Porting and Pipes

[winslow]

Kind of new to the dirt bike scene- only had my KDX for about 2 months now, and have been reading the site and Canadian Dave's Tech Tips...

So, I was wondering what would happen if you had your topend ported for more bottom end and then added a rev pipe, and visa versa- mid/top porting with a torque pipe? Would it sort of "average" out, or would it not work that well?

 

[jaguar]

It wouldn't average out, it would cancel out.
Since you'd have to have lower exhaust ports for better low end, then you can't really port it for that. You'd have to lower the cylinder, say by just using gasket sealant instead of a base gasket. Also you can advance the ignition timing for better low end. I have advanced mine by 1mm at the timing marks and it made a significant difference.
I also did something you probably can't have done; I had a cylinder sleeve custom made that left .7mm overhang to lower both levels of exhaust ports. works fantastic. I get holeshots when I MX but it has good enough grunt to use 14/49 sprockets. I think the base gasket width is around .25mm