Tell me about the bypass valve
#1
Rainman
Rennlist Member
Rennlist Member
Thread Starter
Tell me about the bypass valve
My basic understanding of the 951 bypass valve is that when you close the throttle, the air basically bounces back down the pipe the direction it came, and the valve sees this pressure being higher than it should be, opens the valve and routes that pressurized air to in front of the turbo, after the AFM, to prevent that air from slowing down the compressor wheel. It is a blow-off valve that "blows" back into the intake.
Is this correct? If so, what kind of pressure is needed to make a stock valve open? And does this valve work when off-throttle, routing air around the turbo?
Is this correct? If so, what kind of pressure is needed to make a stock valve open? And does this valve work when off-throttle, routing air around the turbo?
#2
For the most part yes, I don't know if you can really describe it as the air bouncing back down the pipe in the direction it came. It's more like the air hits the closed throttle plate and backs up on itself, eventually making its way to the compressor wheel and causing compressor surge (a fluttering sound, I'm sure you've heard it before). The bypass valve does just what you said, by re-routing the air in front of the compressor housing but after the AFM so as not to turn into a rich situation. The valve itself is controlled via vacuum.
#3
Addict
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Rennlist Member
It is open during non boost driving, yes.
#5
Three Wheelin'
No, its just being drawn through via vacuum, it still has the same path.
This website has a diagram to help you understand a bit better
http://en.wikipedia.org/wiki/Blow_off_valve
This website has a diagram to help you understand a bit better
http://en.wikipedia.org/wiki/Blow_off_valve
#6
Three Wheelin'
The valve will open when if intake vacuum is sufficient to overcome the spring pressure, but the bypass side of the valve is not connected to the plenum. Either way, this should not happen if the valve is functioning properly.
The actuator side of the valve, which is connected to the plenum, is just a dead end as far as the plenum is concerened.
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#9
Three Wheelin'
Yeah, it can be done. The air fuel ratio will go super rich for a second, because you'll be venting metered air. If you went to a speed-density system, this would not be an issue.
#11
Blow off valves have a spring in there.. some higher, some lower, but like to remain closed.. When you shut the throttle butterfly, it creates vacuum.. that vacuum pulls against the spring ,opening the bypass valve.. it will not want to open until there is enough vacuum to overcome the spring pressure. (usually light) When you boost.. the boost pressure pushes at least the same boost lbs your runinnng against the valve plus the spring pressure... therefore shouldnt' open no matter how much boost you run....... because the same boost pressure is being used to push it closed.. always equal.