Dual Bov Recirc + Atmo And The Results...

[CEF11E]

I have been running a standard BOV on my R32 GTST and it does a really good job. I had noticed with the hiflow turbo and running 19psi on hard up changes it would "bounce" causing a slight hesitation on acceleration. I did not want to go an atmo BOV due to the silly noise and stalling issues and over fueling on gear changes so I came up with the idea of running both.

The factory BOV remains intact and in complete normal operation. I have welded a flange on the underside of the downpipe that connects to the intake pipe that connects to the throttle body. Here the Blitz supersound BOV is connected I have set teh opening pressure to 14psi using a mittyvac.

This means for normal driving and boost levels of up to 1bar the normal BOV works without interference so there is no loud noise and no over fueling. Once a boost level of 14psi or higher is reached the ATMO BOV is "armed" and will function as soon as the throttle is closed. and you do get a loud pchttt. I can deal with this because the last thing you are worried about at 19psi and 240kw is silly BOV noises.

The results are a much more responsive car to drive. On hard changes when you get into the next gear boost is instant and there is no hesitation. it picks up right where you left it in the last gear.

so you get all the benefits of a stock BOV with the added bonus of extra throttle response.

I know there are 50/50 atmo/recirc BOV's available but in my current configuration teh installation looks factory unless you really go looking for it and i don't like engine candy I much prefer a completly standard looking engine bay.

[R31Nismoid]

Good result Sounds like the little BOV wasnt flowing enough.

Or maybe the VAC line wasnt large enough.

Nice way around it.

You could also try a single GTR BOV. I used one with my setup over 300rwkw/24psi and it worked a treat with a nice big VAC line going to it

[Strik3r]

1 question - when you hit over 1 bar of boost and therefore use your atmo BOV, dont you still get the over fuelling / stalling issues ??

[paulr33]

nice work

[jeffworld2]

you dont stall easily at the revs needed to get 1 bar, i assume.

[CEF11E]

the overfuelling at 1bar would still be there i assume but at that sort of level it can actually be useful. because when you get the next gear you will be at peak torque and the little extra fuel acts as a detonation suppressor. this would be easily tuned out.

I have not used a wideband to check it yet. it would be less than just an atmo would give as a large percentage of air is still going thru the stock BOV.

[MANWHORE]

I really don't understand why people think one gtr bov is better than an r33 gtst bov.

Comparing my r32 gtst bov to the r33 one, it seems that the r33 setup flows more, because it seems to release pressure quicker, whereas the r32 unit has a longer psscht.

But the gtr unit seems to be the same size as the r33 bov?

do they actually flow more?

I have no doubt that the pair of them would flow more, but keep in mind, a gtr has two turbos, which are smaller than the r33 gtst turbo. I assumed that the gtr bov flows less, since it's deisgned to release pressure from a smaller turbo?

[R31Nismoid]

I was under the impression GTR BOV is not the same as an R33 one as i was told to get a GTR BOV and not a GTS-t one.

But then mine could have been modified

[Craved]

i really like this idea some more info on the mittyvac would be helpful.

i was planning to run a plumb back and a atmo simultaneously, but this idea sounds alot better

[MANWHORE]

what do you want to know about the mityvac? It is basically a vacuum pump, like what you use on a penis pump... squeeze squeeze, squeeze.

It has a guage on it and you can either use it to vacuum, or blow.

I find them really good for doing things like testing actuators, like bovs, wastegate actuators.

I also use it to bleed brakes. Has a cup, whcih you hook the line onto the nipple, and pump (no joke intendeD).

I'm guessing that what cef did, is pumped the mityvac up to 14psi, and set it so that the bov is triggered at this pressure.

Edited February 22, 2007 by MANWHORE

[MANWHORE]

I was under the impression GTR BOV is not the same as an R33 one as i was told to get a GTR BOV and not a GTS-t one.

But then mine could have been modified

Oh ok, I'm not sure mate, I was hoping that you knew, so I was asking you since I knew you were running a single gtr bov

From what i was told, 1 gtr turbo = smaller than gtst turbo. 1 gtr bov smaller than gtst bov.

I'd like to know whether it's true that the gtr bovs are better, or if it's really myth

[Craved]

what do you want to know about the mityvac? It is basically a vacuum pump, like what you use on a penis pump... squeeze squeeze, squeeze.

It has a guage on it and you can either use it to vacuum, or blow.

I find them really good for doing things like testing actuators, like bovs, wastegate actuators.

I also use it to bleed brakes. Has a cut, whcih you hook the line onto the nipple, and pump (no joke intendeD).

I'm guessing that what cef did, is pumped the mityvac up to 14psi, and set it so that the bov is triggered at this pressure.

ahhh that explains it well.. from my google search i sort of got that gist, but i was thinking that it might have included some kind of actuator that only opened once the system went to 14psi which activated the vacuum line to the atmo BOV.

[CEF11E]

No there in so actuator.

you could use one. a turbotech boost controller or a check valve set to 14psi would work.

The other thing I have noticed is. The blitz BOV connected by itself makes a lovely compressor killing noise wooo wooo wooo woooch at low boost. now with the twin setup there is no surge.

[Craved]

No there in so actuator.

you could use one. a turbotech boost controller or a check valve set to 14psi would work.

The other thing I have noticed is. The blitz BOV connected by itself makes a lovely compressor killing noise wooo wooo wooo woooch at low boost. now with the twin setup there is no surge.

i think i'll be giving this a go

now to find my old std BOV

[CEF11E]

I have been doing some tuning and have noticed there is no change in the AFR with the atmo letting out the small amount of air. this was measured with a lambda and data logger.

after a bit of fiddling i had settled with the atmo opening at 1 bar and opening to about 40% of its capacity. it is adjustable and allowing it to vent anymore does not improve response time.

in between changes it is a clean split second Pccct. and as soon as you get back on the throttle you are right back at full boost.

if i close it further you start to notice a lack of response. so i have found the optimum rate of discharge.

Not sure if this is for everyone as it requires a bit of fiddling to get correct but there is defiantly benefit in tuning your BOV/S to suit your mods and boost level.

[DJRIFT]

hmmm id decided to just keep the stock bov running but then id heard that the stock bov would only hold back around 14psi so i thought if you went further 19psi it would just be venting all the time. so if i went for an aftermarket bov id get a plumb back was my thoughts, which im getting a greddy old type s which can be made plumb back but i think aftermarket plumb backs still make the flutter noise you are talking about. i was also going to change my cooler piping to get rid of the factory throttle intake pipe but maybe after reading this i will have a look at doing the same.