Choose a vehicle:

User Tip: If you're unsure of your vehicle type, you may skip the machine type selection box.

» Log in to use your Rider Profile Machines

Please select make, model and year

Big Bore KitsBig Bore Kits

Big Bore Kits from Rocky Mountain ATV/MC

High quality off road big bore kits.

Latest Dirt Bike Big Bore Kits Reviews – You could win up to $500 for reviewing products!

  • Yamaha GYTR Ported Cylinder Head Assembly

    Yamaha GYTR Ported Cylinder Head Assembly

    James in TX

    GYTR Head

    Expensive engine mod but if you are serious about powering up your YZ grab this and get to the front. Need to use VP u4.4 but you should already be using that if your racing at all . Be sure to set the new mapping to the ECU !

    Read All Reviews
  • Dubach Racing Engine Relocation Kit

    Dubach Racing Engine Relocation Kit

    cody in MO

    Awesome

    Put this on my bike along with the Dr. D radiator lowering kit and the two together made my bike handling a lot better than it ever did before. Recommend both kits for anyone with a 10-13 yz450

    Read All Reviews
  • Cylinder Works Big Bore Cylinder Kit

    Cylinder Works Big Bore Cylinder Kit

    Joseph in TX

    Bolt on power

    Swapping out the old cylinder for the new was very strait forward and conversion fitted well with all mated factory parts. It was an easy bolt-on 8% extra power.

    Read All Reviews
  • Wiseco Big Bore 440 Kit

    Wiseco Big Bore 440 Kit

    TROY in CA

    Best mod ever

    This was buy far the best upgrade I did to this quad. Great fit.

    Read All Reviews
  • Athena Big Bore Kit

    Athena Big Bore Kit

    DAVID in CA

    Athena 290 big bore wr/yz

    I have ran this big bore for three years and have great success with it, makes great bottom end and mid range power. I have ran it on my 08 yz250f with a wr trans and rekluse clutch and hot cams, awesome woods bike.

    Read All Reviews
Frequent Buyer ProgramParts Finder