CRACKERS i stand corrected ,I was looking for 5 equal length exhaust runners.
Yes, it is the 5 cyl manifold. Due to space restrictions on these motors/chassis’ it is very hard to build an equal length manifold (and is quite unnecessary) as it becomes a huge heavy device that also transfers a ton of heat into the power steering rack and brake booster. Equal length is only of any real functionality if built (designed) within a specific tuning parameter in correlation with intake manifold, camshaft timing, compression, RPM criteria etc.
For 400hp a reasonably flowing manifold (such as a lightly ported Japan manifold) is all that is needed....i’ve Cross-sectionally cut apart the original TTRS manifold and although the design is quite nice, the runners are tiny and the collector atrocious...yet guys are making 700+hp and running 9 second 1/4mile times through the original Audi manifold. I would suggest the Audi and Volvo manifolds probably flow about the same at a given pressure ratio.
Now, if you go build a large manifold to run with a smallish turbo you will also lose some spool apart from the heat issues mentioned. For 600hp absolutely...a tubular manifold, done right, will come into it’s own.