^Keep in mind you're talking about PEAK exhaust pressure. It's only that high around 7k.
That's why boost falls off so bad.
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Originally Posted by twiceblown
So, how are the guys like IPO, Jack T, and Monet actually boosting 30+PSI without huge amounts of exhaust energy being wasted through the wastegate port? Granted, i don't know what kind of actuators they're using, nor how much spring pressure they've increased by either preload or washers, but i can't imagine anything less than a huge amount of exhaust energy being wasted due to the "blow by".
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There is probably a large exhaust volume being bypassed at higher RPM, but there is also a larger exhaust SOURCE. Leaking 100cfm of exhaust might not be enough to drastically reduce boost at 6 or 7k, while it might at 4 or 5k.
I'm looking at this problem in part as a way to improve existing methods of boost control. External actuators don't NEED to be drastically inferior to externals, but they leave something to be desired in stock form.
Externals are superior in large part because they use very large diaphragms relative to the wastegate valve area (giving pneumatic leverage to overcome drastically higher spring preload), and because they apply boost pressure to CLOSE the valve until boost control is required. Externals are awesome, but the're expensive, bulky, and weren't designed into my setup (nothing against my headers and O2s, they rock).
-Chris