i was recently cleaning the boost soleniod on my impreza and i came across a small brass
'restrictor' in the pipe from the bottom of the soleniod to the air-box resonator thingy
i removed it and took the car for a run and found that i was now getting 1.0bar boost??
i put it back in where i found it
do they all have this or can somebody shed some light?
forgot to say before i was getting .8bar(wrx)



[This message has been edited by Dub Yar Ex (edited 08 December 2000).]

 

Be very, very careful - what was your peak... Not sure whether this also affects overboost protection?

IIRC the restrictor is in the line which bleeds pressure away from the wastegate actuator. Never been brave enough to play myself

Richard

 

Not checked myself but seen mentions of the restrictor on other Scooby sites. I think it slows down the rate at which the boost pressure in the lines escapes thru the solenoid, to 'smooth' the transition between on / off boost behaviour and make throttle response more linear. Dunno what long-term effects it would have by removing it tho'

 

The brass restrictor is a crappy and crude fix by subaru dealers/IM to overcome the overboost problems that later cars were encountering. Basically it reduces the boost available. The car overboosts if it is boosting more than around 1.2bar. My car used to try hitting 1.35bar when I had overboost problems. A restrictor was then added knocking boost to 0.8bar and stunting performance at the same time...which is why I pulled it out and fitted a boost controller instead!!

 

thanks for all the replies
erm well now......it peaked at slighlty over 1bar,somewhere between 1.0 and 1.1bar
is this safe ?
i hope to fit another boost gauge i have and
remove the restrictor(nervously this time)
and check exactly the peak or rather get my girlfriend to watch the gauge while i plant it!
does seem a bit of a crude way to restrict it though...



[This message has been edited by Dub Yar Ex (edited 08 December 2000).]

 

Anything below 1.2 bar should be safe, it would be wise to run on super unleaded 97ron as a precaution. I run mine at 1.15-1.18bar without a problem and have done for 40,000+miles.

Nito

 

You didn't mention what year car you have?
Normally removing this brass bit makes the car run lower boost. By decreasing the size of the hole you run higher boost.
On earlier models this was the other way around.
Careful guys when "playing with this restrictor as tiny hole size differences make a huge difference in Boost. ie: .7mm of a hole gives my car 1.0 bar of boost and .6mm gives it 1.4 bar of boost.

I have a full set of these restrictors.

Nito you are somewhat correct. Subaru used this rstrictor to control the overboost in MY98 cars in particular. not a great mad as it slowed down the car.

It wont affect your overboost protection but I'd still be very careful.

Paul.

 

Paul: as the car is now overboosting without the restrictor, it must have a 2 port solenoid. This was used commonly on the pre '98, and post '98 cars. The '98 has a 3 port, and is actually better at controlling boost.

There is NO hard and fast rule as to what boost a particular size retsrictor will give. A .75mm hole gave 22psi on my car (STi4) .6mm would have blown it up. Each car varies, just as some suffer from over boost, and some don't.

Nito: Restrictors are not just used by Subaru, they are used by just about every turbo car on the market !!!

The reason both you, and others suffer poor performance after "overboost" problems are taken to a dealer, is because the majority of dealers don't have a clue how to use restrictors correctly.

Of course an electronic boost controller will work better, but it should for circa £500 fitted !!!!!!!.

Nearly ALL of these problems occur after fitting free flow exhausts, and filters allowing the turbo to spin up more quickly. It's the ECU that can't cope, not the restrictors. The latest boost control software in the Possum Link, is TOO good, and now I struggle to get any over boost at all best I start playing with thoses cr*py restrictors again

Mark.

 

sorry.. its a 93 wrx so i guess it has a two port soleniod
so in theory if I had a pocketful of these wee brass restrictors I could go out and find an acceptable boost level within the standard ecus limits??
I don't think i'll be running without any restrictor now however now that I hear how
big a difference in boost a small difference in bore of restrictor makes!
not too keen on the idea of seeing daylight through my pistons...

 

Back in the dim and distant past my UK94 had one of these brass things in the pipe to the actuator. Fitting a de-cat SS exhausted did cause the turbo to scroll up faster and subsequently the ECU cut the fuel when it hit the overboost limit. (Brick wall effect)

Since then I've had an APEXI boost management thingy fitted which allows a greater control of boost.
(10 PSI low setting; 18 PSI high setting peak and hold)

Mark.

 

The car being an early one has a three port solenoid and the restrictor is there to slow down the rate of spool up and minimise overboost, it has a 2.0mm bore unlike the restrictors fitted to the later cars that have two port solenoids which is 1.0mm. This smaller restrictor also performs a different function in that it increases the rate of rise and held boost..

So removing it will allow the sleeve bearing turbo fitted to the car to spool up that bit quicker and it will, as has been seen, hold a touch more boost. Boost cut is at 1.15 bar on these cars. Sooner or later you may hit the "sweet spot" and then boost cut will operate. Fitting a free flow exhaust and air filter almost guarantees that you will hit the boost cut occasionally without it.

 

hey, thanks for all the information

Bob, I definently now what you mean about my turbo spooling up quicker...it was as if the boost gauge couldn't keep up with the gear changes which makes me wonder whether maybe it wasn't a very accurate gauge of the peak boost? I certainly wasn't hitting the boost cut(thats if i've still got one that is!?!,sure who knows what has been done to the poor creature in yapan??)

i'm actualy quite happy with the level of boost at 0.8bar
i've got a free flowing exhaust and filter fitted, and its spooling up quicker than it was before I fitted that...
i've took a mate that has a P1 for a run and he thought it wasn't any slower than his anyway.(but maybe he was just being polite of course?)

i'm certainly a lot happier now i've read all your replies.....i was a little 'concerned' when I first found it