Quote:
Originally Posted by Kingtal0n
If you have two identical examples with identical mass flows and turbine shaft speed, and you upgrade the downpipe or post turbine pressure drop efficiently, the only thing that will change is the wastegate fraction of ejected volume. The lower pressure means more exhaust can flow through (any type) of gate, whether internal or external or merged or divided etc... makes no difference, the flow rate will increase, which causes the gate to close slightly compared to previously, which means it is no longer "working" as much as previously. So if it was at 100% previously now it will be 99% or less, you gain gate effectiveness with no change to power, shaft speed, turbine behavior. Even though the post turbine pressure is lower the turbine never speeds up because we are manually controlling the shaft speed as a constant instead of a variable.
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I dont quite agree with this because you're assuming all wastegates are the same design. Yes, in theory this makes sense, but the whole point of a wastegate is to take some of the exhaust flow away from the turbine wheel and theres strong evidence that suggest different wastegates do this more effectively based on positioning. Take a look at the v1 Xcessive manifolds and their spiking issues. They remedied the problem with their v2 by angling the wg valve more toward the collector against the direction of exhaust flow. There are other variables at play here such as manifold runner design, valve size, EGT, etc. but angle this 90 degrees or even in the opposite direction and it just doesnt work as effectively, plain and simple.