It appears the MR20DE throttle body is of near identical design to the HR16DE and 10mm larger. They can be found for roughly 85$ used online. The Japanese forums and performance shops all use larger throttle bodies in their tunes. I believe they use a mix of a bored out stock one and the MR20DE.
Since I'm still trying to fine tune my intake and have confirmed through testing and logging that the ecu has accurately compensated for the increased flow (not running lean), I'm considering adding in the larger throttle body and increasing the intake size to be more uniform behind the air filter (4" in/out). Right now I'm down stepping from 4" to 2.5" OD. I'm just not sure how worth it it would be with the stock diameter MAF housing in there.
Anyone else look into or attempt a throttle body upgrade?