Is anyone using a 5zigen header and what if any differences did it make. From what I hear there are 3 diff types of headers they make, b20, b16 and type r. I was trying to find out which one I got. I ordered one from modacar.com for a gsr and I think I have a b16 the collecter looks to be under 2.5in and there is just a 5zigen emblem on the top of the header (4-2-1). But I had to run a test pipe, because it was too long for the stock cat. any help?