I wondered that also, but kind of figured it out. The Sti TMIC that comes with the JDM engine has different intercooler hoses that are free flowing stock, so they are not needed. The uppipe is already catless, so aftermarket uppipe is not needed. The pulley I guess you could do, but I would leave it off too. The only thing you have to worry about on the Jdm engines is putting larger turbos on them
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Plus injectors, larger TMIC, etc. Might want to do Turbo inlet also... Just take a look at the engine and you can pretty much tell what you need and what you dont.