STI Transmission Swap Guide for the 2022+ WRX

What the swap actually requires

The single most common mistake is budgeting for a transmission and discovering you bought half a project. Swap packages typically supply the adaptation hardware: shift linkage, seals, gaskets and mounts. That is the part that makes the conversion possible, not the part that makes it complete. What you still have to source separately: the transmission itself, a driveshaft, axles, a clutch, a flywheel, a slave cylinder, a shift knob, and a rear differential. That last item catches people out. The STI 6-speed requires a matching R180 rear differential, which means you are not just changing the gearbox - you are changing the rear of the drivetrain to match it, along with the driveshaft length and axle configuration that go with the combination. So the real parts list spans the entire length of the car, and the specific list depends on which transmission you source, which clutch style it uses, and what differential and axles pair with it. This is why swap specialists build customised kits rather than selling one part number. Add labor. This is a gearbox out, differential out, driveshaft and axle job with custom fitment work on a chassis that has not had this done a thousand times. If you are not doing it yourself, the labor line is significant.

Supporting parts for a swapped car

The financial reality

Set this against the rest of the platform to see it clearly. A 300whp ethanol build costs roughly $3,400 in parts and sits inside every factory limit. A 400whp build runs roughly $8,000 to $10,000 in parts and $10,000 to $14,000 all in. The transmission swap is a further five-figure conversation on top of that once you count transmission, differential, driveshaft, axles, clutch, flywheel and the labor to make it all work on a chassis that needs custom adaptation. So the swap is not a step within a build. It is a decision that roughly doubles what the project has already cost. The honest alternative that nobody wants to hear: cap the build. A car making 350 lb-ft with an upgraded turbo, tuned properly and driven with mechanical sympathy, is genuinely fast and stays inside what the factory drivetrain was designed for. You give up the biggest peak numbers and you keep your money and your gearbox. The cars that end up needing this swap are usually cars whose owners never made a deliberate decision about where to stop. They added a turbo because the stock one ran out, then a fuel system because the turbo needed it, then discovered the transmission was next. Deciding your ceiling before you start is what prevents that sequence.

The verdict

Do this swap if you have already built an engine that makes meaningfully more than the factory gearbox's comfortable torque range, you intend to keep using that power, and you have budgeted for the differential, driveshaft, axles and labor rather than just the transmission. Do not do it as a preemptive strengthening measure on a stock-turbo car. For a stock-turbo goal, price the complete swap against the torque target, use case, condition, and risk tolerance; do not assume either that the factory gearbox is guaranteed safe or that extra capacity can never be useful. And if you are reading this because you are planning a big-power VB from scratch, the useful takeaway is to price the transmission into the plan from the beginning. A 400whp build that discovers the gearbox question halfway through is a project that stalls. One that budgeted for it is just an expensive car that works.