i have the 88cc full GYTR big bore kit, its funny you dont find them anymore there all 84cc kits, but dirt rider did all theer testing on the 88cc GYTR kits , but i like mine, i mean it was basically $1000 after it was all said and done, and it nearly doubled in power! but i am sure the TBR kit would be sick!
The TBR kit is nice...expensive for what you get, but nice. It would be great for dirt. I have the kit on my TTR50 and I had to go to a 15 tooth front/32 rear sprocket setup to get it geared right (roadracing use). First gear is now somewhat useable for the tight stuff..and it pulls really strong through the top of 3rd. I am running the Sheng Wei 20mm carb btw.