What is the benefit of the 8.5:1 compression ratio dish piston?

The dish top on these pistons lowers the compression ratio to 8.5:1. This is beneficial for turbocharged or supercharged engines, as it helps to prevent detonation or pre-ignition under boost by reducing the pressure and temperature in the combustion chamber.

Are these pistons suitable for all engine builds?

These pistons are designed for performance applications in 2004+ Subaru WRX and STI models, particularly those that are turbocharged and may require a lower compression ratio for boost. They are forged from 2618 alloy for strength. It's always recommended to consult with your engine builder to ensure they are the right choice for your specific build goals.

What does the +.05mm size mean for my engine?

The +.05mm size indicates that these pistons are slightly larger than the standard bore size. This is typically used when an engine block has been bored out to a larger size during a rebuild. It's important to ensure your engine block has been machined to match this specific bore size for a proper fit.

Specifications

Brand: Manley Performance
Part #: 632201C-4
UPC: 807298088013

Manley 04+ Subaru WRX/STI EH257 99.55mm Bore +.05mm Size 8.5:1 Dish Piston Set

Name: Manley 04+ Subaru WRX/STI EH257 99.55mm Bore +.05mm Size 8.5:1 Dish Piston Set
Brand: Manley Performance
SKU: manley-performance-manley-04-subaru-wrx-sti-eh257-99-55mm-bore-05mm-size-8-5-1-d-t14-4339033
Price: 827.84 USD
Availability: BackOrder

$827.84

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Manley 04+ Subaru WRX/STI EH257 99.55mm Bore +.05mm Size 8.5:1 Dish Piston Set. Forged from 2618 alloy for superior strength.

Key Features

Fits 2004 and later Subaru WRX and STI models.
Forged from domestic 2618 alloy for superior strength and performance.
99.55mm bore size, which is +.05mm over standard.
Dish top piston design results in an 8.5:1 compression ratio.
Features proven cam and barrel skirt profiles for smooth operation and reduced cylinder wall wear.
Exacting standards for ring lands and grooves enhance ring seal and power output.

These pistons are designed for 2004 and later Subaru WRX and STI models. Please verify compatibility with your specific engine build and requirements.

⚠️ 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

Starting with the 2618 alloy forgings, these Manley pistons are built for serious performance in your 2004 and later Subaru WRX or STI. The 99.55mm bore size, which is +.05mm over standard, is designed to work with specific engine builds where a slight increase in displacement is desired. These pistons feature a dish top that results in a compression ratio of 8.5:1, making them suitable for boosted applications where managing detonation is key.

Manley uses proven cam and barrel skirt profiles that help these pistons move smoothly within the cylinder walls, reducing wear and noise while still generating substantial power. The ring lands and grooves are machined to exacting standards, which is crucial for achieving a solid seal with your piston rings. This precise machining helps ensure you get the most power out of every combustion cycle. The included wrist pins are made from Chrome Moly, offering good durability for most performance builds.

When you're rebuilding your engine, especially for performance tuning, the details matter. Manley's unique fixturing process allows them to machine the skirt and the ring grooves in one operation. This ensures the ring grooves are perfectly square to the piston skirt, which is vital for proper ring function and sealing under high pressure. These pistons are not CARB approved and cannot be shipped to California.