A freind of mine is currently undertaking an S4 T2 engine/trans swap in his 85 GS.
Will the stock S4 T2 downpipe clear the FB firewall?
For the time being, he wants to use the stock downpipe (minus cats), and get a short pipe made to attach to the rear 1/2 of the RB single pipe FB exhaust. We both understand it is not optimal, but it will only be a temporary system. The engine is totally stock, with the only upgrade being a FMIC, rather than the top mount.
This is just a quicker/cheaper way to get the car running, considering all of the other stuff that has to be done. It will get upgraded to a full 3" exhaust, when his wallet quits smoking.

 

The stock "downpipe" which is just a precat,will clear no problem.
I still slap mine on during smog time,just in case the shop gets pickey about visual stuff.......I cant boost up past about 10psi, when its on there.

FWIW,with my first S4 setup,I was able to easily move 14psi through a good maincat and a crush bent 2.5" system I had made up cheap and hastily.The stock turbo was screaming,but it was quite fast.Dont expect it to be a slouch just because its not optimal!;-)

 

Thanks Steve. I thought it would work. I was pretty sure you (and a few others) could give me a definitive answer.
With everything else he has had to purchase, he just wants to make it run.
This option is currently available, as I only wanted the front 1/2 of the RB system....

 

I believe that's what Mike-P used on his.. The RB downpipe