I'm currently building a turbo setup for my car, not a miata but since there is so much turbo knowledge here I'd figure I'd ask here. The car is a toyota glanza 1.3 turbo. I just made a header and downpipe for it, so I could mount a Holset HE200WG Turbo (Awesome little turbo, here is the compressor map of it
Now, during the assembly I found that the wastegate was too strong for my application, The stock CT9 wastegate had a cracking pressure of about 10 psi, and was fully open at 20 (This does not directly reflect turbo pressure because exhaust backpressure also helps pushing the wastegate flap open). The holset had a wastegate cracking pressure of about 20 psi, and was fully open at 40psi. Now to remedy this I added a spring to the wastegate flapper to reduce the boost pressure:
The problem with this is that this makes the cracking pressure teeny, like 3-5 psi or so, but to fully open it still about 30 psi or so is needed. I ran the car like this to see what it does, and it seems like this hurts spoolup. It's very easy to get into positive boost to about 0,3 - 0,5 bars or so, but there is more lag before it's up to it's maximum boost level of about 1,2 bars than what I'd like.
This brings me to my question, what is preferred for the behaviour of the wastegate? I noticed that with stock diaphram wastegates the cracking pressure is about half of the fully open pressure. But since I have plenty of room near the wastegate actuator what would happen if I machined up a larger piston type actuator which uses a longer spring. I think I can make it so the cracking pressure and fully open pressure to be closer together, which should be good for spoolup, but might cause the pressure to fluctuate more easily. Anyone messed around with this? I ideally would want the turbo pressure only to be regulated with a wastegate actuator while having good spoolup. The car runs on a megasquirt, and I have a MAC boost control valve installed, but I can't seem to get it to work right. The valve acts very non-linear.