Mostly the aftermarket. But the stock cylinder layout severly limits what can be done. And lastly money you can build a Honda for 1/3 the cost of a Suzuki just because of the aftermarket support. Everything we do is semi unique, We use as many off the shelf parts as we can. Ive even gone so far as to try other cylinders for the 250 but its so much work its not worth the aggrivation.