Can I bleed the BOV to Atmos..with CIS
 

Getting closer on my 964 3.6 L hotrod complete build. The long block has been finished and now on the the plumbing. I would like to bleed the BOV to atmosphere because I like the sound it makes... I know...it is a little cheesy... I drove a Ferrari 458 Twin Turbo that Underground Racing built and really enjoyed the BOV sound. Also, any ideas for BOV locations other than stock. Any information is much appreciated. Thanks

the short answer..... NO...

The long answer, If you vent that air to atmosphere, instead of recirculating it, you will be under a rich condition since that air is/ has been metered by the air flow plate, and fuel has been added in direct relation to how much air there is...

I guess you could... but unless there was a performance asspect to it, I wouldnt. I would also say that its not all the time that the BOV is open (just on decel, when there was boost present), so if you did vent to atmosphere, it would not be for very long.

BTW, If I have never told you.. I am jealous of where you live... it is so beautiful up there!!

if it is mainly used on decel, and it goes rich, might add to the flames out the back!!!

wish i had a BOV. i have a synapse DV that i have been thinking about re-routing as a BOV, might even vent to atmosphere, besides, the extra fuel on decel might cool things off a bit.

not a fan of the RUF conversion, they removed the BOV. nothing to prevent overboost. not mention i was concerned that if there was a spike in boost when letting off the gas could be hard on the WUR diaphragm.

Didn't we go over this yesterday?

I've got a BOV that dumps to atmosphere, no issues so far, but to be honest I've only put a several hundred miles on it since the conversion.

Yes you can, and yes it will make a richer mixture at first because air flow meter metered air is not being recirculated back to the turbo inlet. The motor will blow or pop flames out the exhaust depending on your muffler design or lack of muffler because of the rich mixture on deceleration.

If you decelerate continuously for a little while like going down a hill or from high speed then depending on the the size of the hot side of the turbo it will slow down enough after 4-6 seconds to the point it is not making more airflow or turbo air pressure than the engine is taking in and then positive pressure in the intercooler will gradually turn to vacuum and the open BOV will start to suck in air so put a small k&n air filter or something similar on it so the motor is sucking in filtered air and no dirt or dust through the open BOV.

I have two blow off valves because I like gadgets and the chinese ones on ebay are inexpensive and some of them are precision made and work great.
A 25mm turboxpress japanese made one recirculates to the 964 type rubber elbow hose and a 32mm back anodized one vents to atmosphere under my intercooler. I have a small stainless steel mesh air filter on the 32mm one.

I like the little woosh sound of it when letting off the gas between boosted upshifts too and I put a little air valve on the vacuum line going to the 32mm BOV vented to atmosphere so I can preset or control the opening bias between it and the recirculating BOV. I know it's silly but I like it.

and,
I can always remove it!

Everybody has covered it pretty well. Generally speaking most would say don't do it, due to the rich spike it will cause, but a lot of people do it anyway I think...if not for anything but to get a woody when she 'whistles' between boosted shifts.
Not that it's damaging or anything, just goes pig rich when you jump off the throttle to shift, plus you lose the volume of air that in a normal recirculation valve setup would still be available when it comes time to get back on the gas and boost her up...supposedly resulting in less turbo lag.

I ran an open BOV on the red rocket, loved it! Flames on decel and cool sounds.
My system was minimal CIS so I simply ran the BOV off the AAR port of the intercooler. A long neck adapter was made from the 930 BOV.
No harm no foul; I didn't find any reason not to do this other than my license plate turned tan from the heat.

http://forums.pelicanparts.com/uploa...1370578695.jpg

There is no increase of turbo lag venting the BOV to atmosphere like mentioned by someone thats never done it.

With two small BOV's, one recirculating and the other venting to atmosphere compressor surge is reduced compared to just one small one recirculating so the turbo can keep spinning faster when you lift the throttle between boosted upshifts and that does just the opposite, it reduces turbo lag when you get back on the throttle.

The AFR goes richer at first when lifting and thats what makes the flames and when decelerating for stretches longer than 3 seconds the mixture actually leans out more than it would recirculating as the blow off valve is held open by high intake manifold vacuum and it starts inhaling air into the intercooler as the turbo spools down.
This is what I see on my AFR gauge using a k27 7006 or the k27 7200 HFS thats on my car right now.
Then when you get back on the gas the AFR immediately jumps back to normal and I don't notice any difference in throttle response. Just nice sounds.

I like how it works and sounds. Recirculating BOV's are boring.. ha!

Brian,

How do you have yours plumbed?

I ran my 77 930 for 10+ years with the BOV going to atmosphere. its fine, it goes richer for a second under decel, helps with flames, and helps cool the heads when your really enjoying the car.
no issues.

I stand corrected. I was thinking compressor stall if one didn't have a BOV when I wrote that. I believe that's what BOV's are for in general, recirculating or otherwise, to prevent compressor stall. Gotta get rid of that compressed air when the TB slams closed at shifting. If I'm not mistaken, the Porsche engineers went with recirculating more to handle the rich conditions that occur when venting to atmosphere...I'm guessing probably to meet emissions requirements. If a person had no BOV at all, then the stall (besides causing stress on the turbo) would lengthen the time needed to spool back up by some margin.

When I removed my recirc manifold and installed an aftermarket (Chinese) BOV it was build to do either/or...and I chose to plumb it in as a recirc valve. It would be a simple matter (well, nothing's simple) to re-plumb to vent to atmosphere. Perhaps I'll try that some day, maybe get some cool noise and some flames!

2nd!

weekend project muwhahahaaa 8-) Improves my flamingness eh? Hey wait a sec.

Sir B, so you installed the 710N (think I've got an old Audi one on the shelf still go figger) - and retained the OE integrated slapping spring-piston unit? Is it really that simple? Care to handhold me like you did when I did my intake vent plumbing? Damn, whattapal you are!

I know Mark cut his out (OE BPV), that may be a winter project here @ some point heh heh, and Petey's ran who knows what for that there but ohhhh did his car sound guuuuuuuud.

Jimbo, your setup seems neat, bet it's a hoot - pics / tutorial for the ingnoramus? 8-)

Plumbing on mine was very simple as most of the CIS was deleted. The OEM 930 BOV was not retained but rather cut up and used as an adapter to connect all the sensors as before the change. That's it. I can post a picture with the intercooler removed so you can see what was done and decide if you want to give it a go.

I just spent an hour writing a long post with pictures of my BOV's included and pressed backspace on the keyboard by mistake and lost it all... i'm really pissed now and have to get away from this f..... computer.

i'll rewrite it all later.

btw, the CIS deceleration valve is a second small blow off valve that vents into the intake manifold instead of between the air flow meter and the turbo intake.

OK great thanks B! That's what I thought, have to resection the recirc mani.

BEGONE! I say...

pics would be teets - UDAMAN - Mark'd shared his w/ me but that was manymany (many) moons ago

winter project then... sweet

D'oh!!!

sorry to hear that Jim... I've soooooo btdt before... sooooooooooo frustrating!

thanks for trying, looking forward to what it was should you be fewl enough to re-indulge us! 8-)

I won't try to rewrite everything I thought of before but here's a couple 2 year old pics of my second 32mm BOV that lives under my intercooler.

I use the intake manifold vacuum line from the throttle body that operated the deceleration valve tee'd off to open both of the BOV's and a little brass air valve to control how fast the vacuum hits and opens the black 32mm BOV in relation to the 25mm turboxs recirculation BOV you can't see in these pics.

I think the 25mm recirculating BOV in the 964 elbow hose off the air flow meter is dumping most if it because of how I set that little brass air valve I soldered to the brass vacuum tee, but thats just a guess.

In this pic I have a vacuum solenoid in the vacuum line going to the black BOV so I could disable it from inside the car for comparisons. I've since removed that and they both work all the time.

I started out by venting my good working deceleration valve to atmosphere under the intercooler with the same stainless steel mesh air filter on it but it's small, unadjustable, and ugly so I sold it for $40 and bought this 32mm black anodized adjustable one off ebay for around $35. It's been on there working fine for a couple years now.
I have one of the spring tension washer shims they give you under the piston spring in the black BOV and I greased the spring and brass piston to keep it lubed in it's cylinder.
The small stainless mesh air cleaner is silicone glued into the air horn on the black BOV so it filters the air that is sucked in after decelerating 3-4 seconds or longer when the turbo slows down enough that boost goes away and turns to vacuum inside the intercooler.
The nicely machined aluminum horn is threaded so it can be removed and replaced with a hose fitting. It's only there to make the throttle lift woosh noise a little louder.

I ground the Kokeln Racing label off the intercooler end tank and polished it with air tools.

http://forums.pelicanparts.com/uploa...1370625763.jpg
http://forums.pelicanparts.com/uploa...1370625777.jpg

Here's a couple more recent pics and you can see the second BOV fits under the intercooler nice.

Hose clamp city on the blue throttle body air bypass hose because I also have another 10mm vacuum solenoid from an old L-jetronic 6 cylinder BMW bypassing air around the throttle body in that hose that opens when the AC compressor comes on to keep the idle from dropping around 2-300 rpms when the AC compressor kicks on. It's mounted on a little bracket back around on the side of the air flow meter.
With it working idle speed stays exactly the same when the AC compressor clutch engages now.
http://forums.pelicanparts.com/uploa...1370627778.jpg
http://forums.pelicanparts.com/uploa...1370627790.jpg

didnt the 962's vent to atmosphere?

i would like to try it with my sysnapse DV. can i and how do i. does it have to be adjusted to open at a certain boost PSI.

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.