BOV confusion?

[nelsonmxmarc]

Well this is really interesting guys!
My car was backed into downtown montreal on saturday night so shes at my garage slowly being patched together..

Since it wont be moving for a while i think i'll try to tackle this..

As far as BOV's are concerned, i understand they need a vac source (intake plenum) and a recirc for dumped pressure (stock dumps back to turbo?.. and a/m like the second one i've got dumps to atmo?) At least from what i can see, that is what the large diameter tube is off the bottom of the stock BOV.. If i were to delete this, is there anything i should be aware of as far as things to be blocked off, such as the this dump pipe (black metal pipe). There seems to be a lot of clutter that can be taken car of deleting the stock BOV and at least running the A/M one for now until i change FMIC and charge pipes.

The one thing i haven't taken much notice of on the RB20DET is the turbo housing and bov setup so any tips or ideas on this would be appreciated!

I'll be taking the charge pipes off and removing the turbo housing shield in the next couple of days to check things out since, like i said, she's not going anywhere soon! And as far a block off goes, i can fab up a metal plate to kill the stock bov placement.

Thanks for the help guys!

[bobbo]

Sorry for the noob question but do the RB26s have two recirc bovs?

[Skym]

GTR has 2x BOV's in drivers side guard / front bumper area. Might be able to see the BOV's if you look through drivers side front vent on front bumper.

Vented to atmosphere is not recommended for factory MAF setup.

The reason why, is MAF has measured amount of air coming into intake piping and ECU is about to inject amount of fuel to match. If you remove the air behind MAF via BOV to atmosphere / engine bay, ECU has no way to know that the air was removed (except via 02 sensor, but only reads what comes out of engine / exhaust gas, not air which goes into engine), so can't compensate and injects the fuel to match amount of incoming air that it measured via MAF and engine runs rich.

With MAP setup it measures amount air at intake manifold (entering engine), so it doesn't matter if you have vented air to atmosphere / engine bay via BOV.

Factory BOV is a recirculated setup, so the air that's vented by BOV is sent via piping to intake pipe infront of turbo and reenters turbo thus keeping the same amount of air inside intake piping and engine doesn't run rich. Also vented air going back through turbo keeps the turbo spooling slightly faster, so engine / turbo responds quicker. You probably won't notice the performance difference unless you have tried both ways, but 1/4 mile time might drop due to just recirculating BOV (engine / turbo responds quicker after gearchanges). Also factory BOV is open at idle, so air is being constantly released to intake piping infront of turbo.

Factory BOV has a small hole next to main valve (bottom of BOV) for boost feed (boost pressure helps to open valve quicker) and vacuum feed from intake manifold to top of BOV which pulls open BOV under vacuum and helps to close BOV under boost. Some block the boost feed (little hole) to stop BOV leaking (did this on my car) but produces flutterdump (compressor surge), which is bad for turbo longevity hence why I was thinking of buying a Synchronic BOV.

On Synchronic BOV, it has 2 port's (A + B port's) for vacuum feed and one port (C port) for boost feed. It works like factory valve, but is pull type (pulls valve towards intake manifold to open valve). It stays shut under boost due to being a pull type BOV, which means the air from intakepiping piping going over top of motor is forced against valve inside Synchronic BOV, so valve doesn't get pushed open and leak under boost like stock BOV does. Stock BOV is a push type BOV, so main valve get pushed open under boost thus leaks.

Because Synchronic BOV doesn't leak and more air is getting to engine, there have been claims of 20-24hp increase in hp with this BOV and runs 1psi less boost due to turbo is not compensating for the leaking BOV.

Also Synchronic BOV has no diaphram, so responds quicker and vents air quicker thus reducing or eliminating the flutterdump sound when backing off throttle at lower boost levels. Flutterdump is a form of compressor surge, which is air hitting compressor wheel on turbo thus slowing turbo down, which is not good for bearings inside centre part / CHRA of turbo if turbo is constantly running at speed during acceleration, slowing down alot during gearchange and having to speed up after gearchange. Especially ballbearing CHRA, like found on stock turbo.

The Synchronic BOV is the only non diaphram BOV on the market that can be setup to recirculate for MAF setup or vented to atmosphere for MAP setup. A BOV with a diaphram can balloon and slows down BOV reaction time (valve opens slower) and get a flutterdump sound. Changing springs or tightening BOV helps to reduce this, but also causes BOV to leak.

Sorry about the long post, just thought it might help to understand how the stock, etc BOV's work.

[nelsonmxmarc]

Amazing post man! Well put. Should put this up as a sticky; i'd assume only a handful of people truly understand the true purpose of a BOV vs. the fantastic sounds it creates.

After our previous discussion i went ahead messed around.. My first mistake was assuming the RECIRC went back to the housing, upon further investigation i realize it dumps directly into the intake neck right by the PCV dump.

I also went ahead and removed my "secondary" BOV, which turns out to be an old school HKS 'Super blow off valve' and swapped charge pipes to rid of its outlet. This thing made the best wooooooosh i have ever heard in the department of BOV's and i kind of wish i had taken a video, but from researching the past view days, i've also recognized its flaws. For 1. i believe the spring tension was so soft that it was actually bleeding air about 90% of the time, thus creating a very high "squeeling" sound when cruising at about 100 km/h. 2, i also noticed that even by maxing out my profec b spec 2 in all respects, continually yielded 14.5-15 lbs of boost. Not that i was aiming for more, but i suspect that it was bleeding off so much pressure that boost levels above this were unattainable.


Haven't driven it yet unfortunately but it's going to Autoworx tomorrow morning to see about a quote for paint and minor body work; can't wait to see how it is!


Skym..

I read a post this afternoon about BOV's in the GTR tech section from a while back where you were talking about synchronic vs other. There were various videos of off-throttle compressor surge with cars running stock BOV's with the boost feed plugged, and also no bov's and etc. You mentioned that this off-throttle chatter isn't bad ONLY if it's a ball bearing turbo, or a larger turbo that's built to either take the abuse or is meant to reduce surge?

I also read somewhere in that post (can't find it now, dammit!) that the stock turbo isn't likely to give out based on your driving habits (shift quick to reduce loss of pressure feeding back into the turbo) so it is safe to say that the stock turbo is capable of running well without a BOV, or is it less of a hassle in the long run to run the RECIRC and play it safe? Or better yet, as you did, plug the feed hole on the oem bov and run it that way? I plan to keep the stock turbo but like we went over in Klys' build thread, i plan to change housing and turbine to "bore" it out in the end to keep the low end spool. Yay or nay on the plugging the hole in the long run?

Thanks again for the fantastic info, im not sure what i'd do without you guys! hah

[bobbo]

WOW! Thanks Skym! I love detailed explanations. I was going to get a set of the synchronic bovs but only because the concept seemed to be the most advantageous. I didn't realize that you could actually reduce the cars performance by simply going to an a/m bov. If the synchronic bovs can be used w/o negative side affects and can actully improve performance then it's worth the $500+.
Thanks!

[Skym]

I think to save $$$, some run a big single BOV (bigger valve to compensate for lack of opening quick enough to vent air) on GTR, like Type R BOV from Greedy / Trust and flange setup that plumbs into stock intakepiping. They sell Greedy BOV flange for Synchronic BOV, so might be able to use 1x BOV and Greedy / Trust flange setup as Synchronic BOV is said to vent better than a bigger BOV.

This R32GTR with big single (600hp at engine) has Synchronic BOV's -

http://www.youtube.com/watch?v=VM_og71DCyw

Driving on the road with above 600hp R32GTR -

http://www.youtube.com/watch?v=IP0IV0sZgHE&feature

If Synchronic BOV works on a 600hp GTR, shouldn't have problems with my car or your cars.

Alot of problems are due to plumbing Synchronic BOV incorrectly or damaging O rings or not tightening set screws properly, etc (installation problems). Or in some cases the BOV is faulty from factory (rare). Might be worth investing in longer set screws for flange, as shown via photo in this thread -

http://www.dsmtalk.com/forums/showthread.php?t=202213

Nelsonmxmarc, bigger turbo shift's more air at same boost level compared to stock turbo, so should make modified BOV valve (has a weaker spring) lift at lower boost levels. At least that's the theory.

Turbo's that are non ballbearing can take the abuse of a BOV not working properly or not there at all.

Let the stock BOV leak with ballbearing stock RB20 turbo until it can be sorted properly with Synchronic or similar BOV.

[Skym]

Add to that list a 908whp Supra with Synapse BOV's and more than 34psi boost -

http://www.supraforums.com/forum/showthread.php?p=7021602

[bobbo]

I've heard there has been alot of problems with these. Do you know if this is because there are too many "know it alls" installing them wrong or is there developement problems?
Also if you only have to use 1 bov on a GTR is there an adapter plate available or is this something that one would make?

[Skym]

That's what I've seen in some cases where it doesn't work.

In one or 2 cases I've read about, BOV leaks where it shouldn't leak (very rare). Customer sent back leaking BOV. Manufacturer provided good service by sending another BOV that didn't leak. I think some other leaking BOV problems are related to breaking O ring on flange during installation (not lubing O ring as per instructions provided by manufacturer, before installing on flange or fitting flange into BOV).

On some cars the Synchronic BOV is a bit more difficult to setup properly. I presume the reason why, is there are vacuum blocks, etc that affect getting a clean feed of air to BOV. Not so on Skylines, as they use a very basic BOV setup with a clean feed of air from intake plenum. Also longer vacuum hoses to BOV could slow down the reaction time of any aftermarket BOV, including stock BOV (vacuum hose to vacuum block from I think is intake manifold and vacuum hose to BOV from vacuum block). In one case I saw, plumbing vacuum hose from intake plenum to I think was port A only on Synchronic BOV (like you do with factory BOV) fixed the problem with BOV not working properly.

The interchangable flange part of Synchronic BOV gives the BOV a weak spot when running higher boost levels. Designer added a V part in middle of BOV to put a cable tie (or similar) through and wrap around intakepiping to help in keeping BOV from popping off flange. But he says this is used when BOV is placed on weird angles, like upside down or on it's side. This is the only design flaw I can see.

But one case I've heard about BOV popping off flange, I think one of the set screws fell out (I presume set screws are not tight enough or long enough) and BOV popped off the flange (I presume the left over set screw ripped through and damaged O ring, scored flange, as they were replaced). Never seemed to do it again after he fitted new flange, O ring, new set screws.

Another case I read about where BOV popped off flange on racecar, was when running higher boost levels with a big turbo. He eventually welded a Tial V band flange setup to BOV. Never had BOV popping off flange problems after that fix. The high hp, high boost levels on Supra, R32GTR in videoclips above, show that it might have been another case of not tightening set screws properly or set screws are not long enough.

Apart from the above problems, BOV works as advertised.

Greedy / Trust might still sell the single BOV flange setup for GTR. Or probably could find one second hand if they don't sell it separately.

Another option, might be blocking off one BOV flange on stock GTR BOV setup and using the other flange for Synchronic BOV. If you find it's not venting enough air, buy another Synchronic BOV and fit it.

[bobbo]

Quite interesting. I wonder why Nissan would fit two bovs if they weren't required. Usually manufacturers will keep things as simple/as cheap as possible.
That being said if the 600hp GT-R in the vid works fine with one, where I am one bov should be fine aswell.
Thanks for all the additional info!
btw, where is "south"?

[M13]

Quite interesting. I wonder why Nissan would fit two bovs if they weren't required. Usually manufacturers will keep things as simple/as cheap as possible.
That being said if the 600hp GT-R in the vid works fine with one, where I am one bov should be fine aswell.
Thanks for all the additional info!
btw, where is "south"?

ROFL

[bobbo]

I hate you so much!!!!
Remind me if I ever have to navigate somewhere specific to get in touch with you.... ass!
... and in case you didn't notice I put south in quotes because he says that's where he is and I was curious... you tit

[nelsonmxmarc]

hahaha

[Skym]

The stock BOV's still have diaphrams, so are slower to react and vent enough air. Designers at car manufacturer back in the 1990's probably thought 2 x BOV's would solve the problem. With Synchronic BOV venting enough air quick enough, probably only need one BOV. Alot of BOV manufacturers seem to use valve size to compensate for slow reacting BOV or modify the diaphram design. They don't seem to solve the problem, which is using a diaphram.

The dude from Synapse in this videoclip below explains how a diaphram affects the opening of external wastegate and how slow opening causes boost spikes. Also how their wastegate works without a boost controller with multiple boost settings -

http://videos.streetfire.net/video/SEMA-2006-StreetFirenet_82377.htm

Here's another videoclip, where the dude from Synapse shows on a graph, how quick the Synchronic BOV opens and vents 37psi worth of air. Also how the different ports affect BOV operation -

http://www.youtube.com/watch?v=71L1w77xC-M

Also HKS BOV is pull type BOV. But as far as I know it still has a diaphram.

South refers to south of the equator or some call downunder. Maybe I should change to downunder???

[bobbo]

South refers to south of the equator or some call downunder. Maybe I should change to downunder???

Safe to assume Australia then? There's alot of earth under the equator.
Anyway, again thanks for the bov education. It's appreciated.

Rob