Forged Pistons for Subaru, EJ257 WRX STI, 99.5mm, 8.2:1 (CP Pistons SC7420)
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|
Make |
Subaru |
|
Model |
EJ257 WRX STI |
|
Part Number |
SC7420 |
|
Cylinders |
4 |
|
Bore (in) |
3.917 |
|
Bore (mm) |
99.5 |
|
Size |
STD |
|
Stroke |
79 |
|
Conrod |
130.5 |
|
Comp Height (in) |
1.208 |
|
Comp Height (mm) |
30.7 |
|
Dom/Dish CC |
-21 |
|
Compression Ratio |
8.2 |
|
Weight (Grams) |
392 |
|
Pin (mm) |
23 |
|
Rings |
RS1658-3917-0 |
|
Ring Thickness |
1.2 x 1.2 x 2.0mm |
|
Pin included (Standard) |
905-2500-18CP1S |
|
Upgraded Pin |
905-2500-20CP3S |
|
Ultra Duty Pin |
905-2500-26CP3S |
|
Locks |
905x055 SUB |
CP pistons are compatible with oversized valves and high lift camshafts. CP Pistons represent the highest quality and is engineered for maximum power. Standard features include: Deep valve reliefs accommodate high lift camshafts; Larger valve reliefs for +1mm valve sizes; Custom skirt cam and barrel design; Accumulator grooves; High strength aluminum forgings; High performance rings; Fully CNC machined and balanced to +/- 1 gram; Wrist pins included at no additional cost; Double pin oilers force fed from oil ring groove; Pin lock grooves for easy lock removal; Pin fitting included.
| Product Name | Forged Pistons for Subaru, EJ257 WRX STI, 99.5mm, 8.2:1 (CP Pistons SC7420) |
|---|---|
| Brands | CP Carrillo |
| Engine | EJ257 WRX STI |
| Make | Subaru |
Delivery & Freight
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What information do I need to match these pistons to my engine?
You need the engine code, bore size, stroke, rod length, pin diameter and target compression ratio. These determine the correct piston compression height and crown design.
How should ring gaps be set for these pistons?
Ring gaps must be set by your engine builder based on fuel type, boost level and the intended rpm range. Forced-induction engines usually require larger gaps.
Are forged pistons suitable for street engines?
Yes. Forged pistons handle detonation and high cylinder pressure better than cast units. Your builder should set the piston-to-bore clearance to suit your application.
What is the recommended bore clearance for the SC7420 pistons?
The recommended bore clearance for the SC7420 pistons in an EJ257 engine typically ranges from 0.0015" to 0.0025". However, it's crucial to consult with your engine builder to determine the best clearance based on your specific application and intended power levels.
What compression ratio can I expect with the SC7420 pistons?
The SC7420 pistons have a compression ratio of 8.2:1 when used with a standard EJ257 engine configuration. This ratio is suitable for applications requiring lower compression, such as those running higher boost levels.
Are the SC7420 pistons compatible with aftermarket camshafts?
Yes, the SC7420 pistons feature deep valve reliefs designed to accommodate high lift camshafts and oversized valves. This makes them suitable for performance builds that utilise upgraded camshaft profiles.
What type of wrist pins are included with the SC7420 pistons?
The SC7420 pistons come standard with 23mm wrist pins. You also have the option to upgrade to heavier-duty wrist pins if your application demands additional strength.
What machining is required for the SC7420 pistons before installation?
Before installation, ensure that the cylinder bores are properly honed to match the piston size and that the ring gaps are set according to your engine's specifications. It's also advisable to balance the rotating assembly for optimal performance.
