Variable boost / bov settings
 

A lot of the EFI controlled cars here have variable boost settings. Usually either street versus track maps or e-85 vs premium gas maps. My question is what about the BOV if my waste gate opens at 1.3 bar on premium and 2 bar on e-85 shouldn't the BOV be opening at around the same pressure? or should the springs be set to the highest possible boost levels?

You want the lowest spring and then let the boost controller manage pressures above that.

I understand that with the waste gate. But my question is the BOV. Those are never connected to the boost controller so should the spring setting be the same as the highest boost?

I was under the impression the BOV opened when the throttle plate closed, to relieve pressure from the turbo. Mine is not adjustable, (965 type) but always wondered what benefit there was to having it adjustable? Philip

It does open when the throttle plate is closed and you set the presure at which it opens by changing the spring in it. I just wanted to make sure i pick the right spring so that it's not opening while on boost and when the throttle plates close the pressure isnt so high that it stalls the turbo.

Sorry, miss read the post. You want to make sure it doesn't open at part throttle, idle, or low vacuum loads. The boost will keep it closed no matter what the spring rate is.

Whats yours set at? and whats your boost setting?

I'll have to look but as I recall it is the plain spring on a 50mm Tial so -10 spring rate. My idle vacuum runs a MAP of about 40, max boost so far is 1.2 but currently under 1 until I can get the e85 sorted.

With your high flowing individual throttle bodies you'll have less boost pressure drop through the throttle bodies on the intake side below them during boost then with a single throttle body and plenum chamber so the vacuum side of the BOV piston where the spring is will be seeing almost the same positive pressure as the business side of the BOV piston.
Therefore the BOV standard spring pressure should hold the BOV shut during boost. You can experiment with shims under the spring or try different springs to test reaction time of the BOV in relation to throttle positon and boost/off boost transitions.

On another note I think your brake booster vacuum line should be connected to only one intake runner.
When I had a BMW 2002 with dual sidedraft Weber 45 DCOE carbs thats how it was set up. At the same time it was 4 seperate carbs that had to be synchronized to idle smooth. One 45mm carburator throat and butterfly for each 500cc cylinder and not EFI so maybe that doesn't correlate.

I'll have two manifolds that I rout the vacuum lines from each cylinder too. One just for the brakes. The other for idle bleed, vacuum signal to the boost controller and bov's etc.

I might get some sh#$%$ for saying this but you should run a real BOV, The bosch (plastic, non adjustable, rubber diaphram, weak spring=junk)stuff is barely adequate and a lot of people just don't realize how important that little device is and how adjustments can really affect things. Even an old style Greddy RS valve is night and day superior over these little factory cost savers...

was planning on using turbosmart BOV's and wastegates. This time around and wondering which spring to get with the BOV's. Since it's twin scroll with my own fabbed intake plenums there will be two Waste gates and two bov's

Turbosmart makes some very nice ones. I used to run both on a twin turbo 928 I built years ago. Good choice. Also the 965 elbow is really not the best option even though people believe it is because the factory used it. The BOV is better placed on the charge pipe right before the throttle body. It does make a difference there even if you run it back to the 965 elbow to dump. I prefer it open as I like the sound:D Some even bung it off the outlet side of the IC although I never have. JFairman Gave good advice above if that is your set up he is referring to.

And those inexpensive factory nylon diverter valves are better than most of the bolt-in replacement aftermarket billet diverter valves. :(

Can't go wrong with Turbosmart wastegates or blow off valves.

ok so which BOV should i get the one with the 7 pound spring or the 14 pound spring?

I would agree Chis if we were talking about their intended purpose on a stock car sure. Get the BOV Ken, the adjustments are very wide in stock form. Unless you are planning to run over 25-30 psi..AND AS JF mentioned above I believe you can shim for further tension but that is stratospheric boost for 930's. just install it, run it open or closed and experiment with the settings while you are boosting the hell out of it. You will find the sweet spot