90.5mm x 82mm Hypereutectic Piston Set, Set of 4

OVERVIEW

When it comes to building a high-performance air-cooled engine, the 90.5mm bore is widely recognized by master builders as the "sweet spot" for balancing displacement gains with structural integrity. This AA Pistons 90.5mm x 82mm Hypereutectic Piston Set is specifically engineered for enthusiasts who demand more than just a stock replacement. By utilizing a hypereutectic aluminum alloywhich features a high silicon contentthese pistons offer superior thermal characteristics compared to standard cast alternatives. This material choice results in a piston that expands less under the intense heat of a high-performance combustion chamber, allowing for tighter cylinder-to-wall clearances. The result is better oil control, reduced piston slap during cold starts, and a significantly longer lifespan for your engine''s top end, making it an ideal choice for a daily-driven street sleeper or a rugged off-road dune buggy.

These are not your average pistons; they are designed specifically for "stroker" applications. While a standard piston is designed for a 69mm stroke, these units feature a relocated wrist pin height (compression height) to accommodate an 82mm crankshaft without the need for excessive shimming or overly long connecting rods. This geometry is critical for maintaining a proper deck height and ensuring your compression ratio remains within a tunable range. Included in this set are four precision-matched pistons, high-strength wrist pins, and wire-style circlips. Whether you are aiming for a 2110cc powerhouse or a torque-heavy 1914cc build, these AA pistons provide the architectural foundation needed to handle the increased mechanical stresses of a long-stroke Volkswagen engine while maintaining the cooling efficiency that air-cooled cylinders require.

FITMENT

This piston set is designed for Type 1, 2, and 3 air-cooled engines that have been machined to accept 90.5mm cylinders. Compatibility includes:

• Volkswagen Beetle: 1954-1977 (Requires machining for 90.5mm cylinders and stroker crank clearance).
• Volkswagen Karmann Ghia: 1956-1974 (Requires machining and stroker-specific case clearancing).
• Volkswagen Bus / Transporter: 1955-1971 (Type 2 engines only; requires performance machining).
• Volkswagen Type 3 (Fastback, Squareback, Notchback): 1961-1973 (Requires machining).
• Custom Dune Buggies and Sand Rails: Any Type 1 based engine utilizing a 78mm to 82mm stroker crankshaft.
• Note: These are "B" style pistons intended for use with stroker crankshafts (typically 78mm, 80mm, or 82mm).

SPECS

• Piston Diameter: 90.5mm
• Stroke Compatibility: Optimized for 82mm (Stroker / "B" Style)
• Material: High-Silicon Hypereutectic Aluminum Alloy
• Wrist Pin Diameter: 22mm (Heavy Duty)
• Compression Height: Reduced for stroker applications (approx. 24mm)
• Ring Grooves: 1.5mm Top, 2.0mm Middle, 4.0mm Oil Ring
• Set Includes: 4 Pistons, 4 Wrist Pins, 8 Circlips
• Weight: Weight-matched in sets of 4 for engine balance
• Piston Top: Flat top design for versatile compression tuning

PRO TIPS

1. Precision Deck Height Measurement

When installing 90.5mm pistons on an 82mm stroke, your deck height is the most critical measurement for both performance and engine safety. Because you are using a "B" style piston designed for a longer throw, you must mock up the assembly without rings first. Use a depth micrometer to measure the distance from the top of the piston to the top of the cylinder at Top Dead Center (TDC). We recommend a minimum deck height of .040'' to .060'' for street engines. If your deck is too tight, use copper head gaskets or cylinder base shims to achieve the correct clearance, as this prevents the piston from contacting the cylinder head at high RPMs when the connecting rods undergo thermal expansion and "stretch."

2. Mastering Hypereutectic Clearances

One of the greatest advantages of hypereutectic pistons is their low thermal expansion rate, but this means you must be very specific with your cylinder honing. Because the piston doesn''t grow as much as a forged unit, you can run tighter clearancestypically between .0015'' and .0025'' depending on your specific application and cooling capacity. Always check your ring end gap before final assembly. For a performance street build, a general rule is .004'' of gap for every inch of bore. For a 90.5mm (3.563'') bore, a top ring gap of approximately .014'' to .016'' is standard. Failing to gap the rings correctly can lead to the ring ends touching as they heat up, which can snap the piston lands and destroy your new engine.

3. Proper Wrist Pin Lubrication and Clip Seating

During the final assembly of your AA Piston set, pay close attention to the wrist pin installation. Use a high-quality assembly lube on the wrist pin and the small-end bushing of the connecting rod to ensure there is no "dry start" galling. When installing the wire-style circlips, ensure the gap of the clip is facing either 12 o''clock or 6 o''clock (relative to the piston crown). This prevents centrifugal force at high RPMs from compressing the clip and allowing it to pop out of the groove. Always double-check that the clip is fully seated in the machined groove by trying to rotate it with a small pick; if it spins freely but stays in the channel, it''s locked in and ready for high-revving action.