Thread: BOV orientation
View Single Post
JFairman JFairman is offline
Registered User
Join Date: Jul 2006
Location: S. Florida
Posts: 7,274
The one on the left of your pic from your post above looks alot like mine, accept mine doesn't have interchangeable fittings on the one end.

The black rings on the top part are orings in the grooves for cosmetics and getting a grip on it to unscrew the top or adjust spring tension.
There's another important oring on the inside to seal the top to the frame even if it is partially unscrewed to lighten spring pressure.

The brass piston in mine is hollow and about 2" long and the majority of the spring is compressed inside it.
The piston doesn't get wider at the vacuum line end so surface area that boost pressure will push against is the same on both sides of the piston but there is a chamber 360 degrees around the sides of the piston just above where it seats so that would improve air flow through it when the piston is off it's seat and the BOV is open.

Here mine installed sideways:

The blue hose goes to a fitting on the back of the intercooler.

When Porsche first made the 930 in '75 I don't think there were any small lightweight blow off valves available like there are today, It was early street car turbo development so they made what they did and it is probably bigger than it has to be.

I don't have a vacuum gauge in the car but I've hooked one up at idle and my car idles at about 15" vacuum.

I also reinstalled my deceleration valve on the hose fitting made for it on the back of my intercooler and have it venting metered turbo boost air pressure to atmosphere when letting off the gas along with the BOV recirculating air into the big rubber hose.

The deceleration valve opens at 5" higher manifold vacuum than the TurboXS BOV so it opens after the BOV and not completely unless you're decelerating at speed in gear.
The decel valve's exit hose connection is only 7/16" inside diameter so it doesn't flow any where near as much air as the BOV.

Last edited by JFairman; 12-08-2009 at 10:42 AM..
Old 12-08-2009, 10:30 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #7 (permalink)