NefMoto

Reading the various threads on here, it seems the general consensus is external boost controllers don't play well with ME7. Using an external controller with an external gate, you feed charge pressure to the bottom port, and modulate the top port through the solenoid to keep pressure in the top port to aid in spoolup. Some of the senior members suggest using only the bottom port with the N75, and leaving the top port vent to atmosphere. My questions are when using an external gate..

1. Are we leaving spool-up on the table using this bottom port only N75 method?
2. Is anyone have the N75 configured using charge pressure to the bottom, and N75 to control the top?

Using the N75 to control the top of the wastegate was something I was planning on trying at some point. Never quite got around to it. I believe, in theory, all you need to do is directly invert the output of the N75. I think a cheat way to do this would be to invert KFLDRL, so for all values where ldtvr_w = 0 input, output 100%, and visa versa. I usually linearize KFLDRL when I'm retuning for different turbos and recalibrate the PID maps to the new turbo. Having the three-port boost control on the wastegate is nice to aid with spooling and also for holding pressure at higher RPMs. When you only use the bottom port, the exhaust pressure from the engine tends to force the springs open too early, so you end up needing to use a larger wastegate spring than with 3port control.

As a side note, external boost controllers (while I despise them on principle) work fine with ME7 if you tune the control system correctly. You can pretty much make this control system do whatever you want if you know what to change.

Here is an image of the way I imagine you plan on connecting the N75 for 3port control. Please correct me if I'm wrong:
(https://static.cobbtuning.com/cobbtuningweb/site/images/accessport/SubaruBoostSystem_24.jpg)

Diagram is correct. I agree (at least in theory) with you on flipping the map(s). I also agree with being able to use EBC's with ME7 to a decent degree being mapped for the purpose. My goal is to focus on tuning external gates over the next week in depth. Going to log charge pressure only, the current EBC, and finally ME7.

I would agree in using the bottom port only and then using the N75 as it would normally to control the boost via KFLDRL. No need to invert as you are using a duty cycle as it would normally be used.

Its very much like tuning a stronger spring actuator.

The diagram you posted would work with the reversed N75 but sounds a lot of hassle and providing you have a strong enough spring in the thing it should spool fine and anway.

I agree. In theory, your approach should work.

The down side to having a crazy high spring is the lack of decent part throttle control.

Wastegate has a 15 lb spring now (Probably run 25ish on pump), but it's a 1.8T, has an intake cam, and a pretty big journal bearing turbo. Just looking to optimize the setup as much as possible, and look into different ways to control the gate. I didn't choose the hardware.  :) Thanks for your input. Hopefully if work stays manageable, I should be able to get some data on the differences this week.

I don't see how all of this is going to help the spool up? What can a softer spring in a wastegate do that will help the turbo spool faster?
I say 15psi for running 25psi should be fine hooked up the old fashion way. From my reading in the past using 2 ports helps control
boost creep and spike but don't see how it could help spool up.

Using a light spring (within reason) makes it possible to run less boost, and control boost better at part throttle. Putting pressure on the top port helps keep the wastegate shut, where only using the bottom port, it starts to open gradual as it meets spring pressure. This is based on my logs. The solenoid keeps pressure in the top port and starts to regulate (bleed off pressure) when it's very close to the target, rather than the gate cracking open earlier that it will become static at. You can also control the spike, and creep like you mentioned. Added benefits.

I have done it both ways, for me it just comes down to how much boost vs spring pressure.

Often you do not need the top port. On a high boost setup you may for holding it shut and spool up.

I use this method on my shop car for max boost and aggressive spool. Ignore the fact its not an N75, the NO (normally open) NC (normally closed) and C (common) still operate the same. WGDC is applied as normal.
(http://legacygt.com/forums/attachment.php?attachmentid=80638&d=1266762721)