JE Pistons 297173 FSR Piston Kit 87mm 11.5:1 for 1996-1999 BMW M3 E36 S52B32

Vehicle Fitment

• 1996-1999 BMW M3 (E36 Coupe, Sedan, Convertible - S52B32US 3.2L Inline-6 24V, RWD)
• 1998-2000 BMW Z3 M Roadster / M Coupe (E36/7, E36/8 - S52B32US 3.2L Inline-6 24V, RWD)

Fitment Notes

• Fits the North American (USA/Canada) S52B32US engine only. Does not fit the European S50B32 engine used in non-US E36 M3 models.
• This is an oversize piston at 87.00 mm (+0.60 mm / +0.024 in. over stock). Professional cylinder boring and honing to the correct piston-to-wall clearance is required prior to installation.
• Does not fit the 1995 BMW M3 (E36) US model, which used the S50B30US 3.0L engine.
• Does not fit any non-M E36 3 Series models (320i, 323i, 325i, 328i), which use M52 or M50 engines.
• Compression ratio of 11.5:1 is calculated assuming a 0.069 in. head gasket thickness and 34 cc combustion chamber volume.
• Single replacement piston available under part number 297173S. This listing is for the complete 6-cylinder set.

Features

• Forged from 2618 T6 high-tensile aluminum alloy - the ideal material for high-compression, high-revving naturally aspirated engines as well as forced induction or nitrous applications.
• Asymmetrical FSR (Forged Side Relief) forging technology reduces skirt mass and friction on the minor thrust side while maintaining a larger, more rigid skirt surface on the major thrust side for superior strength and stability.
• Crown geometry requires no deburring or preparation after machining - ready to install right out of the box.
• Inverted dome / dish crown design engineered specifically for the S52B32US combustion chamber to achieve the target 11.5:1 compression ratio with precise -9.90 cc dish volume.
• Floating wrist pin design (22 mm diameter) with included wire-lock retainers ensures smooth pin movement and reduces side loading on the pin bosses under high-rpm operation.
• Chamfered wall construction provides additional oil retention and improved skirt contact during cold starts and initial break-in.
• All pistons balanced within one gram of each other to minimize rotational imbalance and promote smooth engine operation at high RPM.
• Radiused valve reliefs provide precise clearance to S52B32 camshaft valve lift profiles (10.2 mm intake / 10.2 mm exhaust) without sacrificing combustion chamber volume.
• Engineered, forged, and fully CNC-machined 100% in the USA to millionths-of-an-inch tolerances.

Specifications

• Part Number: 297173
• Engine Application: BMW S52B32US 3.2L Inline-6 24V
• Bore Diameter: 3.425 in. (87.00 mm) - +0.60 mm / +0.024 in. Oversize
• Compression Ratio: 11.50:1 (assumes 0.069 in. head gasket, 34 cc chamber)
• Piston Head Type: Inverted Dome / Dish
• Dome Volume: -9.90 cc
• Compression Height (CD): 1.220 in. (31 mm)
• Wrist Pin Diameter: 0.866 in. (22 mm)
• Wrist Pin Length: 2.250 in.
• Wrist Pin Style: Floating
• Wrist Pin Material: 5115 Low Carbon Steel, Case Hardened
• Piston Inside Diameter: 0.566 in.
• Retainer Lock Style: Wire Lock
• Retainer Diameter: 0.866 in.
• Retainer Thickness: 0.063 in.
• Retainer Lock Part Number: 866-063-MW
• Top Compression Ring Thickness: 0.0400 in.
• Second Compression Ring Thickness: 0.0480 in.
• Oil Ring Thickness: 0.111 in.
• Wall Type: Chamfered
• Wall Thickness: 0.150 in.
• Piston Average Weight: 294 g
• Forging Type: Asymmetrical FSR (Forged Side Relief)
• Piston Material: 2618 Forged Aluminum Alloy
• Ring Set Part Number: JG1001-3425 (JE ProSeal)
• Cylinder Count (this SKU): 6 (Complete Set)
• Connecting Rod Length: 135 mm
• Stroke: 89.6 mm
• Manufacturing Origin: 100% USA

Included Components

• 6x JE Forged 2618 FSR Aluminum Pistons (87.00 mm Bore)
• 6x Wrist Pins (22 mm, 5115 Low Carbon Steel, Case Hardened)
• 6x Sets of Wire Lock Wrist Pin Retainers (866-063-MW)
• 1x JE ProSeal Premium Ring Set - 6-Cylinder (JG1001-3425)

Product Description

The JE Pistons 297173 is a complete six-cylinder forged piston kit engineered for the BMW S52B32US 3.2L Inline-6 engine found in the 1996-1999 E36 M3 and 1998-2000 Z3 M Roadster / M Coupe. Machined to an oversize bore of 87.00 mm (+0.60 mm over stock), this kit is the performance builder's choice for top-end rebuilds where cylinder bores require machining beyond stock dimension. Constructed from 2618 T6 forged aluminum using JE's proprietary Asymmetrical FSR forging technology, these pistons deliver the tensile strength and thermal stability required by the S52's high 11.5:1 compression ratio - whether the goal is a fully built naturally aspirated track car or a boost-fed street machine.

The inverted dome / dish crown design (-9.90 cc volume) is purpose-built to achieve an 11.5:1 compression ratio within the S52B32US combustion chamber geometry when paired with a standard 0.069 in. head gasket. The floating 22 mm wrist pin with wire-lock retainers provides smooth pin articulation under high-rpm cycling, while chamfered wall construction improves oil retention at the skirt for reliable cold-start protection. Valve reliefs are precisely radiused to match the S52's camshaft lift profiles, and all six pistons in the set are balanced within one gram to ensure smooth rotation throughout the S52's high-revving powerband. The included JE ProSeal premium ring set (JG1001-3425) is matched to the piston's ring groove dimensions for optimal sealing from day one.

This kit is designed exclusively for the North American S52B32US engine and is not compatible with the European S50B32 engine used in non-US M3 models, nor with any non-M E36 powerplant. Professional cylinder boring and honing to the correct piston-to-wall clearance specification is mandatory prior to installation. For single-cylinder replacement, order part number 297173S. Builders who require a stock-bore piston set should refer to JE's 86.50 mm (stock bore) option for the S52B32US application.