I’ve seen multiple FDs pick up 1-2lbs of boost by switching from a RB dual to other 3” catbacks with Zero other changes. I used to remove RB Duals all the time from FDs I bought to sell and put on lower cost cat backs.

Wasn't that what you were running when you tuned your car at addicted? The stock port 8374 with water meth on a haltech? I had my very similar setup tuned there a couple weeks ago, but we ran into some boost control issues.

I was running the original Greddy SP which is about the same but just quieter.

Tanabe Touring Medallion seems to be the new GreddySP. But, man the SP was sweet. Just the right kind of noise.

No, but many FD exhausts do.
You can google image search for 1993 RX7 exhaust to see.

N1 style exhausts (loud) place the muffler at an angle to eliminate the bend just before the muffler.

Some large oval muffler systems (quiet) have a bend at the rear subframe, a straight section and then the bend just before the muffler. Flows much better than an "s" bend.

Some exhausts increase pipe diameter from 3" to 3.5" near the first bend at the subframe to reduce restriction further through the two bends.

Some others do have a tight "s" bend just before the muffler.

Racing beat has one extra bend the opposite of the "s" bend at the rear subframe to make room for the "s" bend interrupted by flanges. Flange mismatch is another point of possible restriction unique to the RB exhaust.

https://cimg9.ibsrv.net/gimg/www.rx7...37852e4df1.png

what manifold and wastegate were u running?

Me or David? I assume both of us had the .92 IWG 8374. I think he had a manifold built by Addicted. Mine is Turblown's short runner cast manifold.