Quote:
Originally Posted by wheela
This is close, but not quite. wgdc% controls the amount of vacuum sent to the wastegate canister - roughly, 0% wgdc = 0 vacuum sent, 100% wgdc% = 100% vacuum (around 26 in Hg) sent. But wastegate position is different. Without the car running, the wastegate should fully close around 6 in Hg. But with the engine running, exhaust gas pushes against the wastegate flap, which tries to push it open. So the same wgdc% will yield different physical wastegate positions, depending how much exhaust gas is coming out of the engine. Further complicating things, is that as exhaust gas flow through the turbine increases, eventually flow starts to choke, meaning it gets to the point where increasing exhaust pressure will not push any more flow through the turbine. In this case, you need the wastegate to flow the extra exhaust flow. There are maps in the DME that model these relationships. When you start modifying the engine, the maps no longer accurately reflect what's happening. Here's a screenshot from Garret showing the turbine choking I'm talking about. You can see as pressure across the turbine increases (the x axis), the flow through the turbine starts to choke out, so you stop getting more flow through the turbine, even as pressure is increased.
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Very interesting read. Never knew wastegates were this complicated.
Always thought WOT=closed - PSI target reached = open
I'll be posting updates on this problem I have.
Thanks!