CP Pistons & Piston Kits

The best pistons for a WRX or STI engine build are forged pistons matched to your bore size and compression ratio. CP Pistons offers forged piston sets for Subaru EJ255 and EJ257 turbo engines as well as FA20 engines in the BRZ, covering bore sizes from 86mm to 100mm. Forged pistons handle the heat and cylinder pressure of boosted builds far better than stock cast pistons — one of the first internal upgrades for a serious EJ or FA build.

Pistons transfer combustion force through the connecting rods to the crankshaft. In a turbocharged Subaru that force is enormous, and stock cast pistons are a known weak point once boost rises — forged pistons are denser and more ductile, resisting cracking and ring-land failure under high cylinder pressure. When shopping, the two numbers that matter most are bore size and compression ratio. Options here include 99.5mm and 100mm for EJ255/EJ257 blocks and 86mm for the FA20, with ratios from 8.2:1 to 10.5:1 — choose based on fuel, boost level, and your tuner’s recommendation.

Pair new pistons with fresh piston rings and connecting rods for a complete rotating assembly refresh, and always confirm your exact bore size with your machine shop before ordering.

CP Pistons, the forged-piston brand in the CP-Carrillo family, is a fixture in turbocharged Subaru builds. The range shows why: EJ255/EJ257 sets in 99.5mm and 100mm bores at 8.2:1 and 10:1 compression ratios, plus FA20 sets in 86mm at 10.0:1 and 10.5:1 for the BRZ. CP’s reputation is built on forged pistons engineered for forced-induction applications, where ring seal and strength under boost matter most.

JE Pistons is another forged-piston specialist with a long history in racing applications, from street performance to full race engines — its Subaru-specific forgings are a common alternative in EJ builds.

Wiseco is known for forged pistons across powersports and automotive performance, with application-specific forgings for popular turbo platforms — a solid brand to compare when spec’ing a build.

Mahle is a longtime OEM engine-components supplier whose motorsport division produces performance pistons with a distinctly OE-refined character.

Two strong starting points: the CP Piston Set 99.5mm Bore 10:1 CR for 2006-2014 WRX / 2004-2019 STI covers the classic EJ25 turbo build, and the CP Pistons FA20 Piston and Ring Set 86mm Bore 10.0:1 for 2013-2020 BRZ suits the FA20. Our product highlight on the 2015+ FA engine WRX is useful FA-platform background.

Do I need a tune after installing forged pistons?

If your new pistons change the compression ratio from stock, a tune is strongly recommended so fueling and timing match. Even with a stock-ratio set, most boosted builds get retuned anyway.

What bore size and compression ratio should I choose?

Match the bore to your machine work — confirm with your machine shop before ordering. Compression ratio depends on fuel and boost: lower ratios (like 8.2:1) suit high-boost pump-gas builds, higher ratios suit moderate boost. Your tuner’s input matters here.

Are piston rings included?

Some sets include rings and some are piston-only — check the individual product page. Replacement ring sets are also available separately in our piston rings collection.

Is installing pistons a DIY job?

Piston replacement is engine-out work involving clearance checks and cylinder honing — most buyers have a machine shop or experienced builder handle the short-block assembly.