Why does air regulator pull air from J-PIPE?

[Sean73]

I have always wondered this. On stock L28ETs, the air regulator gets air from the ~1/2" nipple on the J-pipe. On NA cars, the air regulator gets air from the intake (after the afm).

 

Since the air regulator is only relevant during warm-up idle (off boost), then theoretically, it should behave the same on a NA car as a turbo car. So what explains the nipple on the J-pipe?

[yo2001]

because J-pipe is the intake on a turbo Z. And if you hook it before the turbo, under boost condition with the cold start valve open (This shouldn't happen if you are nice to your car) it'll actually suck air out of intake due to vacuum created by the turbo in the charge pipe.

[Sean73]

I see what you mean.

 

But with the air regulator drawing air from the j-pipe nipple, the turbo is forcing air into the air regulator at all times, and I wonder if this hampers flow out of the compressor by creating a turbulant area.

 

That's why I wonder about the alternative; running check valve between the intake boot and air regulator to prevent boost leaking out of the intake during the rare occasion that someone would run boost with the air regulator open.

[yo2001]

Sounds like a good idea. try and see if it works

[TimZ]

But with the air regulator drawing air from the j-pipe nipple' date=' the turbo is forcing air into the air regulator at all times, and I wonder if this hampers flow out of the compressor by creating a turbulant area.

[/quote']

 

At WOT there will be almost no pressure differential across the air regulator, so there will be virtually no flow through it. This is why it is plumbed the way it is. Moving the pickup point back to before the turbine inlet with a check valve will not fix anything (there was nothing wrong here in the first place), and will only add complexity.