Your Guide to Performance Enhancements for Subaru

close-up of 2 subaru cars

Take a rally-bred 4-wheel drivetrain, bolt on a high revving turbocharged flat-four, stick some grippy tyres and you’ve got the basic ingredients for raw unadulterated motoring fun. The Subaru WRX STI is the direct descendant of the Impreza WRC, the car that annihilated every car in the World Rally Championship in the 1990s. It’s here that Subaru achieved all their racing glory. And translated it into a performance car that anybody could own.  

The WRX STI is the car that Aussies still love to tune, while waiting for the promised 2022 replacement. Until we all get to see what the stock 400 bhp (on paper, anyway) offers, drivers can squeeze more out of the 300 horses in the outgoing model with high-spec performance Subaru parts. The 2.5-litre boxer still has a lot to give, albeit with some minor tweaks.  

If you’re unprepared for the sheer power from the legendary EJ25 engine and boost from the high-spooling turbo, Subaru offers the milder and lower displacement FA20 in the standard WRX and Forester XT, and ditches the turbo in the BRZ. All engines and engine variants are pokey, bring on power from down low, and pull all the way to the redline. 

Subaru Performance Enhancements 

close-up of subaru engine sti

Tuning the WRX or STi is like tuning any other car, except here you have more to play with. Basic mods start with the exterior. These won’t affect speed as much as overall handling. And you get more curves to boxy outline. Owners go for lighter and bigger alloys, coupled with beefier brakes and callipers with more bite. Don some performance spec low-profile tyres to shed a few millimetres. You get more grip (not that that was lacking), better feedback from the steering wheel, less body roll in corners, and shorter stopping distances. To smooth out drag and literally glue the car to the road, Subaru offers OEM styling kits, that consist of front, side and rear under spoilers.  

Under the Bonnet 

Real performance enhancements begin with the mechanicals. You can be gentle and use mild upgrades or go for the most available power. Before touching anything, it is recommended to do an ECU tune to remap stock parameters. Remaps make changes to turbo boost levels, delete rev and speed limiters, improve timing and more. Look for reputed tuning software and get the work done by a tuning specialist.  

Once you’ve remapped the ECU, it’s time to improve airflow. Subaru parts used here include a high flow intake to feed the engine with more air. A cat-back exhaust leading from a modified exhaust manifold, revised wastegate and a downpipe with a converter delete will get the air out faster, resonate more of the characteristic Subaru rumble and relieve back pressure. To regulate engine temperatures with pressure increases, a bigger aftermarket intercooler should level things out.  

Getting Serious 

Moving things up a notch, you can spend on a bigger turbo that won’t go out of puff as the revs build to the redline. The size of the turbo will determine the rev range at which it kicks in. A bigger turbo will have more top-end grunt, but will pick up at higher revs than a smaller turbo, so choose wisely. Complete turbo kits, including modified wastegates, downpipes and connecting clamps and flanges are available for your Subaru from reputed turbo specialists.  

More air means more fuel. Changes to fuelling include a fuel pump able to feed bigger fuel injectors. The stock injectors won’t provide enough pressure to compensate for the increase in air. Going for injectors at or above 1000cc will get you the right mix. Mods up to here can uncover up to 100 bhp, depending on what you install and what you leave out. To get all that power down to wheels it is recommended to upgrade the clutch, especially the stock clutch in WRX. The STI can handle the increase in torque but starts to slip higher in the powerband. Clutches with stronger pressure plates can handle the increased friction.  

Going Ballistic 

close-up of tuned subaru sti

With so much added power, the stock internals start to struggle. There have been instances of cracked pistons, fried piston rings, or twisted conrods. You’ll also notice noise that wasn’t there. The internals in STi can handle the power increase to certain levels, but even these have their limits. Go for a forged performance piston and conrod combo to get the engine spinning faster. They’ll last the higher pressure and temperatures from previous mods, and bigger bangs. If money isn’t an issue, then a matching forged crank can bring your car close to 500 bhp. If that isn’t enough, a stroker kit can increase displacement by 10-15 per cent, depending on the size of bore you choose. These are serious mods that need to be paired carefully to get the right balance and the performance figures you’re after. 

Most mods here relate to the EJ257 in the WRX STI. This after all is the most modified Subaru. A detuned and older version of the engine also sits in the engine bay of previous-gen Libertys. Parts and kits for other engines, particularly the FA20 in the WRX with the turbo fitted, and the naturally aspirated engine in the BRZ are also widely available.