The header on my 08 wr450 is smaller in diameter that my sons 08 yz450. I know that this is meant to enhance the low/mid power to match the intended purpose of the bike. So, has anyone swapped to the larger yz or gytr or an fmf power bomb (along with a different muffler..I have the fmf Q4)? What did you notice in power quality/quantity from the header change? By the way, I ride mainly so. cal. desert so mid/upper is used mostly.