What is the purpose of the dish in these pistons?

The dish in the piston crown helps to reduce the compression ratio. For this specific set, the dish, combined with the bore size and standard stroke, results in an 8.5:1 compression ratio, which is often desirable for boosted applications where lower compression helps prevent detonation.

What does the +.05mm bore size mean for installation?

This means the piston is 0.05mm larger in diameter than the standard bore size. It's intended for use in an engine block where the cylinders have been precisely machined (honed) to this exact 99.55mm diameter. This is common when rebuilding an engine to ensure proper piston-to-wall clearance.

Are these pistons suitable for high-performance or racing applications?

Yes, these pistons are built with 2618 alloy forgings and feature design elements like precise ring lands and skirt profiles that are favored by professional engine builders and tuners for demanding, high-performance applications.

Specifications

Brand: Manley Performance
Part #: 612001C-4
UPC: 807298084374

Manley 04+ Subaru WRX STi (EJ257) STD Stroke 99.55mm +.05mm Bore 8.5:1 Dish Piston and Ring Set

Name: Manley 04+ Subaru WRX STi (EJ257) STD Stroke 99.55mm +.05mm Bore 8.5:1 Dish Piston and Ring Set
Brand: Manley Performance
SKU: manley-performance-manley-04-subaru-wrx-sti-ej257-std-stroke-99-55mm-05mm-bore-8-t14-304860
Price: 758.81 USD
Availability: InStock

$758.81

Only 1 left in stock

Manley 04+ Subaru WRX STi (EJ257) STD Stroke 99.55mm +.05mm Bore 8.5:1 Dish Piston and Ring Set. Forged from 2618 alloy for superior strength.

Key Features

Fits 2004 and later Subaru WRX STI with EJ257 engine.
Forged from domestic 2618 alloy for superior strength and performance.
99.55mm bore size, which is +.05mm over standard, with a dish design for an 8.5:1 compression ratio.
Features Manley's proven cam and barrel skirt profiles for smooth operation and reduced cylinder wall wear.
Exacting standards for ring lands and grooves ensure enhanced ring seal and more power.
Includes premium chrome moly wrist pins for added durability.

⚠️ CA WARNING: This product can expose you to chemicals known to the State of California to cause cancer and/or birth defects or other reproductive harm. Learn more

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About this part

Product Details

Built from domestic 2618 alloy forgings, these Manley pistons are designed for serious engine builds in your 2004 and later Subaru WRX STI with the EJ257 engine. They feature a dish design that results in an 8.5:1 compression ratio when used with the standard stroke and a 99.55mm bore. This specific sizing is a +.05mm overbore, meaning it's designed to be used in a cylinder that has been honed to that precise measurement, often after a previous rebuild or to achieve a specific clearance.

Manley's signature cam and barrel skirt profiles are a key feature here. They're shaped to help the piston move smoothly within the cylinder, reducing friction and wear on the cylinder walls while still allowing the engine to make substantial power. The ring lands and grooves are machined to exacting standards, which is crucial for getting a good seal from your piston rings. A solid ring seal means better compression, improved oil control, and ultimately, more power from your engine. These pistons also come with premium chrome moly wrist pins, known for their strength and durability.

When you're building an engine that needs to perform reliably under demanding conditions, the details matter. Manley's unique fixturing process allows them to machine the piston skirt and cut the ring grooves in a single operation. This ensures the ring grooves are perfectly square to the piston skirt, which is essential for optimal ring seal and performance. These pistons are a popular choice among professional engine builders and tuners who need dependable components for high-performance applications.