CP FORGED PISTON WRX STI / EJ257
CP Pistons is one of the most trusted names in the industry, and for good reason. Their extensive shelf catalog provides the user with many of the options that you'd normally be resigned to going to a custom piston for. Their standard offering already includes Dual Pin Oilers - providing double the amount of oil to the wrist pin, radiused valve reliefs, and the pin fitting final hone on the wrist pin bore. They even include an Accumulator Groove as a standard option. This provides a small pocket for the combustion gasses to collect after the first ring, reducing ring flutter and providing a better seal allowing more downward force on the piston A.K.A. - make more power. All pistons come balanced within one gram, include pin lock grooves and wrist pins at no additional charge.
* PLEASE NOTE NOT ALL PISTON ARE STOCKED ON THE SHELF AND WILL HAVE TO BE ORDERED IN*
CP Standard Shelf Pistons
- 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
- USA Made
Pistons come with wrist pins, pin fitted, and locks (except for Subaru).
ANTI DETONATION GROOVES (CONTACT REDUCTION GROOVES)
Also know as contact reduction grooves, which limit the piston/cylinder contact during high temperature and high RPM. These grooves also protect the top ring by disrupting detonation waves.
V-shaped groove machined in the 2nd ring land that adds to the volume between the top and second ring. This groove accumulates residual gasses from combustion which alleviates top ring flutter and premature second ring wear, improving ring seal.
DOUBLE PIN OILERS
Double Pin Oilers (opposed to single pin oilers), in conjunction with our annular reservoir, can add twice the amount of oil from the cylinder wall to the wristpin bore. This is a standard option on any piston that receives forced pin oiling.
Broaches are horizontal slots in the pinbore designed to allow oil to enter between the wristpin and pinbore. Broaches are also used to accommodate the wristpin shape under compression, as it can become somewhat oval and needs room in order to alleviate galling.
The pin bore is precision honed to attain an exact pin clearance. Depending on the application clearances typically range from .0003 to as much as .003 between the wristpin and pin bore.