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Old 06-26-2018, 11:38 PM   #3
Back Road Runner
Scooby Guru
Member#: 60082
Join Date: Apr 2004
Chapter/Region: MWSOC
Location: Minnesota
2004 Forester STI


I have a 67 with the 7cm^2 and it's small for HP. It definitely chokes peak output. However, I am also not capable of surging the compressor. You won't surge the 63 either. Basically, 7cm^2 or 8cm^2 is a choice of where you'd like the powerband. 7cm^2 vs 8cm^2 has a pretty small difference in dynamics or the point of spool up, so you're picking small differences. I haven't used both on a Steamspeed, but I have on an 18G. It basically meant 300rpm difference in spool up. Once up in the operating range you'll likely be hard pressed to notice a difference in dynamics. Peak output, I'm not sure. I need to dig up some old dyno info or data logs with MAF info.
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