klx 650 big bore kit hp in white letters on blue background with picture of klx 650 dirt bike

James Stewart

KLX 650 Big Bore Kit HP


Are you thinking about upgrading the engine of your (almost) 30-year-old Kawasaki KLX 650?

klx 650 dirt bike

You can do that easily by installing a big bore kit, and we will explain all the specifications you need in the following section.

KLX 650 Big Bore Kit HP (Horsepower)

The KLX 650 big bore kit comprises a cylinder body, cylinder head, piston, piston rings, and gaskets.

The piston bore dimension is 102.5 millimeters, an increase from the stock piston bore of about 2.5 millimeters. The increased piston size results in an increase of around 5-10 horsepower.

The stock piston and cylinder body size of the KLX 650 is measured at around 652cc, but with the big bore upgrade, this size increases to around 685cc.

According to the manufacturer, the stock engine parts give the KLX 650 hp of around 48.5 horsepower. With its larger size, the KLX 650 big bore kit hp will increase to up to 55 horsepower. (The popular Kawasaki KDX 220 isn’t far behind with 50 horsepower.)

Big Bore Kit Specifications

The KLX 650 big bore kit has the following specifications:

  • The piston skirt (the part that extends the lowest) is coated with molybdenum for increased resistance to heat and wear
  • The piston has dual pin oilers for more effective oil cooling
  • The pin of the piston is also coated with DLC (highly resistant Diamond-like Carbon material)
  • The compression ratio is increased from 9.5:1 from the stock to 9.7:1 with this kit
  • The parts are lighter but stronger than those that come with the stock engine
  • All the parts are manufactured with a forging method that increases their heat transfer capability, prolonging their lifespan
  • Due to the increased engine displacement size, vibrations are lowered to a minimum
  • The top piston ring is coated with ductile iron plasma to increase the tightness of the initial seal and prevent gas leak into the crankshaft
  • The two middle piston rings are coated with iron phosphate for better heat dissipation, while the oil piston ring is made from carbon steel to provide a complete seal

Performance of the Bike After the Upgrade

After installing the KLX 650 big bore kit, the bike will not change much visually, but its performance will noticeably improve.

The stock 652cc engine size delivers around 48hp at 6,500RPM. With KLX 650 big bore kit hp is increased to 55 at the same number of RPMs. 

The size is not the only thing that impacts this, but also its compression ratio, which goes from 9.5:1 to 9.7:1, increasing the overall torque and top speed of the bike.

The increased bore from 100 millimeters to 102.5 millimeters also increases the stroke size by around 4 millimeters, impacting the power output.

The improved materials of the big bore kit also allow you to push the bike harder, meaning you can ride it at higher RPMs and get more out of the engine’s power. They are more resistant to wear and tear and have better heat dissipation, especially the piston and rings.

If you’re having issues with getting the carburetor to run properly after adding the big bore kit, you can learn to diagnose a lean bog vs rich bog issue here.

Do you also want to know how Kawasaki got started and when? Learn about who invented the dirt bike here.

You can find other Kawasaki models we’ve reviewed: