NJFZ1
Moderator
Just wanted to show a picture of the two side by side. All along I had thought that the stock header was a 4-->1, but it turn out that it's a 4-->2-->1 just like the Yosh. Biggest difference you'll note is how much longer the primary tubes (before they merge into the 2-->1) are on the Yosh. This is why this header provides such a nice torque boost in the midrange. I guess Yamaha had to merge their much sooner so that they could place the catalytic converter closer to the front of the bike (earlier in the exhaust path). This was done so that it could get up to temperature faster and therefore be more emissions "friendly".