I'm getting ready to have my tial BOV welded on and I've heard that the springs are meant for piston engines and won't open properly with the rotary vacuum signal. My question is, at what vacuum should it start to open on a rotary? With a hand vacuum pump, I should be able to test the valve as it sits and either shim the spring or remove material from the spring until I achive the proper opening point.

 

the spring will make it more or less sensitive that is all. i don't remember how it works but i think a stiffer spring will make it less sensitive. its not a 2psi tipe thing it works off a pressure differential so at 10psi you could have it set off at a 1 or 2 psi drop after TB or a 10, 12 or 13drop after TB. but the stock spring shuld do fine.

 

I think I'm one of the few people who's TIAL BOV seems to work perfectly right off the bat. I have mine mounted right after the turbo, though.

It opens even with the slightest change in boost/vaccuum.

 

hmmm, I was under the impression that they opened when you were at x vacuum. If the spring is too light, it opens at vacuum that can be achieved by idle and you get a fluctuation and what not. Now if you get off the gas while in gear, you can damn near peg the boost gauge on the vacuum side. So that it only opens under such a situation. I'll do a little more research and see what I find.

 

The stock BOV opens at 300mmhg. That might help you.

 

Vacuum is vacuum, no matter what makes it. Rotary or pistom makes no difference at all.

If this is an open-vented BOV then you obviously don't want it open when idling. The actual vacuum reading doesn't matter, you just set it so that it doesn't open at idle.

The stock BOV is recirculating so it opens much sooner, and in fact is open at idle. You don't want that...