Trilogy of Power: Pipe/Head/CDI

Pipe: an expansion chamber is the main determinant of engine powerband (RPM spread of power) and peak power. Aftermarket ones are available or you can use my pipe calculator to design your own. Check it out at How an expansion chamber works

Head: the head determines engine compression and squish clearance (which determines squish velocity). If the clearance is too much then power is lost due to excess fuel/air mixture “hiding out” in the squish area when the piston is at or near TDC. Stock clearances are almost always too much, designed that way to compensate for manufacturing tolerances so that none of the stock engines will have too little clearance. All stock engine owners should measure the clearance and then use a squish velocity calculator to see how much the clearance can safely be lessened. Lessening the clearance a little bit makes a big difference in the squish velocity but little difference in the compression. Here is my squish velocity calculator: Squish Band Velocity Calculator

CDI: the CDI provides a set timing advance that changes with RPM. Graphing RPM and timing results in the timing curve. The stock KDX CDI is designed for moderate power since it is basically a trail bike. For maximum power it needs to gradually retard more (ie: closer to TDC) as RPM increases from 6000. For a more complete demonstration of this please watch my video at
Porting: Most bikes come with adequate porting for the intended use of the bike so it wasn’t included in the “trilogy”. But if you want a trail bike to be more like a motocrosser then raise and widen the exhaust port and the transfers (or put a spacer or extra gaskets at the base of the cylinder and then have the head lathed down to reduce the squish clearance to what it should be). If you want a motocrosser to be more like a trail bike then lathe some off of the base of the cylinder and either add a head gasket or have the squish band machined for correct piston clearance since the head will then be closer to the piston.