If your yz85 just isn't mean enough, make it meaner. 53mm bore. Forged piston and stroker crank. This is a really nice package.
From Athena themselves,
"Athena's Big Bore kit brings the raw power you have been missing in an easy to install, reliable package that bolts on with no machining needed in most cases, and includes easy-to-follow step-by-step installation instructions. Constructed from aluminum, the cylinder is lined with a nickel-carbide coating for durable, reliable performance, and the water jackets have been widened for a higher flow rate, cooling the cylinder, resulting in less power lost due to heat. Features a forged piston that's been molybdenum coated for high performance use and extended wear life. Includes: big bore cylinder, big bore piston, piston pin, piston pin rings, gasket kit. Note: To achieve optimum performance re-jet the carburetor with the available jet kits. Fits: Yamaha YZ 85 2002-2018."