The Subaru WRX STI has been the staple of DirtFish’s teaching operations since our inception 10 years ago. Our current fleet of the newest generation STI is the fastest of our regular offerings, and provide students with the perfect platform for learning how to drive an all-wheel-drive car in the dirt.
These cars are far from stock however, and in this article we will go over everything that needs to happen to a DirtFish school STI to make it rally-ready and reliable for students.
Drivetrain
Each DirtFish STI has a fully built EJ25 motor. Bearings, rods, pistons and more have all been replaced to help the cars hold up better to the constant high-revving and boost that the cars go through for hours at a time, multiple times a week.
The turbo is also out of the street cars, pushing the power output to roughly 280 horsepower, and allowing students to learn the powerband of a turbo motor, and the importance of keeping the boost going.
In-house clearances and specs are used for the motor to find the perfect blend of longevity and performance for use in the fleet. The set-up and tunes have been perfected on the dyno to find the right mix of all the factors, and to get past a lot of the OEM and emissions related setbacks of the roadgoing model.
The motor pairs to a standard six-speed manual transmission that’s in the STI from factory. The TY85 transmission is able to stand up to the power quite well, and with an Exedy clutch installed, it also stands up to the students who are learning manual for the first time.
An OEM limited-slip differential is still utilized to help drive power to the wheels, and specifically to keep it flowing relatively evenly rather than taking the path of least resistance to whichever wheel has the least traction.
Various other drivetrain bushings have been added to stiffen and strengthen the drivetrain to help handle all of the jouncing the cars receive on a daily basis.
Topping it all off is a high flow exhaust for that famous rally car engine sound.
Interior
The interior of each car is completely stripped down to allow for a multi-point roll cage, as well as to lighten the cars up a little.
Steering wheels, front seats, safety belts, and more are all removed and replaced with the race-spec equivalent for both safety and to make the experience more like a stage-prepped car.
Infotainment and creature comforts are stripped as well to make each car as light as safely possible.
The cars also have a high-tech intercom system integrated into the helmets to allow student and instructors to communicate clearly over the sounds of racing.
Brakes, wheels, and suspension
The STI fleet is equipped with a high power braking system to allow drivers to brake as late as possible. This system is from Subaru, and is necessary to fit under the 15 inch Method Race Wheels.
The brake booster has been removed from each car to allow for fully manual brakes. Smaller brake calipers have been installed to allow for clearance inside the rally-spec wheels. The front has four-piston calipers, while the rear has two-piston calipers. Hawk Performance brake pads are utilized for an extra bit of performance as well.
It’s not a rally car without a hydraulic handbrake, and it’s not a driving school car without an instructor brake in case of emergency. It’s the same case for the DirtFish STI fleet, allowing drivers to kick the rear-end out and whip around hairpins, while allowing instructors to take control if the situation gets out of hand.
Flying at high speeds over the rough rally surfaces would not be an ideal situation for the street suspension these cars come with from the factory and in order to stand up to the changing surfaces of DirtFish’s courses each car has Reiger Rally Suspension increasing travel and providing increased durability.
A Bilstein motorsports shock is also used on the rear of the car. This set up allows for rebuilding when a component fails, whereas the OEM setup would just need to be fully replaced.
A custom-built in-house strengthening kit is added to the rear subframe to improve rigidity and handling.
Custom rear wheel scrapers are also installed to keep any dirt or mud from piling up on the inside. This could cause issues both in interfering with braking areas, as well as throwing wheels off balance and making the car harder to control.
Making contact with the ground is a set of Hoosier Gravel Rally tires, specifically designed to stand up to this style of driving.
Underbody
A great deal of effort has gone into protecting the underside of these cars from a constant barrage of high-speed gravel pelting it.
The wheel wells are all lined with ultra-high-molecular-weight polyethylene (UHMW), a strong plastic-like material known for being resistant to abrasion. The underbody is lined with a similar material, high-density polyethylene (HDPE). This also helps keep dirt out of many mechanical parts making for easier surface, and less chance of early failure.
On top of this each car has a ¼-inch aluminium skip-plate to protect against the front of the car bottoming out hard on rough surface. Body protection is topped off with polyurethane mudflaps to help prevent gravel and other debris from reaching the underbody in the first place.
The sum of all these parts is a reliably high-performance car capable of teaching students anything from basic car control all the way up to the most advanced rallying techniques.
