John ( & others w/67 & newer Imperials) Find a set of "C-body" factory HP manifolds and go from there. If you have the 70 something Imperial with the last designed exhaust manifolds just have the diameter the size of the manifold into the "X". You will always get lookers to stay longer over the stock appearing set up using the above than over the tube header with the above. As for myself, I am limited by frame design to the 1959 to 1966 factory cast iron exhaust manifold, which I run into the "X" and etc. Look at it this way, the 413 with single exh was rated at 340 hp, the dual exh was a notch higher. The 440 with single was 350 and the standard dual was 365 and the HP version with 375. Add the "X" and you just added power again over your prior rating no matter which engine you have ( 318, 331, 354, 392, 413, or 440 ) in your Imperial. And since it flows better your emmissions test out better. Rodger & Gabby Colo Spgs '47 De Soto Custom w/Fluid Drive & passenger door mounted swamp cooler '63 Le Baron w/F-Sweep trunk lid & std A/C '66 Le Baron w/dual A/C & reverbed AM/FM '70 Overlander - InterNational Dbl '77 D150 w/360, NP 4 Spd, 12 Bolt Axle, OEM Buckets & etc ----------------- http://www.imperialclub.com ----------------- This message was sent to you by the Imperial Mailing List. Please reply to mailing-list@xxxxxxxxxxxxxxxx and your response will be shared with everyone. Private messages (and attachments) for the Administrators should be sent to webmaster@xxxxxxxxxxxxxxxx To UN-SUBSCRIBE, go to http://imperialclub.com/unsubscribe.htm