Dirt Bike Cylinder head porting | Klx 110 pit bike build part 5

[@olivermuller7272]

To get a good result you should keep in mind that the diameter of the intake Port should not exceed 90% of the valve diameter. The majority of the gas volume will go the way along the long radius of the channel. In practice 70% go this way and only 30% go along the short radius of the channel. When you just make it bigger you remove material and you increase the port volume. This can have a negative effect because it slow down the speed of the airflow. From the diameter of the carburetor to the intake valve the channel should go smaller by 2% of slope. In the curve to the valve bowle widen the port a little around the valve shaft and make the stem more aerodynamic. The 5mm from the valve seat is quite important make it nice and smooth. The same in the combustion chamber, smooth all edges with 240 grid sand paper.For the intake port use 80 grid, exhaust port 120 grid or tape the valve seats for protection and use a sandblaster gun. The surface in the channels work best when the have a little roughness. Also measure the lift of your cam. As a rule of thumb a good lift is calculated by intake valve diameter divided by 4.

[@chrisfayling]

Great information! Thanks man, there is not a lot of information on this. It’s all secrets. I’ve learned of the years just work of mouth and playing around with different heads. Eric Gorr has some books out that I have that talk about specific bikes and different ways to port them, but it’s good to know th general rules of thumb. I always take my intake to 80 grit, and I knew to of course make sure just past the seat to be smooth, but you taught me somethings. 👊🏼✊🏼

[@Greybuiltracing]

Where do u get all this info from ? Can u help me with some references ? I’m about a lil over a year building 4 stroke engines and dragging mini bikes . I know about smoothing out the corners on the intake but would like to know where else on these heads can I improve on . Pics and vid’s would be great .

[@Greybuiltracing]

Also is rougher then 80 grit ok?

[@chrisfayling]

@@Greybuiltracing most the knowledge I have is from the old techs at the dealership. Look up Eric Gorr, he has some books out. Unfortunately there isn’t a lot of information out there on this stuff, lots of secrets.

[@chrisfayling]

@@Greybuiltracing tougher than 80 grit would be fine, look at how rough it is from the factory