30 replies to this topic

[Subaru_Bloke]

Hi guys, I found this guide on another forum about restrictor pills and found it very useful. It could even become a sticky.
 
Apologies if it's a repost, common knowledge or I'm not allowed to link other forums.
 
The restrictor pill in a Subaru WRX is simply used to change the volume of air traveling down a vacuum line, in the case of most WRXs bar a few of the latest ones and ones running stand alone electronic / manual boost control EBC/MBC systems this restrictor pill is vital. 

***edit: any 'new' style ebc will negate the need for a restrictor pill (but can still be used and may well smooth out boost further and also reduce initial waste gate pressure). The older 3 port boost controllers will not. Please see Jimbo's drawing in the post below***

It's located in the vacuum line between the turbo compressor housing and the T piece that connects to the wastegate solenoid valve and the wastegate actuator. (see below image )
 

This image has been resized. Click this bar to view the full image. The original image is sized 960x640.

If your vacuum line that should have the required pill is missing the restrictor you will have boost fluctuations and often only hit the wastegate preset pressure of your turbo "often this is a lot lower than the desired boost level"

If the restrictor pill is inserted but twisted or blocked you can have major issues extreme over boosting for example, this could *will* cause all sorts of problems.



Every variation of the WRX requires a specific sized pill:




Model.............................Orifice....P/N#..............MSRP...Notes
2006-2007 WRX-0.8mm...0.0315 ..22326AA260... $4.00~ Line Asembly Pink dot
2007 STI .......................0.0335 ..14447AA140 ..............Line Assembly
1.0mm ..........................0.0394 ..22326AA010... $2.00~
2004-2006 STI ...............0.0430 ..14447AA090... $20.00~ Line Assembly Yellow Dot. 2008 STI 14.5 psi max
2004-2005 FXT-1.2mm ...0.0472 ..22326KA120 ...$2.00~
2002-2005 WRX .............0.0472 ..22326KA120 ...$2.00~ 2008 STI 14.3 psi max.
2005-2006 LGT ..............0.0490 ..14447AA120 ...$16.00~ Line Assembly
2008 STI .......................0.0350~ 14447AA250~ .$85.00~ Line Asembly? Aqua Dot. Determined size from measuring. 

2007 STi WGDC Tables
Stock restrictor pill size = ~.0335”
Factory wastegate pre-tensioned to ~9psi
2004-2006 STi WGDC Tables
Stock restrictor pill size = ~.043”
Factory wastegate pre-tensioned to ~10psi
2005-2006 LGT WGDC Tables
Stock restrictor pill size = ~.049”
Factory wastegate pre-tensioned to ~10psi
2004-2005 FXT WGDC Tables
Stock restrictor pill size = ~.047”
Factory wastegate pre-tensioned to ~7psi
2004-2005 WRX WGDC Tables
Stock restrictor pill size = ~.047”
Factory wastegate pre-tensioned to ~6psi
2002-2003 WRX WGDC Tables
Stock restrictor pill size = ~.047”
Factory wastegate pre-tensioned to ~10psi

MY93-96 ... 3 port solenoid 2.0mm restrictor fitted into the vent pipe between solenoid lower port and intake
MY97 (Euro) ... 2 port solenoid 1.2mm restrictor fitted between the turbo and the tee piece
MY97 (JDM) ... 2 port solenoid 0.9mm restrictor fitted between the turbo and the tee piece
MY98 (Euro) ... 2 port solenoid 1.2mm restrictor fitted between the turbo and the tee piece
MY98 WRX (JDM) ... 2 port solenoid 0.9mm restrictor fitted between the turbo and the tee piece
MY98 Sti 4 ... 3 port solenoid 1.5mm restrictor fitted between the turbo and the solenoid adjacent to the solenoid top port
MY99 (Euro) ... 2 port solenoid 1.2mm restrictor fitted between the turbo and the tee piece
MY99 (JDM) ... 2 port solenoid 0.9mm restrictor fitted between the turbo and the tee piece
MY00 (Euro) ... 2 port solenoid 1.2mm restrictor fitted between the turbo and the tee piece
MY00 (JDM) ... 2 port solenoid 0.9mm restrictor fitted between the turbo and the tee piece
MY01-05 (Euro) ... 2 port solenoid 1.2mm restrictor fitted between the turbo and the tee piece
MY01-05 STi ... 2 port solenoid 0.9mm restrictor fitted between the turbo and the tee piece
MY06/MY07 both WRX and Sti 2 port solenoid 0.9mm restrictor between turbo and tee piece
 
Taken from: http://www.perth-wrx...y-you-need.html

[Dylan]

Useful information mate !

[Subaru_Bloke]

It's too bad there is no information for Liberty/Outback/Foz, but armed with this information, a clever fella might look up his repair manual and find out the correct sized restrictor for their applicable vehicle - and it's hopefully stated!

[Jimbo]

If using an aftermarket EBC system, you wouldn't need the pills at all. The newer BCS work a bit differently to the ones used in old systems. The old ones used to be a 3 port design where there was in, out and bleed off which went back to the intake. Newer ones just have a line ( as you can see above ) teed off the wastegate and compressor line which goes to the BCS. The second hose from the BCS then bleeds to the intake. 

The restrictor pills should only be necessary using the stock BCS setup. All they do is limit the flow to the wastegate and BCS so the wastegate doesn't blow open early. It's all in correspondence with the pressures the stock BCS works with, gives smoother boost control and a more linear power delivery. However, hooking up an aftermarket EBC or MBC would negate the use of the pills as they can manage the desired pressure, usually utilizing a 3 port design, much like the early BCS setup ie in-bleed-out.

I love mspaint so much i have explained how each BCS system works.

[Subaru_Bloke]

Brilliant work Jimbo. I was actually wondering why it states in the post that ebc don't fix the restrictor problem, as I thought they monitored manifold pressure and compensated on the fly.
I will edit post with the info you have provided.

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[Adam]

Strange. I have an EBC with what I think is a 3 port, but only 2 ports are plumbed up.

It works, but I've often wondered why there's a 3rd port

[Dav_fre]

3rd port is bleed

Plumb it back to intake for some extra measured air

[Adam]

So back into the manifold?

[Subaru_Bloke]

Yes. Before the Turbo, after the air filter. Although I doubt it would make that much difference? Someone with more knowledge should answer though

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[Adam]

I'm curious as to why it would be left off.

Just went and checked out the setup.

One line goes to the little nipple on the compressor, one line to the wastegate and then the EBC is plumbed to the manifold. Leaving the NC port open.








I should not, my car seems to have run fine like this for like 180000kms, so this is more just a discussion because I've always wondered why!

[Jimbo]

Quite possible some EBC's just bleed air off to atmosphere.

[Dav_fre]

I always thought bleeding anything to atmo was a big no no

??

[aekOne]

Adam 3 port is normally plumbed like this: 

 

[Subaru_Bloke]

Aek, that pic states you still need a restrictor pill for 2 port boost solenoid??

Which one is it? Far as I can tell the restrictor pill decreases the wait for boost by stopping the wastegate from opening as far, thus reducing the time to close for boost. Anyone want to jump in?

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[Jimbo]

Way to steal my mspaint thunder, Aek!

The reason for a pill in the 2 port design is probably much like the reason for having a pill in the BOV line. It basically just smooths out the system. Also, note the shape of the hoses, without the pill the air would just go straight for the wastegate.The pill slows down the pressure buildup and let's the BCS do it's thing efficiently.

[Jimbo]

That COBB tuning description is brilliant, i'm going to copy paste. Aek make sticky?

[Adam]

Really digging this discussion Something I can actually follow!

[aekOne]

the factory set up is a 2 port system with the restrictor pill located on the compressor side of the t-piece feeding to the bcs. it's only when going to a 3 port bcs that you do away with the restrictor pill

[Jimbo]

http://www.cobbtunin...les-s/70674.htm

[Subaru_Bloke]

I got a restrictor pill made up the other day and put it in today. It has solved my boost issue. I am using a greddy profec ebc which has 3 ports, but the manual only says to hook 2 up.

It has made my car much more responsive and boost higher and harder.

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