Suddenly confused about recirv valve
16 September 2005, 04:35 AM
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Suddenly confused about recirv valve
Please bear with me, altho i know there are many threads on this topic, heres my observation.
I was arsing about in the Forester today, and thought it would be cute to disconnect and block up the pipe that leads from the standard RCV back to the inlet pipe so that the valve vents to atmosphere and see if I noticed any change in behaviour, and make some noise over the weekend.
While I had the engine running, I noticed that the valve does open when the car is idling, since the manifold vacuum pulls the plunger up, when revving lightly it stays partly open, and the more rev, it closes down as the more the pressure in the intercooler and manifold balance out, and the valve remains closed until of course throttle closes and it blows off the pressure.
I was shocked, because I thought that the valves remain entirely closed until they blow off boost coming off throttle.
In this state, it seems to me there is no way you can run a standard valve as a VTA, because there is entirely too much MAF measured intake air being blown out at idle and low throttle, plus of course when blowing off boost.
As a side note, I did this both with the stock plastic valve (my98), and a metal one off of a WRX that I had an adaptor made to fit, thinking it was a better unit to have in there than the plastic one, oddly enough, the plastic one had a stiffer spring and smaller plunger opening at idle.
What I wanted to confirm was that this is all normal, and that real VTA valves remain closed at idle and low throttle, and only open when actually dumping boost?
And I also want to know why this is done, is it simply a result of having both sides of the plunger affected by pressure with a moderate pressure spring.
Or is it intended that the valve open and recirc air from the intercooler back to the intake so that the compressor wheel can spin more freely (e.g at idle the compressor will spin more freely than if it were only blowing against the closed throttle plate and idle control).
Maybe its a non issue at that low rec level of air flow, but i just had to ask these things.
I was arsing about in the Forester today, and thought it would be cute to disconnect and block up the pipe that leads from the standard RCV back to the inlet pipe so that the valve vents to atmosphere and see if I noticed any change in behaviour, and make some noise over the weekend.
While I had the engine running, I noticed that the valve does open when the car is idling, since the manifold vacuum pulls the plunger up, when revving lightly it stays partly open, and the more rev, it closes down as the more the pressure in the intercooler and manifold balance out, and the valve remains closed until of course throttle closes and it blows off the pressure.
I was shocked, because I thought that the valves remain entirely closed until they blow off boost coming off throttle.
In this state, it seems to me there is no way you can run a standard valve as a VTA, because there is entirely too much MAF measured intake air being blown out at idle and low throttle, plus of course when blowing off boost.
As a side note, I did this both with the stock plastic valve (my98), and a metal one off of a WRX that I had an adaptor made to fit, thinking it was a better unit to have in there than the plastic one, oddly enough, the plastic one had a stiffer spring and smaller plunger opening at idle.
What I wanted to confirm was that this is all normal, and that real VTA valves remain closed at idle and low throttle, and only open when actually dumping boost?
And I also want to know why this is done, is it simply a result of having both sides of the plunger affected by pressure with a moderate pressure spring.
Or is it intended that the valve open and recirc air from the intercooler back to the intake so that the compressor wheel can spin more freely (e.g at idle the compressor will spin more freely than if it were only blowing against the closed throttle plate and idle control).
Maybe its a non issue at that low rec level of air flow, but i just had to ask these things.
Last edited by Joth; 16 September 2005 at 04:54 AM.
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