Hi there, I'm searching for the optimum exhaust for good over all power. Engine is 4.2 ltr., 9:1, XJ6 S3 Head with Multi Angle Valve job and some porting, S3 cams, Weber 45 DCOE, Mallory distributor. So - original cast-iron, short primary pipes or long like the patriot header? 2 "secondary pipes? I ...