Hello.
I am from Portugal and i own a 1999 classic shape Impreza.
As you noticed, I don’t post here much, but I use the search button a lot to read about your mods and your opinions about these.
My car has some mods, including a performance ecu. I was running 1.4 bar with the standard TMIC. A few days ago, I installed a huge FMIC and the pressure dropped about 40%. The reason, in my opinion, is due to the poor design of the tubes, wich are very large in diameter, causing a pressure drop.
I installed a manual bleed valve from Forge to raise the pressure again to 1.4 bar, because I cant modify the ecu parameters. I used the bleed valve together with an in-dash pressure gauge, and I was very happy with the results.
I don’t know why some people here say that bleed valves are not the way to go, if the original system by Subaru is nothing more than a bleed valve controlled by the ecu.
So why cant I have a manual bleed valve? Subaru chose this way to control the boost.
Some people even say that this is not a safe way to go, but they recommend some electronic gimnics like HKS or Blitz, that basically do the same thing and are not engine safe. The only difference is that they look good around the dash.

Another subject is the atmospheric bov. Some people here say that these bovs cause the engine to run rich when changing gears, because the MAF cant read the vented air.
How can the MAF read something that hasn’t passed through it? The original bov vents the air into the turbo inlet, to keep it spinning and avoid lag. If this vented air passes way far from the MAF, how can the MAF read it?

I used to own a 2003 Civic Type R, and I am used to all kinds of unproven myths in the forums.
Don’t get me wrong, this is just a different opinion about two things described above.
Just my 2 cents.

Regards.

 

i dont know a great deal about engines, but the sensor will have to read something would it not, even if that sensor picks up nothing, its a different reading than running with a recirc, there fore my guess is, is MAY cause the mixture to be rich, thus creating the damage

John

 

Not 100% on this but: the air you are talking about has technically been past the MAF as don't forget the pressurised air you refer to that is released either to atmosphere or back into the inlet (past the MAF) via the BOV was sucked in past the MAF at the outset. Think about it, there is only one way for air into the system and that is through the MAF, the turbo spools up by exhaust gases spinning the impeller wheel at the other end of the turbo sucking air in under vacuum through the inlet tract - at the end of which lies the induction filtration and MAF.

Also think about where subaru plumb back the air on a normal recirc valve setup into the inlet tract - in front of the turbo but behind the MAF as that air was already metered by the system on it's way in originally. They could have plumbed the BOV waste pipe back into the airbox in front of the MAF if it hadn't already seen it.

One more consideration, when running atmos BOVs it is a well known phenomenon to get more pops and bangs through the exhaust from that short period of overfuelling between gear changes when the car does run a bit rich due to metered air not being present. I.e the car already metered that air and the injectors are dutied to match with the correct amount of fuel. But because you've vented that air and the ECU has no way of seeing it - you run rich momentarily until you are back on the accelerator.