dual wastegate questions
 

so this is actually pertaining to my Supra but that forum is dead so I thought I might ask here...the same general principal applies and honestly the knowledge base here is really great.

I am running a precision 6466 on a dual wastegate ETS long tube manifold. My tuner said the base boost was too high at 19psi and we should target 14-16psi. I had put springs in according to the Tial MVR chart to make it 15.95 psi but that was wrong...I just removed the wastegates and removed one of the springs to make what the chart says is about 10-11psi but in reality is making 13psi. It was kind of a pain in the ass and hope I don't have to do it again, but I am wondering how you are supposed to properly calculate this or is it more of a trial and error kind of thing?

Also, I was reading that whatever wastegate spring you put in, you should run less than 2x the boost. So on a 16psi spring, run less than 32psi, etc. However, is this rule different on dual wastegates on a twin scroll turbo?

Same rule. If you are using both nipples on the wastegate/s with an ebc you get a bit more range.

so with my 11 psi springs, then I theoretically should run a max of 22psi? in this case, why does my car boost more than what the tial wastegate spring chart says it should?

Could be because the wastegate runners arent as efficient as possible, wastegate is slightly small, or Tial spring chart slightly off,, any number of things, doesnt sound bad though. At least you know where you stand in terms of what springs you want now.
A single port boost controller will net you no more than double whatever boost you get off the spring, a two port will net you much higher and will facilitate much softer springs if desired.

yea, each of the wastegates is using two ports (one lower and one upper).

All of these numbers are based around "general" engine condition/cam timing/flows/ignition timing/pump/ethanol fuel in addition to compressor/turbine match. If you stray too far from normal or manifold design is poor your results can vary.

I would suggest if the turbo is matched for top end power you may get closer to 2.5 times base pressure flat out if a bit smaller probably closer to 2 times as mentioned above. It's not just a linear maths things there are a heap of system interactions and its just a dumb spring.