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#19: 10-18-2009, 09:16 PM
Title: Twinscroll troll
Rank: Donating Member
Location: Boston
Car: 05 LGT wagon 6MT
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Upgraded pump matters when you increase bearing clearances and plan to spin the motor faster. I run shimmed 10mm pump, and it holds pressure without problems. There are many schools of thought but I subscribe to the shimmed pump camp. 12mm pump (from some JDM engines) is considered unreliable. 11mm pump (08+ STI) has increased volume but not pressure. Extra volume is needed to drive exhaust side AVCS on 08+ STI. With extra bearing clearances/higher rpms there is no need for more volume, but more pressure, hence shimmed 10mm pump seems to make sense.