared wheel arches as well as aluminum suspension components.
|Production||1992 – Present|
Front Engine, All Wheel Drive
Compact 2 Door Coupe | 4 Door Sedan | 5 Door Hatchback
Modifications to the Subaru WRX STI are extremely popular. While performance upgrades are nothing new, there are some critical building blocks that should be considered to ensure you unleash your vehicle’s maximum potential. Below are a few things worth doing to properly modify your car for horsepower and handling.
Suspension Set Up
Always make the suspension faster than the engine. Ensuring you can turn and stop will always be more important than knowing you can go fast. Getting your Subaru WRX STI suspension dialed in can equate to you out-handling your competition, and depending on your type of racing, will even give you better times. If your vehicle came from the factory with softer suspension, it will almost always handle poorly until the suspension is replaced with a performance setup such as coilovers. Old, worn out suspension also has a very negative effect on the handling and should be replaced, especially if used for any spirited driving where handling is key.
Coilovers help to set up your Subaru WRX STI height and damping, which allows you to lower your center of gravity and stiffen up your chassis for better cornering and control. Not only does your car look sportier (and better in our opinion), but it’s also a key step in allowing you to transform your car into a true performance machine, transferring your modifications into tangible wheel horsepower.
There are many different coilover brands and types on the market, so picking the right one can be daunting. Here are four key things you need to look for when buying Subaru WRX STI coilovers.
1. SPRING RATES
Springs are an integral part of your suspension set up. They control the vehicle’s ability to bounce, absorb bumps and create low body roll when loaded. Higher spring rates require more force to compress the spring, which reduces the amount of suspension travel. The body of your car moves when you accelerate, brake and turn. By reducing body movement, you make handling more predictable and effectively spread the cornering load across all four tires better leading to better grip. Most aftermarket coilovers use significantly stiffer springs than OEM suspension, which improves handling and gives the driver more feel for the road and their car when performing spirited driving.
2. SPRING AND VALVING ADJUSTABILITY
One of the many reasons anyone purchases a set of Subaru WRX STI coilovers has commonly been to lower the car. The lower center of gravity will help reduce excessive body roll and improve performance. Having the adjustability for ride height, spring preload and damping are essential features of a high quality coilover. Adjusting your coilovers can help you fine tune how your vehicle handles and give it the perfect ride height for your application. The ability to replace the springs with stiffer springs is also an important feature as track cars need much higher spring rates than street cars to gain grip, improve handling and reduce body roll. If you swap to a stiffer or softer spring, it’s important to match your spring rate with your damping to avoid a bouncy ride which is ultimately detrimental to handling.
3. TOP MOUNT
On top of the coilover is a mount that holds everything together and bolts the top of the coilover to the car. This mount is known as the “Top Mount” and between the mount and strut assembly are two different types of bushings, rubber or pillowball type. As you might expect, OE manufacturers use rubber bushings because it deflects more and is a primary cause for the failure of suspension precision. The rubber you’ll find on most OEM struts is soft and allows a lot of energy deflection. A stiffer rubber mount improves longevity and reduces energy deflection. A pillowball bushing is a metallic spherical joint which rather than deflecting from the cornering forces like a conventional rubber bushing, pillowball mounts do not move at all. This translates into a far more precise feel from the suspension and steering.
4. MONOTUBE DESIGN
Inside any coilover, there are two designs of dampers you will come across, monotube and twin tube. The twin tube uses an inner and outer tube, twins if you will. The inner tube holds the piston shaft, valve and oil. The outer tube holds damper oil and nitrogen gas. Here’s how it works; when the suspension is compressed, the piston forces oil out of the inner tube by its valve and into the outer tube. When the piston moves back into position, the oil is sucked from the outer tube back to the inner. Most OEM suspension utilizes the twin tube damper set up because it allows for more suspension stroke and improves ride quality.
Monotube dampers hold the gas and the shock in one tube, separating the liquid from the gas with a floating piston. The design pushes the damper piston through oil and pushes the oil through chambers through the valves in the piston itself. This design allows the gas to be compressed and react quicker, by compressing slowly over small bumps and more quickly through larger bumps. One incredibly important detail about the Monotube is its ability to be used either way up, unlike most twin tube dampers. Compared to the twin tube design, the Monotube holds more fluid, has better heat dissipation and improves the responsiveness of the damper.
For the best performance on the street or track, the Monotube design is a superior upgrade to the twin tube design.
If you aren’t needing Subaru WRX STI Suspension options designed specifically for heavy track use, Air Suspension is another great choice. While primarily used for street or show cars, many Air Suspension Kits available on the market today are strong enough to withstand light track use as well. While the debate between those that prefer coilovers or air suspension can get pretty heated, the unmatched height adjustability of air makes it a strong WRX STI suspension option in our opinion.
Another thing to consider when modifying your Subaru WRX STI are sway bars. By default, almost all factory cars are tuned with an understeer bias. This makes them easier to drive at their limit, and much safer. For example, a stock Mitsubishi EVO 8 (AWD Turbo) comes factory with a 24mm front sway bar, and a 22mm rear. While there are many upgrades the EVO might need out of the box, the point is upgrading the rear bar should be one of the first mods you do to bring the car to a neutral state. On our EVO 8, we upgraded the rear bar to a 25mm bar and noticed that the bar itself nearly corrected all understeering issues with the car itself. A bar and its size can make the world of difference in handling. Keep in mind when lowering the vehicle it changes your vehicle’s suspension geometry, which can incorrectly preload the sway bars and cause unpredictable handling characteristics, or in an even worse case, damage. To cure this, use adjustable endlinks to correctly preload the sway bar.
A tried and true brand that we recommend is Voodoo13 – you can check out their Subaru components here.
While going fast is fun, how well can you stop at your peak power? This is something that must be considered for every build. Whether you’re building a race car or a street car, how well you are able to brake and how often will make a notable difference. Big brake kits consist of larger calipers with more contact pins in the caliper to hold and compress larger brake pads. With more brake pad surface on the brake rotor, you’ll need less time to push the brake pedal to stop. This also helps stop brake fade, which is a buildup of energy and heat from the brakes that causes them to start slipping after an extended amount of time being used. Larger calipers also help dissipate heat from the braking process, which attributes to less brake fade. Being able to brake efficiently and safely, and in style, makes a Subaru WRX STI Big Brake Kit a key component for your build!
The list of Subaru WRX STI modifications is almost endless; however, we hope this helped give you a good idea of where to start. To learn more about performance upgrades we recommend, including exhausts and tune, check out our full blog here.
08-14 Subaru Impreza WRX STI Coilovers – Kontrol Pro
The Ksport Kontrol Pro Subaru Impreza WRX STI Coilovers provide the ultimate in suspension technology for your vehicle both on the street and at the track. Featuring 36 levels of damping adjustment, Kontrol Pro allows you to easily dial in your system for both handling and comfort. For those seeking a lowered stance as well as improved handling and response at a high value, the Ksport Kontrol Pro Coilover Kit is the perfect choice.The Ksport Kontrol Pro Subaru Impreza WRX STI Coil...(0 reviews)
08-14 Subaru Impreza WRX STI – Gravel Rally Spec GR Coilovers
The Ksport Gravel Rally Subaru Impreza WRX STI Coilovers are built to handle the abuse of the gravel rally racing circuit. The system features a lengthened shock stroke combined with longer springs (ranging from 250mm to 270mm) which allow it to easily absorb uneven road conditions. In addition, the Gravel Rally Coilover Kit also features heavy duty top plates and lower mounts for added strength and durability. Ride height can be adjusted +/- 30mm from OE ride height.The Ksport Gravel Rally Subaru Impreza WRX STI Coi...(0 reviews)
Big Brake Kits
15-18 Subaru WRX STI – Front 3 Piston Big Brake Kit w/ 12 in. Slotted Rotors – Slimline
The new Ksport Slimline Subaru WRX STI Big Brake Kit ensures that you can upgrade to a Big Brake Kit and have it fit most factory wheels, or wheels with very limited brake caliper clearance. The popularity of aggressive fitting wheels on factory body vehicles has never been more popular than it is today. In most cases, aftermarket big brake kits aren’t compatible with this style. Large multi-piston brake calipers just don’t fit within the very limited spacing between the larger brake caliper and the back of the wheel. Ksport has developed the Slimline Caliper with this issue in mind, a design that’s based on the OEM single-side floating piston caliper thickness.
Rotor Diameter: 304 (mm) | 12 (in)
Caliper Type: 3 Piston
Rotor Style: Slotted
Note: Ksport Big Brake kits fit 2WD vehicles only unless otherwise stated.The new Ksport Slimline Subaru WRX STI Big Brake K...(0 reviews)
Air Suspension Kits
08-14 Subaru Impreza WRX STI – Airtech Deluxe Air Suspension
Airtech Deluxe Subaru Impreza WRX STI Air Suspension improves upon our Airtech Basic kit with upgrades to enhance performance and comfort. The Airtech Deluxe system includes everything from our Basic kit as well as two electronic switches for more precise control over manual paddle valves and a wireless remote control. Adjustable lower mounts allow height to be set further down at a point which does not compromise suspension travel so it’s easy to cruise potholed streets at a lowered ride height without you, your suspension components, or sensitive vehicle electronics taking a pounding. All Hoses, wiring, and installation manuals are included with Airtech Deluxe Air Suspension.Airtech Deluxe Subaru Impreza WRX STI Air Suspensi...(0 reviews)