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[Jim Simms]

As I wait for the new motor to be dropped in, other new stuff will need to be added.

I did not see a "blowoff" valve listed in the repair manual, only the by pass valve.
Please jump in to clarify my misunderstanding, and explain the advantage of a blow off valve over the bypass valve.
Seems both kinda reduce pressure and keeps from extra fuel to be dumped through injectors.
Does the bypass valve vent the pressure (between shifts) from the intake pipe to the exhaust side of the engine?
Cant find that diagram.
What bad things can happen if the bypass valve malfunctions? Would the fuel mixture run rich and you get a puff of smoke after shifting?

I am guessing it would not run rich all the time since there is little pressure when idling.

If the blow off valve vents to the atmosphere (whooooosh), does it connect on the exhaust side of the engine like the bypass, just allowing "some"  pressure to be released ?

Seems I might have seen a blowoff valve hooked to the intake tube with no hose going anywhere.

What type of blowoff valve do you guys recommend?

If the blowoff is preferred to the bypass valve,

[cjizzle252]

the stock valve is a bypass/recirculating valve, it takes the pressure from right infront of the throttle body, and recirculates it back infront of the turbo inlet (j pipe between mass air flow and turbo) so it can be "recirculated" since the MAF has already metered this air. an aftermarket blow off valve dumps all your pressurized air to atmosphere, causing the engine to run momentarily rich, but reduces backpressure on the turbo resulting in longer turbo life, and a slightly faster spool time

[Jim Simms]

As the new engine will be installed, is there any advantage to having a blow of valve (BOV) installed off the intake pipe to the hose which goes back to the air intake hose between the fresh air intake and the turbo?

[Rocketman]

A blowoff valve vents to atmosphere, generally with an audible sound. You hear this as a "chhh" or a "whoosh" when you shift, or otherwise let off the throttle while building boost.

A bypass valve does the same thing, but as others have said, it recirculates the air so for the most part, you won't hear it.

Many of the modern valves can be both a BOV (vent to atmosphere) and Bypass (recirculate) Sometimes you need an adapter to convert the BOV to Bypass. There are many valves out there, and this will depend which one you choose.

The stock valve is the bypass type. It's not a very good one. It's also ~20+ years old at this point. (it has a rubber diaphragm inside)
Note: The stock bypass valve does not have a strong enough spring to be used as a BOV.

With our very small turbos, the performance is not really noticeable, but you can choose too large a BOV (not sensitive enough) or adjust it wrong (opens at too high a pressure) and damage the turbo in the long-run. Look up "Compressor Stall" for more info.

What it comes down to is mostly personal preference:

• Are you exceeding the limits of the stock bypass valve? (extra boost, larger turbo)
• Do you want the audible air discharge unique to turbo cars?
• Are you capable of doing minor/major fab work to install the valve?

Common BOVs
-HKS SSQV
-Greddy Type RS
-no-name piston style w/ 19mm hose barb, nearly direct fit to the factory piping

If you choose to vent your BOV you must block to return pipe

[Jim Simms]

Thanks so much.
Where does the hose from the bypass valve go? Where is it attached? It runs from the crosspipe to the bypass valve, then down "where"?

[Rocketman]

It returns into the plastic intake pipe on the turbo. It's a big "J" shape.

[Jim Simms]

Since the hose from the blowoff valve is connected to the J-pipe on the turbo, if you use a BOV would you have to cap of the J-pipe fitting on the turbo?

[Rocketman]

If you choose to vent your BOV you must block to return pipe

[Jim Simms]

I took all this great feedback from Rocket and others and studied my engine and it all is making more sense.

There appears to be three different places to vent the block:

1) at top of right of crossover pipe

The hose at  the far right side of the crossover pipe is a pipe, which is attached to a rubber hose, and weaves its way back toward the turbo on the right side. There it is attached to the bypass valve, which is attached by a small hose back up to the throttle and another hose to a downpipe below the crossover pipe.  Seems if a BOV is placed at this port, you would still have to connect to the throttle and the lower connection to the pipe below the crossover.


2) at top right of the manifold cover

This connection is a simple hose from the manifold cover to the second section of the hose, leading to the turbo. I have seen pics of small cone filters attached to the manifold, and also seen oil catch cans attached to this vent routing.

3) at the back passenger side where the PCV valve is located.

this easy enough to find. After reading tons of great postings on this matter, I saw that someone had put an oil catch can inline with the PCV.  It was not clear if the oil catch can was attached between the PCV and the motor, or after the PCV.  I am guessing BEFORE the PCV.

Also, at least one poster advocated using 2 oil catch cans; one at the PCV, and another off the manifold. 

That would leave the port at the top of the crossover pipe, where a BOV or a new bypass can be connected.

Am I on the right track?

[Rocketman]

The PVC / crankcase ventilation is in no way related to a BOV or Bypass valve system. So I'm not sure which track you're on

[Jim Simms]

I am referring to the two places on the right side of the motor: off the crossover pipe and off the valve cover gasket to put a BOV or blowoff.

I curious about thoughts of putting an oil catch can on either in line with the PCV or off the valve cover..

The question about an oil catch can being inline with the PCV is "where in line would you put it?"

[deewoody]

hello guys,
i am thinking my bypass air valve is not operating correctly. Only because i am not generating any psi over 5, and i dont hear the "mooing" sound nearly as much as i did before. I was able to get around 8 psi on my stock guage, very recently, and lots of "mooing". Not now, ever since i took a long drive, and while on that drive, i noticed that at high speeds (on the highway), and getting on it, at higher rpm's the car would "hesitate", while accelerating at high rpm's.
am i correct in assuming its the bypass air valve ?  If so.. does anyone have a good for sale?
thanks guys

[Rocketman]

Your wastegate could be stuck, or the turbo may not be spooling correctly due to damaged bearings. It could also be a torn diaphragm inside the stock bypass valve. You have a couple things to investigate