CP Forged Pistons Subaru WRX STi EJ257 2.5L 99.75mm +0.25mm -21 cc 8.2:1

This piston is designed to be used with a standard-stroke Crank in an EJ257 block with a standard-length connecting rod. This combination works out to a 2.5L depending on bore size.

Compression Ratio:
This piston maintains the standard compression ratio.

Bore Size:
The bore size of this piston is larger than stock. That means the cylinder will need to be bored to match these pistons. We recommend not having the block bored till the machine shop has the pistons in-hand. The block should be bored to YOUR pistons.

File to Fit Rings:
These pistons come with file-to-fit rings. This means the rings come slightly-long, and MUST be filed to the desired ring-gap for your application. This ring gap can vary depending on what your engine will be used for. For example, a 1000hp drag-only application will have a much different ring gap than a 300hp daily driven engine. Consult with your engine builder before filing your rings, and do not install the rings without filing them.

These pistons, like many aftermarket pistons, are made of 2618 alloy. 2618 is a strong, durable, forged aluminum alloy that can withstand a large amount of abuse in race applications.

Tools:
If you are installing these pistons yourself, there are some tools you will need to install them in your engine correctly. We can help supply you with these tools if you don't already have them. At the very minimum you will need a quality torque wrench and a ring compressor. You should also get a quality bolt-stretch gauge to properly torque your rod bolts. Please see the supporting mods section of this page to add these tools to your shopping cart.
CP Standard Shelf Pistons
Features
Dedicated forgings
Balanced to + or 1 gram
Wrist pins provided at no cost
Pin fitting provided at no cost
Accumulator Grooves
Dual forced pin oilers
Pick lock grooves
Fully CNC machined