Ive heard of people modifying their jdm header for a little more power. How exactly do I do it? Do I just cut out the smaller circle part inside the collector?

thx

 

also how far do i cut in?

 

look inside where the welds are and there is a BIG NASTY ridge from the welds coming inside on the head side , get some grinding stones and make it as smooth as possible
dont go crazy or you will need to get the outside rewelded , but i smoothed mine out almost perfect and its still fine
I have to say that for no money spent i did notice a little power, its a BIG rough edge