I've seen some discussion on different types of bleed valves. Can I assume that this is the restrictor on the line between the turbo compressor and the wastegate actuator?

If so, does anyone know the size of the orifice in the restrictor in a standard 220hp WRX and a MY01 STI? Trying to get this info. I'm guessing that its around 0.75mm.

Many tks.

 

Between the turbo outlet and the T-piece. 1.2mm in UK MY01 WRX. STi tends to have a smaller restrictor. Altering the restrictor or adding a bleed valve doesn't tend to increase held boost (unless it cannot reach target) as the ECU controls the duty cycle to target held boost within limits.

There are the usual factors to consider if you are doing this in terms of monitoring engine safety. If you don't know what these are I suggest you leave well alone.

 

Truth be told, I'm trying to slightly reduce boost from stock levels on my MY01 STI RA in the interests of longevity. My std restrictor has an orifice of about 0.75mm. Have increased it to 0.9mm and the boost seems to have fallen a tad.

I'd agree with you that the held boost in the steady state should not be altered by messing with this restrictor IF the ECU is reading boost and pulsing the solenoid based on that. But I was under the impression that the solenoid is pulsed in the open loop. A larger orifice will allow more air thru, and assuming that the boost solenoid pulsing is similar to the original unmodified state, the wastegate should be opened sooner?

Anyone know for certain what the ECU takes into consideration for control of this solenoid pulsing? If it reads boost, won't that be considered "closed loop control" already?

tks.

 

John, this was from an eariler post from you back in Nov:

"I am beginning to belive that the solenoid map is only based on throttle position and RPM with no element of closed loop boost control on the ECU - otherwise the held boost would not change with valves, but it very obviously does."

Do you still think this is true?

 

No I don't believe that anymore. The reason I thought this I think now is because on the old shape the control system has quite limited bandwidth, and offsets do occur, but it is closed loop. I gather on the MY01 it is even more strongly closed loop from what people say. On the old shape I understand there is a TPS/RPM lookup with a duty cycle for spool up and then another table for held boost.

However, if I were you I would leave your boost standard as Subaru designed it, especially on the new shape. If it is running to spec I can't see the engine longevity being poor?

On the old shape you clearly could reduce held boost by increasing the size of the hole in the restrictor.

 

Tks John.

But if the boost is indeed closed loop controlled from the factory, why does the boost reach 1.4bar with WOT in gears 4 and 5, while it only reaches 1bar in gear 1 and 1.2bar in gear 2?

It was this phenomenon that led me to think its open loop control.

 

I agree - it is closed loop but only for held boost and of very narrow control bandwidth so it does not always do a good job.