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Edit3 9/7/13: Hi/Low boost switch works like a charm

So... looking at the parts for my (inoperative) EBC setup, and having played with my MBC again recently as well as the stock boost control... an idea struck me.

What if, for the price of a solenoid and a switch, I can plumb in both the MBC and the stock boost control in such a fashion as to provide two levels of selectable boost and give me the main feature I want from an EBC?

My idea is thus:

Split the turbo outlet control line to both the BCS and MBC inputs; add the stock restrictor pill on the BCS line as normal.
Run the output from the BCS to the aftermarket solenoid's input, then that outputs to a tee. The other side of this tee gets the output from the MBC, and then the tee joins them together for the final output to the wastegate port.

Run the aftermarket solenoid's power to a +12v ignition-switched source along with a switch in the cab. This switch should now select between your stock 8.7psi and whatever you have your MBC set to! Mind you, this is all theoretical at the moment, but I can't think of any reasons right now why it wouldn't work. I want to try it, is what I want to do...

And hey -- a potential enhancement, since this IS a solenoid hopefully capable of handling pulse width input power for controlling flow.... change the in-cab switch to an in-cab knob that controls a simple PWM (pulse width modulation) output from an IC or microcontroller, and that knob should roughly translate into a simple EBC -- allowing you to set the maximum boost with the MBC and "turning it up" from stock boost level all the way up to the MBC level, with the knob, at will

Just thought I'd toss this out there before I get a chance to try it, and see if anyone raises any serious concerns here. I'm quite excited to get something to test here!

Edit: The only thing i can think of so far is perhaps it would be a good idea to put in check valves on both MBC and BCS outputs to prevent reverse flow paths.

Edit2: Nevermind, all good. Latest updated system drawing / sketch shared, updating first post with it:

Could you draw a diagram in paint or something that shows what you're wanting to do? I think I know what you're trying to do, but I've read over your wording/description twice of how you have things configured and I still don't have a clear picture of how all the lines would be hooked up.

Just so you know, there is no (at least from what I have seen) restrictor pill in the turbo Legacy boost control setup. The restrictor pills are typically used in the bleed boost control setups found on the newer WRX's & STi's.

The main issue I could see with this setup would be complexity and it maybe not reacting as quickly or how you intend for it to react. I suppose though, you could always try it and see.

Oops! Not restrictor pill, I meant the reducing connector (the union between line L and line M on VRG3's vaccuum diagram.

Anyway, sure! This idea just struck me this weekend randomly, and I wanted to document it well so I could refer to it later. I indeed do plan to just try this out and see how it works. At the very least, I believe that the dual boost levels with switching should work just fine, I am unsure however if a knob would be able to realistically provide intermediate boost levels between the min and max set by the BCS and MBC.

Here's a quick diagram I tossed together in Visio 2013 since that's what I had handy:




...Thoughts?

(EDIT: switched from TinyPic over to Photobucket as they support auto generation of IMG tags with thumbnails for neatness)
EDIT2: Intended setup / operation example:

* Stock boost control regulates at 8.7psi using boost control solenoid (BCS)
* Manual boost controller (MBC) set to regulate at 15psi
* Air solenoid wired to a simple on/off switch in the cab, which provides wither 0V (off) or +12V (on) to the solenoid.

Switch to OFF position, 0V sent to solenoid, air allowed to flow through BCS == car boosts @ 8.7psi
Switch to ON position, 12V sent to solenoid, air not allowed to flow through BCS == car boosts @ 15psi
(EDIT3: The above on/off logic may be reversed, but whatever -- the switch would allow choosing between stock boost levels and whatever your MBC is set at)

....See any reasons why this wouldn't work...?

I think it should work, but those small 1-way check valves tend to leak a little bit, so I'm not sure if that would cause a problem. All you can do is give it a shot.

I really think setting up a PWM solenoid to vary boost is going to be a little difficult, but the on/off type setup certainly has a better chance of working properly.

would it even need the 1-way check valves? With the solenoid closed, no air should be getting out that way, and with it open, as long as it isn't over the opening pressure of your MBC, that should stay shut too. But even so, the MBC would see the same pressure on both sides, so it shouldn't open anyway, no matter the pressure.

Ah! Yes sir thank you for that logic, makes sense to me! I think ill give this a shot here soon. ..if this solenoid I have here still functions, that is.

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Got the test car back in the garage for some poor man's EBC goodness. The solenoid that came with my nonfunctional EBC is indeed functional! I just need to find an appropriate thread hose nipple for the outlet (currently vented to atmosphere, which is suboptimal anyway) and I can wire / plumb this up in time for WCSS 15

Plumbing & wiring now... testing hopefully tomorrow (later today?)

Plumbing and underhood work / wiring to cab complete. Finish wiring and switch mounting tomorrow. Woohoo!

Updated drawing to be scanned and shared as well.



(I know, that's clearly washer / vacuum tubing front and center there for the main BCS input line, but I'll replumb this all with matching tees and oil-rated tubing once it's been tested and played with sufficiently)

Updated drawing / sketch of the whole system plan:

Initial ghetto-rig install completed! Plan to mount the switch right next to the 5MT shift pattern label once I get a chance. At least now I can test it out on the way to the Sherwood Pick n Pull! Cmon, working Subaru alternators for $43 each....

This works great! Tested on way to junkyard, before rain. Git rained out after pulling only 1 alternator. $43 with 13mo warranty, neat!

Anyway, on the way home in the heavy rain couldn't get into boost without fuel cut. Behaved like issue with pressure sensor. Boost lines all still on. Currently suspect water causing issue with one of my splices below the hood scoop where water flowd freely in... I need a new hood.

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look forward to seeing it at wcss15 tomorrow!

Indeed, I've gotten it all dried out and confirmed the voltage issues seem to have gone away again... found the suspected culprit splice that I'm rerunning the wire for.

Pulled fuse 14 labeled (EGI/TCU) from the fuse panel at the driver's kick panel for 30-45 minutes, to reset my ECU to unlearn all the pressure sensor issues it just experienced on the drive home from the junkyard. Installing alternator from JY, hopefully it works - and I've got my ticket purchase confirmation printed as well as my directions to the event. Can't wait!

If there is a turbo hood for sale there I may consider it... I'd like a stock scoop with rain protection and diverter in place. My scoop just gathers water at this point - Oregon is different than Nevada in that regard, lol

If it weren't for the usefulness of the turbo chimney / heat shield, I'd go with an N/A hood since I'm FMIC anyway...

Got it; aside from a badly-placed splice directly under the hood scoop (which has been reran a different route), I also discovered that the soldered ground connection for my FCD had decided it was going to break; rigged that back up and I believe I'm back in business! To WCSS15! ....in the morning. (yawn)