[brianlo622]

There is a slight difference between JDM OEM and JDM aftermarket.. with that said, some people might even argue if an in-house tuner is considered "OEM" for a manufacturer.

A few examples of in-house tuners for Japanese car manufacturers:

Mugen for Honda
Mazadaspeed for Mazda
Ralliart for Mitsubishi
STI for Subaru

etc etc..

Toyota is an interesting exception, since TRD has a Japanese Division (TRD Technocraft) and an USA division (TRD USA).

I am more of a fan of following a factory, in house tuning program, rather than being a "JDM whore". However, when it comes to TRD, I will always try to pick up TRD Japan parts (TRD Technocraft) over TRD USA parts. The reason is because TRD USA does very little to spend time and money to R&D their own parts.. majority of the time, they work with an American manufacturer and rebrand their products as their own.

Just my $0.02