962s did not have an airflow meter.

How many of Porsche's turbocharged race cars had a blow off valve?

Exactly what I did to mine, or pretty darn close. Although I surely didn't do as professional a job (with nobody I could find to weld magnesium), I'm hear to say that the JB Weld is still holing strong.
Pictures....if anyone wants to see go here http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/518667-bov-update-short-neck-ic.html?highlight=neck+bov . Again, I set it up to recirculate vs. blow off.

This is the only picture I could find of the short neck 965 BOV setup sans intercooler. You can see the OEM 930 BOV was chopped off and a plate added to the end. That plate was modified for the OEM boost gage and overboost sensors. The OEM throttle bypass valve was retained to reduce burbling on decel. The braided line came off an Indy car and was for the cockpit boost gage. The WUR in this picture was made adjustable way back in 1995 and still performing well when this picture was taken a couple years ago.


http://forums.pelicanparts.com/uploa...1370667301.jpg

Going to try this week, disconnected the BOV from the "boot" last night, just need something to plug the hole and I am rolling....or maybe just use the OEM elbow. Regardless, I should be hearing the music in the next day or so....

Ok, so I am close to the music, but not quite there yet.....Disconnected the BOV from the elbow, plugged the elbow, and car would not idle. So I did some troubleshooting with the help of JFairman, and I am pulling 13inches of vacuum at idle, which is opening the BOV and venting sufficient intake pressure to atmosphere and the car will not idle properly. If I plug the Vacuum line car idles fine. So, my question is, 1) Should I be pulling 13 inches at idle, and if so, then apparently my spring (in the BOV) in not sufficient to keep the BOV closed at idle. Apparently this is ok when the BOV is connected to the intake elbow, as the pressure bleed is just vented back into the intake. Should I be looking for a different spring rate for the BOV?

Edit: I am picking up the vacuum for the BOV from the "T" right off the throttle body, where the other side of the "T" goes to the WUR.


tim

If you're using CIS a blow off valve vented to atmosphere can't be opening at idle.
If it opens at idle in the 965 type elbow hose it's sucking in air through the airflow meter so the right amount of fuel is being injected to go with it. Thats ok.

Your's is sucking in unmetered air at idle so it going way too lean. If it's a plastic bosch blow off/recirculation valve it uses a diaphram instead of a metal piston and it doesn't come apart to adjust it. There are different plastic bosch ones for Audi's, Porsche's, VW's or whatever and they look the same but have different part numbers and probably different rate springs inside.
An aluminum body brass piston type is better and they screw apart and come with shims to put under the spring so you can adjust when they open.

There are lots of them on Ebay last time I looked and there are a lot of good name brand ones that cost more. Depends how much you want to spend.

good luck with it.

Yeah I am running CIS. I have 13inches of vacuum at idle, (taken from one side of the "T" off the throttle body, the source for the vacuum line to the BOV) and I tested the BOV with a Vacuum pump, and 13 inches opens it up a large amount. So you are correct, at idle, with negative manifold pressure, the 13inches of vacuum is opening the BOV to suck in un metered air. So I am guessing, when I come off throttle between shifts, the vacuum will exceed 13inches, so do I need to adjust the BOV to remain closed up to 13-14inches of vacuum? How would one know at what vacuum the BOV actually needs to open???

The BOV is a billet one from TurboKraft.





tim

i just talked to timc and i have sent a message to synapse. i think we both may have our DV's connected wrong.
i have mine so that boost is pushing the piston closed and the spring is pushing it closed. this may be too much for the vacuum to overcome to open it. he says he has 13in of vac at idle but the spike in vac could over come the pressures keeping it closed just enough to open it, but how fast will it open like this?
i had mine this way thinking that the boost would help in closing it faster.

i am going to flip mine around tonight.
then i am going to try it vented to atmosphere. I WANT MORE FLAMES!
i would also like to try to set it up as a safety device to open under a certain amount of boost.

i should get my new WG today.... i hope.

like i told tim, i dont understand WHY RUF eliminates the BOV/DV? also, my boost pressure switch has been bypassed.

found this last night:


http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/419554-much-vac-bov.html#post4057652

13" of vacuum at idle is normal for a warmed up 930 motor because it has such low compression and that makes the motor relatively inefficiant and lazy until boost comes on.

By comparison 9.5 to 10:1 or higher compression normally aspirated motors are much more efficiant at idle and cruise speeds and they idle around 19"-21" of intake manifold vacuum because with higher compression in the cylinders they are making more heat and power with each power stroke of the engine with the same amount of air and fuel in the cylinder.

When the 930 motor or any other motor is decelerationg intake manifold vacuum immediately goes up to around 20"-25+" of vacuum depending on the engine rpms and how good the piston rings and valves are sealing when the throttle is closed.

You should adjust the spring tension in your CIS 930 blow off valve that's vented to atmosphere so it does not open until it sees around 15-16" of intake manifold vacuum. That way it will stay closed at idle and open when decelerating. You can test that with a mighty-vac tool.

Some blow off valves have a bolt and locknut to adjust spring tension and others you have to take apart and put shims under the spring.

The shims are usually just washers that fit under the spring and don't put them inside the piston on the piston side of the spring if possible because you don't want to increase the weight of the piston, that would slow down it's response a little.

That's interesting, and is Plan B, but, If I just flip the BOV around, so that the Piston is on the IC side, and vent the other side, it should provide the following:
1) Idle: Negative Pressure from the IC should keep the Piston closed.
2) Boost: Positive Pressure on control port should keep Piston closed.
3) Shifts: Negative pressure on control port, with positive pressure on piston should open piston to vent.

I'll try this theory tonight....

I have your 'billet" diverter valve, can that be adjusted to increase the required vacuum to open the piston?

I don't know what BOV you have so I can't guess what you can do with it.

I don't know what size turbo you have either. The AR or size of the hot turbine side of the turbo effects how fast the cold side compressor wheel will be spinning at idle and therefore how much mild positive pressure or lack of it there will be in the intercooler at idle.
Either way the BOV has to be shut at idle speed and steady cruise with an airflow meter controled fuel injection system or else unmetered air escaping or being sucked in at an open BOV will throw off the AFR. Only time it can be open is during deceleration.

1.The BOV spring is what keeps the BOV piston closed at idle.
2.Correct, boost pressure from the intake maifold on the control port of the BOV and the spring inside it work together to keep the piston shut during boosted acceleration.
3.Correct.

This sideways or backwards orientation is how I have my 25mm turboxs recirculation BOV installed in the 965 rubber elbow. It works either way but installing it sideways lets boost pressure push the piston open along with manifold vacuum sucking it open at the same time. I think it reacts faster that way but I'm not sure. All I know is it works smoothly and I have little turbo lag between upshifts.

The 32mm BOV I have under my intercooler can only be installed that way because of the horn on the side. The horn is threaded on and can be removed but I don't have a hose fitting to screw on in place of it and don't need one anyway.

Agree with you in design on (1), but I am hopeful/theory, that with the piston side connected to the IC, the Negative pressure in the IC at Idle, will overcome or counteract the Negative pressure from the control port to assist the spring in keeping it closed while at idle. I'll try this out tonight and let you know....

tim

If you have a small turbo it will be spinning fast at idle and making a little positive pressure in the intercooler at idle.

If you have a large turbo it will be turning slower at idle and you may have negative pressure in the intercooler at idle.

It's real easy to find out if you have pressure or vacuum in there at idle.
Pull the line off the intercooler that goes to the bottom of the wastegate to open it under boost and feel if air is blowing out or being sucked in while the motor is at idle speed.

So (1) did not work. BOV still opening. I also tried washers, but could still not make enough resistance to hold 13-15inches. I'll call TurboKraft tomorrow to see if they offer different spring rates.

No, different rate springs not offered for the billet 993T-style diverter valves.

Fyi. Chris and I have been talking and we decided not to go this route. I still encourage others to push the envelope...... Keep searching. Thanks

Who makes your DV?

Can I use this?

Fine tune your Blow Off/Diverter Valve to the exact needs of your engine.

I have a Forge on my SC turbo. Works about the same as the Audi valve I had. However, I am low boost (under 6 PSI), so you do get some adaptability on higher 930 type boost levels. I use mine as a diverter.