Yes, u have to get custom ewg set up, but EWG is not as crucial on 18G, imo.

Response will depend on how good is ur tuner. Kinugawa has larger thrust bearing design. I never c a brand make ball bearing turbo for 08+wrx.

U have to be really careful about ur gearbox, anything more than 400nm torque (which will be certainly achievable with 300whp) can be dangerous though.

Both HKS EVC 6 and Blitz sbc electronic boost controller have twin solinoid and can support up to 5 boost settings, so u can use lower setting for dd and max boost on the track, but again depends on ur tuner's ability.

Im a fan of japanese tuning style (response) rather than american style (power).

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MY08 STI 422whp at 1.5bar on E85, built by Diversion Garage, assembled and tuned by EvoR

Update from new owner: 375whp at 1.4bar on 98, at Tokyo Motorsport