I know this is a often asked question but I really just want a decent answer if possible ..got a friend who has a friend who does a lot of port work he told me he would give me a extra head an port an polish it for me for 150 I hear he’s really good an a very trustworthy guy what kinda Gains should be seen over my stock 400ex head 5hp? An does this actually do the atv any good like longitivity wise or does it more less add performance an hurt the engine