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Old 11-15-2012, 03:54 PM   #1119
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Member#: 103631
Join Date: Dec 2005
Location: Mililani, Hawaii
2004 STI


Originally Posted by kellygnsd
I don't know what egbp #'s you've seen but the ideal ratio is 1:1 boost to egbp so for 20 psi boost you would want about 20 psi egbp. The ratio is higher during spool up too. Subarus never acheive this 1:1 ratio and in reality more in the realm of 1.5 to 2.0.

Think about this then, a turbo running 20 psi with a 1.5:1 boost/egbp ratio would have 30 psi egbp steady state, but much higher egbp during spool up.

While its not crazy pressure I could easily see 30-50 psi forcing open the wastegate against a weak spring.
Is the back pressure due to the head design or the extensive preturbo piping? I've always wondered.
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