Thanx pretty much confirmed what I suspected.Here's my plan....

Since TTI don't make a 4" collectored header for the 426-1 heads I think Im gonna have to mod them and add the 4" collector.

Then dual 4" pipes from the collector to the X (or H) then muffs - 4" IN and 3.5" OUT. The reason for 3.5" out is by then the exh gases would have cooled sufficiently to allow a reduction in pipe diameter and to enable it to be easier to get over the diff.

After they go over the diff Ill run another 2 x 3.5" IN/OUT muffs at the rear to keep the noise to an acceptable level. The tank is in the trunk so I have the room to do it. The dual 3.5" pipes out to the bumper.

For you 4" collector guys, how is your ground clearance with them?

Thanx...