420/500/520 Primary (clutch) Reduction 80%

  • Sale
  • Regular price $950.00
  • Will not ship until



**Now offering "CUSTOMER CORE" options for a cheaper upfront cost to you. You MUST send us your stock clutch basket assembly upfront after placing your order. We will use your basket for your reduction and it'll ship back out the following business day after we receive your basket. If you choose the "CUSTOMER CORE" billet basket upgrade we still require your stock basket assembly before we ship your reduction. Email/message us for shipping info.

The website automatically displays the more expensive billet basket "RBM CORE" option, use the option box above to choose the cheaper cast basket or customer core options.

The "RBM CORE" price includes a $175 core charge on the aluminum clutch basket. Please send in your stock basket and include a copy of the original purchase receipt for the $175 core refund.

This is our billet 80% (actual 83%) gear reduction for foot-shift and standard ES machines. This reduction requires extra case clearance/cutting around the change clutch basket. Our stiffer stage 2 clutch springs are necessary with this size reduction. The stock clutch springs do not provide enough clamping force to hold the extra torque produced from the lower input ratio. Pic may not show correct size.


ES models will need an ES module to prevent electronic shift issues. Springs, ES modules and seal kits are located in the 420/500/520 sections and "Parts" section of the site.