90" Monster Big Bore Kits / Sportster

Revolution Performance 90" Monster big bore kit for '91-'20 Harley Sportster motors.

The Sportster responds hard to displacement, and this Monster kit takes the 883 or 1200 platform out to 90 cubic inches. Revolution Performance builds the cylinders in NSC plated aerospace aluminum with no sleeving, so the big bore is possible while friction and temperatures stay low. It ships with flat top 10.5:1 pistons and a gasket set. Black with highlighted fins. Requires case boring.

Features

• Aerospace grade all-aluminum cylinders with a nickel silicon carbide (NSC) electroplated bore
• No sleeving, which allows for larger bore sizes
• NSC plating reduces friction for more horsepower, lower engine temperatures, and longer lifespan
• Includes a pair of NSC coated cylinders, custom forged pistons with high tension rings designed for NSC bores, and a head and base gasket set
• Replacement gasket sets available separately
• Upgraded cylinder studs and head bolts recommended
• Made in the U.S.A.

Specifications

• 90": 3-7/8" bore, 3-13/16" stroke, 10.5:1, flat top pistons, 62cc heads
• Fits '91-'20 XL Sportsters; XR1200 requires gasket kit part 09343181
• Requires case boring

Note: No shipping to California.

Frequently Asked Questions

Do I need to bore my cases?
Monster big bore kits require case boring. Bolt-on kits do not. Check the specific kit and ⚠️ VERIFY your case and head combination before ordering.

What head do I need?
Each displacement is matched to a specific head chamber volume. Match the kit to your heads exactly, since compression depends on it.

Are pistons included?
Yes. Each kit includes custom forged pistons with high tension rings designed for the NSC bore, plus a head and base gasket set.