Ok, I found this from PMD.
http://www.ebay.com/itm/New-PMD-4-1-...-/111861062944
It doesnt really look bolt on, and I guess this design use more space, so I couldnt put it on stock 4x2 without moving the stock battery out. Also I see its 4:1.
I forgot to write my reduction is 6.43/1, so its slower.