Originally designed by Eric Gorr and commissioned by Magnum distributing under the brand name MAGNUM MX COMPONENTS. I've converted thousands of YZ250s to big bores since I first invented this kit in 2008. These top end components are the latest generation of design and investment cast for the highest quality. These parts will interchange with all of the top ends processed by my company and Millennium Technologies as well as aftermarket kits like the CYLINDER WORKS which is another kit that I designed. $850 USPS Priority Mail included Components like the cylinder heads and powervalves are available separately and fit the OE Yami cylinder, CYLINDER WORKS ans ATHENA. The cylinder heads are available in different compression ratios and the option of EZ starting with a decompressor button. Please check those product pages for options and prices.We offer 3 choices of porting powerbands to suit your riding needs and 2 fuel choices. The porting powerbands are: Low to mid for single trail trail riding Mid top top end revs 1,000 higher than stock Wider powerband for a mix of riding from mx to off-road. The fuel choices are up to you and the choices are pump gas 10% Ethanol 89 RON and race gas of 98 RON or greater. We also offer high altitude head mods for no extra charge.Eric Gorr ports every cylinder by hand then signs and dates his work.These kits include a ported and Nikasil plated cylinder, cylinder head, all 3 powervalves and center retaining clip, new Yamaha studs, and COMETIC MLS head gasket and top end gaskets, o-rings, and copper washers. The forged and coated piston kit includes 2 rings, pin, bearing, and circlips. $825 with USPS These kits fit the model years of 1999-2025 YZ250
