CP Pistons SC70457-4 K20A/A2/A3 Forged Piston and Ring Set 87mm Bore 9.6:1 2618 Aluminum Made in USA

SC70457-4 is a complete four-piston forged set engineered specifically for the Honda/Acura K20A, K20A2, and K20A3 engine family. CP Pistons machines every unit at their Irvine, California facility from 2618 forged aluminum, a high-strength aerospace-grade alloy chosen for its resilience under thermal and mechanical load. At 87mm bore (+1.0mm over the stock 86mm K20 bore) and a 9.6:1 flat-top compression ratio, this set is designed for street performance, time attack, and mild-to-aggressive forced-induction builds where factory cast pistons are not an option.

Made in USA. Manufactured at CP-Carrillo, 1902 McGaw Ave, Irvine, CA. Every piston in this set is CNC machined, balanced to within plus or minus 1 gram, and inspected in a climate-controlled quality department before shipment.

Key Specifications

What's Included

SC70457-4 ships as a complete, ready-to-install piston set. Every component is included at no additional charge:

• 4x Forged pistons (SC70457), 87mm bore, 9.6:1 flat top, 2618 aluminum
• 4x Ring sets (CPN-3425): 1.0mm top ring, 1.2mm second ring, 2.8mm oil ring, one set per piston
• 4x Wrist pins (866-2250-20CP1C), 22mm diameter, floating/forced style
• 4x Wrist pin locks (866x063 SWL)
• Pin fitting service: CP-Carrillo performs a final hone of the wrist pin bore to achieve proper clearance before shipment, included at no charge

Not included: connecting rods, head gasket, gas ports (custom order option), skirt or ceramic coating (custom order option), upgraded heavy-duty wrist pins (custom order option).

Construction and Design Features

2618 forged aluminum: This alloy offers higher tensile strength and better fatigue resistance than the 4032 alloy used in many OEM and economy piston lines. 2618 requires slightly more piston-to-wall clearance and runs a slightly larger thermal expansion coefficient, which is standard for a high-performance forging.

Dedicated forging: The SC70457 blank is not a universal slug resized to fit. CP Pistons engineers a dedicated forging geometry for each K20 bore and compression ratio target, which allows a tighter, more accurate skirt cam profile and barrel shape compared to cut-down blanks.

Accumulator grooves: A shallow groove machined between the top land and the first ring groove disrupts detonation pressure waves before they reach the top ring face. This extends ring life under high-load, high-RPM, or boosted conditions.

Dual forced pin oilers: Two oil delivery holes are force-fed from the oil ring groove, delivering twice the lubrication to the wrist pin interface compared to single-oiler designs. The result is reduced pin wear at sustained high RPM.

Deep valve reliefs: The flat-top design incorporates generous valve pockets, compatible with stock lift cams and aftermarket cams running up to +1mm oversized valves. Build clearance should always be confirmed at final assembly.

CNC machined and balanced: Every piston is machined on CNC equipment and hand-inspected to plus or minus 1 gram across the set. Tight weight matching reduces vibration and rotating assembly imbalance without additional balancing work at the machine shop.

Vehicle and Engine Fitment

This piston set is sized for the K20A, K20A2, and K20A3 engine architecture: 86mm stroke, 139mm rod length, 22mm wrist pin. Confirm bore sizing with a bore gauge before ordering. A cylinder bore must be machined to the correct 87mm diameter with proper surface finish before installation.

Bore Size Variants and Related Part Numbers

Lower compression (9.0:1 dish top for forced induction): SC7040 series, 86mm through 89mm bore.

High compression (11.5:1 for N/A race builds): SC7140 series, 86mm through 90mm bore. Not suitable for forced induction.

Installation Notes

Installing forged pistons requires full engine disassembly: removal of the cylinder head, oil pan, connecting rods, and crankshaft (or at minimum the rods). This is a performance engine rebuild, not a bolt-on modification. Proper cylinder machining, surface finish, ring gap filing, piston-to-wall clearance measurement, and torque-to-yield fastener replacement are all part of a correct installation. Work should be performed by a machinist or engine builder experienced with high-performance applications.

Under the Magnuson-Moss Warranty Act, installing aftermarket internal engine components does not automatically void an entire factory powertrain warranty. However, a K20 engine rebuild of this nature is by definition a performance modification involving replacement of factory components. Any remaining factory powertrain coverage should be evaluated before proceeding.

Frequently Asked Questions

What is the exact bore size for SC70457-4?
The bore diameter is 87mm (3.425 inches), +1.0mm over the stock K20 bore of 86mm. Your machine shop must bore and hone the block to 87mm with the correct surface finish before installation.

What piston-to-wall clearance is required for these forged pistons?
For 2618 forged aluminum in a street/performance K20 build, clearances between 0.0025 and 0.0035 inches (0.064 to 0.089mm) are typical. 2618 alloy expands more than 4032, so clearance is slightly greater than you would set for a 4032-based piston. Confirm with CP-Carrillo technical support for your specific application.

What are the recommended ring end gaps for this kit?
For naturally aspirated K20 builds at 87mm bore, a starting point is approximately 0.016 to 0.018 inches for the top ring and 0.016 to 0.018 inches for the second ring. Boosted applications typically run wider top ring gaps of 0.020 to 0.024 inches. File rings to spec before installation; never assume out-of-box gaps are correct.

Does this kit work with a K24 block using a K20 head?
No. These pistons are dimensioned for the K20 stroke (86mm) and rod length (139mm). They are not designed for use in a K24 long block with its 99mm stroke. K24 hybrid builds require pistons sized specifically for K24 geometry.

Is this set compatible with a turbo or supercharged K20 build?
Yes. The 9.6:1 compression ratio is workable on mild boost with proper fueling and ignition tuning. For high-boost applications over approximately 15 psi on pump gasoline, the 9.0:1 dish-top SC7040 series is a more conservative choice. The 9.6:1 flat top is popular for street builds running modest boost on E85 or high-octane pump fuel.

Do these pistons come with a skirt coating?
No coating is applied to this shelf SKU. Optional moly skirt coating, DLC coating, and ceramic top coating are available through CP-Carrillo on custom order.

What compression ratio change can I expect versus stock K20A3 pistons?
The stock K20A3 runs approximately 9.8:1 compression at the stock 86mm bore. This set targets 9.6:1 at 87mm bore. Actual compression ratio in your build depends on combustion chamber volume, head gasket thickness, and deck height. Always calculate final compression ratio using measured values from your specific parts.

Where are CP Pistons manufactured?
All CP shelf and custom pistons are manufactured at CP-Carrillo's facility at 1902 McGaw Ave, Irvine, CA 92705. Made in USA.

Warranty

CP-Carrillo guarantees the quality of the aluminum alloy, the forging process, the heat treatment, and the dimensional accuracy of every piston. This guarantee covers material and manufacturing defects only. CP-Carrillo products are sold without warranty of merchantability or fitness for a particular purpose, express or implied.

California Proposition 65 Warning

WARNING: This product may contain chemicals known to the State of California to cause cancer, birth defects, or other reproductive harm. For more information, visit www.P65Warnings.ca.gov.

This product is not CARB-exempt and is not legal for sale or use on public roads in California.