This is a good point that I haven't thought about. And would be the easiest most direct route to exit the exhuast, I was pillaging around a area at work that stuff gets piled up and never used and I found a couple 5 inch rain caps that have been long forgotten that I saved just in case i decided to take it thru the top of the fenders and they would be easily removable for track outings.

Guys I can easily neck the pipe down to 4 inch if theres a need to. But in my opinion and correct me if im wrong a big block Chrysler proforms at its best with a good flowing exhaust ie big header tubes and the least restrictions as possible. Now a turbo car doesnt need the big primary tubes and the larger tubes and actually hurt your turbo spool characteristics. So IMO if I can fit the 5 inch pipe where it needs to go why not take advantage of the possible gains that running a free flowing setup might give me, and to my limited knowledge theres no downside to running to big of a downpipe.
Future plans are to run a aftermarket block with a 4.5 inch bore.....

Thanks and keep your opinions and ideas coming
Aaron

I know on my old Cummins going from 3"to 4" lowered egt's noticeably. I know there is a point where there is diminishing returns because heat can help spool up.

5" won't hurt anything. If you have space for it, go ahead and use it. If it gives you fits, go smaller.
The exhaust turbine works at its best when there is a wide inlet to outlet pressure ratio. I think you are distant from being at the point where 4 to 5 makes any difference.

Another example of More's Law:

If some is good,
More's better, and
Too much is just right

R.

For anyone that cares I got some info about sizeing of downpipes guy on YB says that 120% of the exh. wheel exducer is the rule of thumb for DP sizing

So If you have the 87/96 wheel on the S475's thats 3.4". So 3.5" off each turbo is fine.

If you have the smaller 74/83 wheel S475's then thats 2.9"... so 3" is fine.

That's assuming no sharp bends and a reasonable length of pipe. For most of the short dump style turbo exhausts 120% is plenty, no need for larger.

Keep up the good work

Thanks Fastmop mockup should be done in the next week, Im hoping to have it tore back down before the first snow fall. Plans are to clean the engine bay up,strengthen and lighten the K member,and finish the cage up,and get the car ready for some paint.
Ive also been tossing the idea of ditching the torsion bars and doing a coil over conversion while everything is a part but I haven't made my mind up yet, I had planned on running the car in some stock suspension classes and not sure how a coil over conversion will affect that decision.
Ill try and post a pic of final mock up in the next couple days.

Most "stock suspension" rules allow for coil over conversion as long as double A arms are kept, yeah? Chevy and Mustang guys can run bolt on front clips and aftermarket k-members and suspension...