If so what kind of gains could we expect to see say
at 400, 500, 600+ compared to plumbing it back in the dp?

 

All depends on the setup. stock frame internally gated turbos will probably see 20-30 whp. I could be wrong but this is based off what i've seen in the dyno thread.

 

My personal experience was a loss of 35whp @ 425whp routing the exhaust back in to my 3" DP. I took care to route it in along way from the turbine wheel and it merged into the outside radius of a bend so that it was a straight shot down the downpipe. In other words, about as good as it could possibly get. At the time, my trap speeds dropped from 121-122mph to 117-118mph. I pulled it back out and ran it open again and trap speeds went right back up.

 

It's not a direct apples to apples comparison, but I added a MAP o2 dump and some head porting to my setup and gained 40 whp on pump gas with a BBK-Full.