[Splinter]

A motor is a motor is a motor. eg33 or ej22 they obey the same basic rules. 600hp is the same amount of exhaust flow whether its coming from a 1.8l inline 4 or a 7 liter V8.

What was your highest dyno number? Just did a quick search and all I could find is an old post from 07 with only 230whp.

Besides, you're supercharged, not turbocharged, which makes a HUGE difference in this discussion. A supercharged motor is a lot like an N/A motor in the exhaust department, you want the exhaust out of the engine as quickly as possible, with scavenging being the only thing to be concerned about. With a turbo setup, between the motor and the turbo you want to do anything you can to keep the exhaust gases hot, under pressure and with the pulses as close together as you can. This makes for a faster spool. Multiple dynos have shown time and time again that headers on a turbo subaru hurt performance until you start getting into the 500whp range. They kill spool times and take away a lot of bottom end in exchange for small gains at the top.

If I were to turbo an EG33, I'd use the stock manifolds, then build a collector/uppipe with a similar design to the turbo 4s, if possible (havent looked at the bolt pattern), flip them around, run a crosspipe across the front of the motor, and put the turbo in front of the passenger footwell. At any rate, even if you did decide you needed to build custom headers, there isn't more than 200 bucks of material in there.

I might not have as much experience with the eg33 specifically, but I'd hazard a guess that I've built as many subie motors as anyone else here. I'm not building an eg33 because my svx is supposed to be my comfortable DD. My impreza is my fast car.