Didn't dyno before and after. but my old extractor was a modified E36 RHD extractor (See pic)

Compared to this old extractor, the custom made extractor is way way better. The new extractor is mandrel bent stainless steel pipe with 4-2-1 design.
It's not the 4-1 design which would give you problems with road clearance.
Can't achieve equal length due to space constraint. This is almost as good as it gets.
Compared to the stock RHD, I would say it would flow better looking at Y-joints on the stock RHD extractor.

The custom extractor has a much narrower Y-joint angle which promotes better flow.
I've commented my other thread on the initial review.
I've taken the car for a long distance highway trip and can say the engine pulls a lot better from 140 to above 200. Can still go faster but i better not stress my well worn rear tyres. Will get the rear tyres replace before i try again to see where the car stop pulling on top end. (FYI, my M42 is running the E36 G220 with 3.15 final drive)
How much is it? I got made for about USD450. But subsequent units can be made cheaper...
I've taken some undercarriage photo showing the exhaust system. Will upload those later...