143" | 139" Monster Big Bore Kits / M8 Motors

Revolution Performance Monster Big Bore Kits take a '17-'22 M8 to 139 or 143 cubic inches on aerospace grade aluminum cylinders with a plated bore.

No Shipping to California.

The M8 responds to displacement, and these kits go after it with cylinder technology rather than brute machining. Aerospace grade all aluminum castings carry a nickel silicon carbide bore plated directly onto the aluminum, which removes the iron liner entirely. Less friction, better heat transfer out of the cylinder wall, and a bore that can go larger than a sleeved casting allows.

How the Monster Big Bore Kits Build Power

Plating the bore instead of sleeving it does two things at once: horsepower goes up because friction goes down, and engine temperature drops because aluminum moves heat faster than iron. Cooler running is what protects the investment over the long run. Each kit ships with a pair of NSC coated cylinders and custom forged pistons carrying high tension rings designed specifically for plated bores, since rings meant for iron do not seat correctly against NSC.

Monster Big Bore Kit Specifications

• Fits '17-'22 M8 motors
• 143" kits fit 114" and 117" motors: 4 1/2" bore, 4 1/2" stroke, 11.4:1 compression with 88cc heads
• 139" kits fit 107" motors: 4 1/2" bore, 4 3/8" stroke, 11.2:1 compression with 88cc heads
• Aerospace grade all aluminum cylinders with nickel silicon carbide electroplated bore
• Custom forged pistons with high tension rings matched to NSC cylinders
• Finishes: black, or black with highlighted fins
• Made in the USA

Installing the Monster Big Bore Kit

These kits require case boring, so shop time is part of the budget. Revolution recommends upgrading cylinder studs and head bolts to handle the increased pressure. Replacement gasket sets are sold separately for later service.

⚠️ VERIFY your current motor displacement before ordering, since the 139" and 143" kits start from different base motors. A displacement change of this size requires retuning.