These pistons are produced in small batches in the UK by racing piston specialist Omega. They rely on their engineering expertise aquired through involvement in every genre of racing from the weekend competitor to championship winning F1 and WRC teams. Coupled with a commitment to quality and a strategy of reinvestment in equipment and training ensures that each piston they produce is superior to the competition in every aspect. These EJ20 pistons utilize the V9 and newer crown profile. Forged from heat treated 2618 alloy with a slipper skirt design and a short pin length for an extremely light yet strong piston.Piston kits are priced with rings. Other piston crown profiles and compression ratio options are available on a special order basis so please inquire if the standard options don't meet your needs.
GpN pistons sit higher in the bore to increase compression ratio and are also unmarked on the piston crown to more closely replicate the factory Subaru piston.
Usually ships the next business day.
What is the difference between the 4032 and 2618 alloys commonly used for forged pistons? 4032 is an aluminum alloy with a high silicon and nickel content. It has excellent wear and abrasion resistance and maintains its dimensional integrity over a longer life cycle. Additionally, it has a lower coefficient of thermal expansion allowing pistons to be installed with smaller piston to cylinder clearance resulting in a tighter combustion seal with less noise. These characteristics make it most suitable in high performance street driven applications.
2618 is an aluminum alloy with moderate copper and magnesium content but no slicon. It is a denser alloy with higher thermal conductivity and expansion rate. While these properties require it to be installed with increased piston clearance, it is beneficial in terms of reducing crown temperatures. 2618 has greater strength and ductility making it more forgiving to extreme conditions and detonation. Tensile strength of 2618 is approximately 64ksi vs. around 52ksi for 4032. However, its wear resistance and ring groove dimensional integrity suffers over the long term making it more stuiable for racing applications where shorter life cycles are anticipated and expected.
Can you talk about what makes Omega pistons superior to other piston options? First off Omega is very selective in terms of the quality of the materials they start with. Starting with ultra clean aluminum billets and utlizing advanced forging techniques results in optimal grain structure, surface finish, and strength from the outset. The heat treatment and other surface hardening processes they utilize in combination with very careful skirt profile design and surface finishes maximizes piston life by minimizing wear. Their slipper skirt design, low tension ring package, and the ability to run with no pin offset with very little piston slap keeps frictional losses to a minimum. Ultimately, their pistons weigh less, last longer, run quieter, run with less blow-by and oil consumption, and do this all without sacrificing strength.
Do these pistons use tabbed oil rails? Yes they do. A tabbed oil rail is required on a horizontally opposed engine because it prevents the possibility of oil leakage past the rings on shutdown should the ring gaps align at the bottom of the piston.
What type of piston pin clips are used? Omega uses a factory circlip design for ease of installation.
Which compression ratio should I choose? Higher compression ratios improve off-boost responsiveness and efficiency. However, raising the compression ratio increases the likelihood of engine knock and therefore fuel selection and tuning becomes very critical. Longer duration cams can allow the use of higher compression ratios because of the delayed intake valve closing which reduces the dynamic compression ratio.
Choice of fuel will be the primary determining factor for choosing the optimal compression ratio. Consult your tuner if you are unsure.
