Porting 89-95

[motopsycho87]

So I buy Eric Gorr's "motocross&offroad performance handbook", looking at the preview on google docs it gives you porting advice on many bike and I saw in the index it has a section for the KDX. Getting really excited I open it, realise its written by Jeff Freddette and the only advise it "take it to me for a port job" whoopdedoo, money wasted.

So, has anyone broken the mould and experimented with their porting themselves? What did you do and what did you find? Thanks!

 

[Gone crazy]

I have ported just a couple of cylinders but have been riding for many years and had many conversations about porting, my first on i ported was an IT 200 yamaha that is a woods bike i raised the exaust port too much and ruined the roll on power you need for the woods but it would have worked on a moto track, I will give you the basics i know, dont raise the exaust port unless you want to give up bottom end for top end, in my oppinion for the woods be very carefull with the height of the exhaust port, you can be a little more relaxed with the intake side but dont go crazy makeing gigantic holes either you can flood the motor makeing it load up easy. In my oppinion just clean up and take out the excess flashing if you are the do it your selfer, Machines are required for any mayjor changes leave that up to the people who know what there doing. Cylinder head work is good bang for the buck it can even eliminate the need for porting, cutting the squish and milling a little off for more compression can really wake up some bikes beyond belief and its a 60.00 simple bolt on. There are many pipes to choose from also so the need for porting can be reduced. I guess my best advise is not to port aggressively or you will end up with a fishing weight, but im sure even the pro's went fishing a couple of times Hahaha

 

[Gone crazy]

Also they cut about 1mm off of the base of the cylinder of a motocrosser to give it more low end but they also have to cut up into the head to allow for for the 1mm they took off of the bottom this will raise the compression ratio.
high compression more low end. Lower compression more top end at the cost of low end.