Can I bleed the BOV to Atmos..with CIS

[AskewRSR]

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

[turbobrat930]

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!!

[T77911S]

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.

[TurboKraft]

Didn't we go over this yesterday?

[gavinc69]

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.

[JFairman]

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!

[mark houghton]

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.

[RarlyL8]

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.

[JFairman]

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!

[sundevil64]

Brian,

How do you have yours plumbed?

[pkracer21j]

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.

[mark houghton]

Originally Posted by JFairman

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

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!

[krasuskyp]

Originally Posted by sundevil64

Brian,

How do you have yours plumbed?

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-)

[RarlyL8]

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.

[JFairman]

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.

[krasuskyp]

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

[krasuskyp]

Originally Posted by JFairman

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.

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-)

[JFairman]

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.

[JFairman]

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.

[T77911S]

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.