BlkBird2000

iTrader: (10)

How do I figure out what spring I should have in my BOV? I heard something about having to know how much vacuum your car pulls at idle? I have a LQ4 with stock 317s and a tick stg1 turbo cam. I won't have the stock pvc system obviously. I'll be installing a mm catch can.

zapp109

iTrader: (13)

Gotta see where your car idles. Mine is -12 vac at idle so I got a spring that was rated for like 11-14 or something. But I was still having issues, I have the old 50mm tial and it was used. But anyway I then took the new spring cut a coil off and sanded the sides off the spring to make it thinner. Then the bov stayed open at idle so I put a washer in as a spacer and it is just closed at idle and bov works perfect. I know some guys run super soft springs and theirs is always open at idle and it works fine for them.

Sarg

iTrader: (6)

It will also depend if you are on maf or map tune as well as the placement of the bov. Maf with a bov hanging open after the maf is no good.

BlkBird2000

iTrader: (10)

Car will have a SD tune. The bov is located right after the intercooler. How do I figure out how much vacuum I have at idle?

tempoffroad

Just install a vacuum gauge off the manifold or vacuum block. You can get a gauge very cheep for this. My lq4 is around 12 -14 @idle.

Sarg

iTrader: (6)

Or scan it for manifold pressure.

ACCLR8N

I have one of those cheap plastic brake bleeding hand vacuum pumps. I connect the hose to a manifold vacuum source and read the gauge at idle. Then put the hose on the BOV and pump it down to the same value and make sure the BOV stays closed. Assuming you don't want unfiltered air bleeding in at idle.

In boost you have boost plus spring keeping it closed against boost in your piping. When the throttle closes, pressure drops and boost in the piping blows the spring open.