I was browsing pocketbikesunlimited and saw their "Hitman Big Block" and it said how it increased top speed and throttle response. I would like faster speed and response on my stock x18, but I thought I heard somewhere that there is a cheaper one on ebay but didn't know what to search to find it. What is the product on ebay called that does the same thing but is much cheaper? Would the "Hitman Big Block" increase my bikes top speed and throttle response if it is all stock except for a new air filter? And would it hurt the engine? Thanks guys!