ORIGINAL: Ricardo M.
Thank you very much for your answers.
What about the header? I´m using a Macs header ( the taller one 2.25") with the standard aluminium OS pipe. Does the header makes any difference in the final result?
Not really. I THINK the OS header is a fraction longer, but in the end it makes no difference. I like the OS header because the o-rings allow the engine to move and not put undue stress on the header. If you mount the pipe at the coupler right behind the header, and somewhere else further down, this allows the whole assembly to give a little. I have seen quite a few Macs headers break because of vibration, never seen an OS break under any circumstances. If it moves TOO much you may have to replace the o-rings occasionally, but that's all.
-Mike