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Old 11-19-2012, 02:54 PM   #670
Ziggyrama
Scooby Specialist
 
Member#: 53665
Join Date: Jan 2004
Chapter/Region: NESIC
Location: Northboro, MA
Vehicle:
2011 STI Stg2 w/EBCS
2012 Tribeca Ltd.

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@jebjkey, it makes sense. Advancing intake valve at high load opens the valve too early such that the piston is still moving up and slowing the charge down. Also, you have to consider when intake valve closes. If you advance too much, you will move the closure too close to piston's BDC which at high load is not beneficial. In that scenario, you want to close it sometime after BDC because the air rushing in has momentum and can compress against the piston and be trapped in the chamber as it starts to move up. Another point to consider here is that when you advance intake, you create overlap with exhaust valve which in FI applications is not desirable.

Single AVCS STIs are simpler in the way you can tune this and your options are more limited. Dual AVCS really helps in certain scenarios. But that is a story for another time

Lastly, I really hate when people talk about spool and boost as measures of performance. These things are so subjective and typically their interpretation is wrong. For example, more boost earlier in RPM range is typically considered to be a good thing, except that most of the time, more pressure in the intake is a representation of lower VE which "looks" better but it most likely is costing you power. Bad, bad, bad.
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