AXYS 860 Big Bore Kit for 2015-17 800 H.O.


Regular price $2,795.00

  • Kit is available for all 2015-17 AXYS 800 H.O. models

  • Huge gains in horsepower and torque when used with our supporting mods

  • +34-35 horsepower!

  • Kit requires: BMP Fatt Azz Pipe, BMP y-pipe, Bully Dog GT with BMP tune,Stage 2 clutch kit

  • Big bore muffler is required when riding 0-6000 ft altitude

  • 2015-17 models require a 2018-Up Thermostat and stat housing (additional $50)

  • Need replacement wrist pin bearings? Find them here

  • **Must send in cylinders and complete exhaust valve assembly (Do NOT disassemble), and your top case half** Package all contents VERY CAREFULLY and insure the package. BMP is not responsible for damages that occur in shipping. Core parts must be in good, usable condition. Parts not in usable condition will not be credited and the customer will be responsible for return shipping.

  • Turnaround time can vary from 1-4 weeks for this kit depending on if cores are in stock. Please e-mail or call for availability. 

  • Use this Work Order Form when sending parts so shipping/receiving knows how to identify them.

  • Part #: ADBM09-306

Cylinder Core Exchange Options (see drop-down menu):

  • Option 1: Purchase Outright - No core cylinder or exhaust valve assembly is required to be sent in (top case half still required to be sent in) - Raises kit price by $1500

  • Option 3: Exchange Parts - Your order will be pulled on our shelf waiting for your exchange cylinder & exhaust valve assembly to arrive. Once they arrive, we will normally ship the kit within a few business days. No core charge will be applied since we will have your cylinder and exhaust valve assembly prior to shipping the big bore kit.


  • Must have Muffler with low elevation


Are you looking for the most possible horsepower and torque from your AXYS 800 H.O.? You should know by now to look no further as we crank out the most powerful Polaris 800 motors on the planet. Our big bore kit delivers with unreal performance and great longevity. We spent many hours on the dyno developing this kit and a full year on the snow testing to perfection. This kit cranks out 190 horsepower with huge arm pulling torque! Our recipe is simple yet effective. We start off with boring your stock cylinder out for those larger pistons. Next we draw out a cylinder port map and get to work machining the ports to the specs we know provide the most horsepower possible. The cylinders are then sent out for Nikasil plating and measured to make sure piston to cylinder clearances are within spec. Once the cylinders are 100% completed, we must bore your top case half and grind your exhaust valves to match the bore and port (Must send complete exhaust valve assembly, DO NOT DISASSEMBLE THE ASSEMBLY). The next step is our billet head kit with our specially designed domes for the 860cc power plant which are available in low compression or high compression variations. Our custom made Wossner pistons are about as trick as a piston can get! These are coated to help aid break-in and lubricate the skirts. These are also our Durability piston style in which the skirts are longer for less piston rock and increase top end life. The Durability pistons also feature lubrication holes and rings that have increased spacing for better cooling and stability.

This kit must be used with our BMP pipe, BMP Y-Pipe & our custom tune loaded via the Bully Dog GT. Clutching is also 100% necessary and we of course recommend our Stage 2 clutch kit which has been tested with our big bore kit at all altitudes. If you are riding below 6000 ft you will also need to purchase one of our big bore mufflers for proper performance. Choose between our stealthy Full Velocity or the light and loud Powder Lite. See the complete big bore kit kit which comes with everything needed to take a stock sled to a complete monster!

Cylinders and exhaust valve assembly are on an exchange program while we require the customer's top case halves for machining. Depending on exchange cores stock, turnaround time is 1-4 weeks on this kit. Please e-mail or call for current availability.

BMP big bore tuning through the Bully Dog GT explained: Our custom tunes for the Bully Dog GT are state of the art and actually reprogram your ECU. No piggyback controller manipulating injector pulse width signals.... we go right to the source and modify maps the correct way. On a normal big bore you add quite a bit of fuel. With a standard piggyback controller that fuel is added no matter what map you are running in, and builds on top of correction factors. This can be troublesome when riding in warmer temps, and at different altitudes. Since our programming adjusts the stock map, the correction factors properly adjust the entire map... making for a smoother running machine that has great power at all temps and altitudes. We also are able to add more oil, fix warm weather maps, fix steady state lean maps, control the exhaust valves, and adjust fuel + timing accordingly. Oh.. and if that's not enough this is an extremely handy gauge which shows EGT's, engine knock and so much more... and data logs all of it! For even more information on this device please see the Bully Dog GT specific product listing.

No single action on your part is as important as proper engine break-in


Do not operate at full throttle or high speeds for extended periods during the first three hours of use.

Watch the video below for proper engine break-in protocol: