When you have a turbocharged engine, most manufacturers only use 80% of the full capability of the turbo.
They do this to make the engine more reliable and last longer. But this is something an enthusiast has to put aside, whether they realize it or not.
Since the manufacturer left so much on the table, some exhaust work and a tune unlock a considerable amount of power. But what do you do when you want even more power? The next step is a larger turbo.
When it comes to selecting a turbo, you will find out that there may be hundreds of different turbos available, but only some are listed as fitting your car.
We're going to use a 2013 Subaru WRX and STi as an example. Your favorite online retailer lists 40+ turbos for the STi, but only 6 for the WRX. Why? They're almost the same motor.
Even though the motors are very similar, the exhaust systems identical, and the intakes the same, they have very different intake manifolds and intercoolers. The WRX has a modern plastic intake manifold and cheaper plastic and aluminum intercooler.
The STi has the same aluminum intake manifold it has had since 2004 and a much larger all aluminum intercooler. The intercoolers and manifolds have different locations for the throttle body and the connections to the intercooler, making them incompatible.
The STi style manifold has been around since 2004 and is even compatible with the first WRX's in 2002. This has given the aftermarket community 11 years to come up with stock replacement turbos and 11 years of vehicles to support their products. Even though the only real difference between the WRX turbo and the STi turbo is the compressor cover (other than power capability), not much attention has been given to the WRX community. There are only a handful of turbos to choose from.
- One may think that the only way a WRX can utilize STi style turbos would be to swap to an STi style intake manifold, this is not the best decision.
The plastic manifold is actually a better material. The plastic is smoother for better airflow and will not heat soak like the aluminum one will. Not to mention the swap is not as simple as just the manifold. You would also need TGV's, Fuel Rails, and a new Intercooler. 
A very commonly overlooked way to utilize an STi style turbo on a WRX is to get a GrimmSpeed or Process West intercooler. Not only do companies offer an incredible product, they also offer an optional adapter hose that will allow you to use an STi style turbo with the plastic manifold. This is the simplest and cheapest way to expand the available turbos for your vehicle.
Get the power gains you want while also having a car that you can drive everyday. Choose the turbo wisely, also choose a shop that demonstrates doing it right.
