I searched and cant figure out what is the difference between a stock wrx manifold and a twinscroll. I know it is for the vf36-37 turbo but why are these manifolds so expensive. (I assume they are some type of JDM part)

 

twin scroll turbos require twin scroll manifold and downpipe to fit on a wrx, in other words, you just can't buya twin scroll turbo and slap it on a wrx, you need the ts manifold and supporting parts.

 

yes but what does twin scroll mean?

 

Here are pics of the JDM STI twin scroll uppipe and header to give you a visual to compare with the standard USDM WRX/STI uppipe and header (not pictured)...I believe the downpipe has a different flange also.

 

"Based on experience gained in the WRC, Subaru is now using the latest twin-scroll turbo technology to allow for faster turbo response without sacrificing flow capacity. The unique twin-scroll equal length manifold now joins cyl. #1 with #2 and #3 with #4 to reduce exhaust pulse interference and ensure maximum exhaust energy is available to spin the turbo. Each cylinder pair is kept segregated all the way into the turbine housing" (from http://www.rallispec.com/sub_engineturbo.htm).

Does that help?