thanks all bro useful information. I just wanna know more about nitro car basic theory and for reference from some technique quiz like this post that I can't get any ans from web search.
as G4s, K-factory's "ED system" change the car "final ratio" to reduce engine loading and improve power transfer .and, my car just around 1st 18/52 ,2nd 24/47, I watch others car like NT1 spur gear up to 58..so, it blast me ask "gear ratio"