There are no American made kits or engines yet, except for a v-twin 2 stroke, however that only comes on a complete bike and is VERY expensive. I don't remember what vendor it is, or even if they're still selling them. The design was based on the ht engine, but I dont think the vendors are members here. Anyway, the kits are all pretty much still the same, the 4 strokes being the obvious choice for long-term reliability. If you're looking for a little extra power, shift kit or a diy engine setup. I'm currently working on a 98cc 4 stroke build, and I'm not the only one by far. Not sure how long its been since you've been around, but there is a company called agk (www.affordablegokarts.com
) that is now designing custom transmissions for the Predator engines, but will also fit others such as my 98cc engine, and there is also of course the qmatic which can be adapted to many different engines. So there are other options besides the kits, not that there is anything wrong with the kits.