BOV Recirculating or Atmo. Mixed opinions!

[nickch]

have been searching on here relating this issue as I'm pondering on which path i should go down with a V7 WRX.

See this post here: http://www.clubsub.org.nz/forum/index.php/topic,6535.30.html

outcome from my understanding is that a recirculating BOV is considered 'better' but the debate (see link above) was that the difference between recirculating and atmospheric discharge is minuscule. (point being that the air is slightly colder and it cools the intake air for a split second)

then theres mention everywhere online regarding a plumb back for WRXs as the MAF adjusts itself for recirculated air and that discharging it to atmo would cause the engine to run rich.

Now, I've read about this in a lot of places, but I've also read about people mentioning that they have no problems whats-o-ever discharging to atmo. Which is more accurate? Is there something you could do to mitigate the motor running rich during this phase?

Any input/debates/discussion welcomed.

[Guest]

Atmos BOV

Car will run richer - might get the occasional pop from the exhuast from the unburnt fuel.

The AFM has metered the air and the ECU doesn't know its been released to atmosphere lol so there is no practical way arround it. Unless you buy a speed density ecu which seems overkill for just that reason.

It will make more noise - and thats the main reason people get one otherwise why would u bother.

[Pappu1]

if u want the max noise then get a atmo bov (ecu wont be as happy but not too bad in the general scheme of things)

if u want noise but also prefer to have the plumback to keep the factory ecu happy then get a GFB wrx hybrid one - they have the option set to plumback and have atmo for some noise - best compromise

if not for noise then leave the factory v7 valve in place (they are seriously good stuff)

[nickch]

currently, depending on which path i go down i've narrowed down my choices to:

recirc: Synapse Synchronic

atmo: Tial 50mm

while am keen to give the synchronic a try, i like the sound of the Tials..

if recirculating is only considered 'best practice' and having atmo would not cause too many problems, i will go down the atmo path...

[dubbedup]

I have never used a recirc BOV, and have had no probs running rich for that split second, IMO if you gunna use a recirc bov you might as wel save money and leave the factory one in there.

[pl0x]

 dubbedup said:

I have never used a recirc BOV, and have had no probs running rich for that split second, IMO if you gunna use a recirc bov you might as wel save money and leave the factory one in there.

agree

ive used factory then changed to 50% (50/50 GFB) then set the gfb to 100% vent and pretty much no difference. few little exhaust pops now and again

[Guest]

as long as the bov dont leak, there all the same really.

if on a standard car, venting to atmosphere when the valve opens it does not put the air into the system, this causes the car to run rich for that shot amount of time. as the airflow meter monitors the air, and know that x amount is put in from the bov. but its not there so theres more petrol than oxygen.

if running an aftermarket ecu or chip that does not require the AFM, then this is not an issue

-smurff

[Stoffa]

I believe its actually illigal to vent to atmoshere now, you may pass a WOF ok but you'll probably get failed on a LVV cert

[mazdahard]

 Stoffa said:

I believe its actually illigal to vent to atmoshere now, you may pass a WOF ok but you'll probably get failed on a LVV cert

since when?

[Pappu1]

all the TIAL ones i have heard flutter a lot on lower boost so wont really recomend for u man.. unless u love that sort of sound..

the Tials i heard were mostly on evo and few skylines so may not even have been genuine ones but the trademe versions hence the pathetic performance

[nickch]

The one I'm looking at is

http://www.trademe.co.nz/Trade-Me-Motors/Car-parts-accessories/Performance/Turbos/auction-272802630.htm

There are a few vids of WRXs with them. But yeah, there was a bit of stutter and I assumed that the poster must've not installed it properly. It says there are options to change springs though, so I'm quite unsure about that. While the flutter sounds nice, I do prefer it to be more beneficial than doing the opposite of what its supposed to.

I like the sound of the Tials.. well some of them.. Been looking for sound clips and it sounds nice on some cars but otherwise 'unspecial' on others.

How'd you get one sounding like this. (am a bit new to this.. please enlighten me)

Else: would you have any recommendations? (Have never really thought too highly on GFB but I see a lot of recommendations)

edit: argh.. been using too many curly braces... {}

[Pappu1]

yea thats the kind of "genuine" tial units that flutter a heck of a lot (not a fan of killing my turbo hence stay away from them personally)

but in all the time i have known, i have never had any flutter or leak issues with either GFB or Turbosmart thats for sure

GFB would defenately be the choice if i was putting a bov on mine as they are well designed in australia so at least getting quality products etc

[Swindog]

I only get flutter on my tial in low boost situations. If you have a tial and getting flutter you need to lower your spring pressure inside it.

[Pappu1]

 Swindog said:

I only get flutter on my tial in low boost situations. If you have a tial and getting flutter you need to lower your spring pressure inside it.

isint the idea not to have flutter in the first place - which is the main reason for a bov to exist anyway.. ay man

the tials are good for high boost as never seen them flutter on high but utterlly flutter happy on street driving hence wudnt recomend it (unless u do high boostor track work all the time then yea go for it)

thats what i wud say after hearing lots of different bovs etc.. the tials just not suited to a street suby

[dubbedup]

tried heaps of different bov's over the years all had some kind off flutter...usually under low boost...

i thouhgt it was ok...it wasnt comp surge ???

[Swindog]

Ive have been told a minimal amount is ok under low boost, but remembering ive built mine for track/drag uses, not that i get to drive it anymore but ive had it checked and its not surge, its the actual bov fluttering. We had a camera under there checking it.

I sent the video to Tial in the states trying to diagnose it itnitally and they said its the spring tension as it has a7psi spring instead of the 9psi spring. On the 9psi i do get surge. Its just the setup. You can modify the tial spring to suit 5psi but as its diagphram i wouldnt.

I had thought about stepping away from the tial to the synapse but at that stage id just spent $300 on it and welded the flange on. Plus the synapse was like $500 then.

[Pappu1]

 dubbedup said:

tried heaps of different bov's over the years all had some kind off flutter...usually under low boost...

i thouhgt it was ok...it wasnt comp surge ???

have heard few GFB and Turbosmart ones on mine and other mates cars and they never had any surge/flutter at all (properly set of course)

also the hks ssq (copy ones) seemed to eager to open and never quiet had any surge on them too

[dubbedup]

brand new GFB Bov, setup by 2 different dyno tuners and still does it...im not worried...just seems a fmic vs tmic discussion

[smokn4]

yea my GFB BOV flutters (under low boost only) and on high boost is all goods, i thought they was meant to be like that ???,

im running a GFB stealth-fx 100% to atmos

[gtlegacy]

http://en.wikipedia.org/wiki/Blow_off_valve

read this it explains everything

[Guest crunchy]

i rather run without one which can be done easily and give alot better result than a blow valve, i shouldnt have said easily so freely never the less it works well

theres abit to the setup but its different and looks dam cool

and just to upset people that make blow valves, ive made my first one over 20years ago and even now they cant make one that actually works correctly nor understand how to size them!!

for the record a blow valve size has absolutly nothing whats so ever to do with the power your making

i see all to often how "this valve will support 500hp" whatever.

if you remove the blow valve youll still make 500hp.

the trick is to know how much cfm to relieve without dropping too much boost or empting the pipes to induce lag or surge.

if your in the hunt for a show off valve, when you go into the shop ask them whats the cfm rating!!

itll be a silent reply

[nickch]

well.. CFM is the rate at which air moves, but doesn't that correlate directly with the amount of pressure you're running (not also ignoring length of pipe between turbo and intake (incl volume of IC))?

dropping too much boost doesn't seem too much of a possibility as the turbo will be spinning and theres nothing to actually force more air out of your intake other than then pressure from the turbo itself..

in that sense, i think with a lot of BOV models, its having to tweak it to be able to release enough air at maximum boost.. and i think a bit of flutter at lower boost is unavoidable, which seems logical as you'd need it to be stiff enough to not leak but still be able to release properly at high boost without fluttering..

at the end of it, i'd rather it be fluttering at lower boost conditions and have it perform optimally at higher boost.

this is just what i gather, do correct me if i'm wrong?

[Guest crunchy]

boost presure does not correlate to cfm sorry

turbo a" produces 500cfm@15psi turbo b" produces 1000cfm@15psi thus pressure doesnt mean much

piping length and cooler size has no part of it apart from the fact they act as an acumulator,they relate more as part of a pressure drop.

you can drop too much with an oversize blow valve thus inducing lag, that and too larger intercooler piping and not just length.

2" cooler piping will let you make over 500hp,so why do you need 3" piping on a 250kw wheel car when it should be on a 1000hp setup.

a blow valve releasing 300cfm and a turbo that can only produce 350cfm isnt a smart idea sorry,you empty the piping.

the spring in any blow valve is a neutraliser to overcome vacum volume, not all cars are the same

the trick is to have a spring that over comes this and also matches the piston area,eg the larger the piston the greater the spring area.( same as a wastegate)

the boost presure acting on both sides of the valve means the spring is along for the ride till the balance is upset as in vacuum applied to one side and boost spikes due to rapid throttle closure.

as for a little surge down low you are correct it does no harm,but in saying that isnt it interesting when a stock valve is removed and now you have surge with a so called bigger valve?

whats wrong with that picture?

aftermarket valves leaking at idle is more than just the spring, if you have to excessively wind the spring in to seal at idle then the spring doesnt match both the valve area or the vacuum of the engine or the hose doesnt match the piston area thus it cant deal with the volume.

so no offence but your not quit right.

opps i forgot to meantion but when the throttle is closed presure can build as high as 40psi for a split second when running as low as 10psi and thats when surge kicks in as the turbine is still being driven,but the compressor pressure is greater than the turbine which then tries to spin the comp wheel backwards.

apart from surge the thrust loading can be as high as 100 plus pounds on the bearing along with twisting the shaft causing breakage

[Pappu1]

 crunchy said:

aftermarket valves leaking at idle is more than just the spring, if you have to excessively wind the spring in to seal at idle then the spring doesnt match both the valve area or the vacuum of the engine or the hose doesnt match the piston area thus it cant deal with the volume.

soo how to deal with this situation where the bov will not seal under idle.. have a mate who has his bov opening up at idle and causing all sorts of idle issues..

i wud assume adding more spring tension wud be the answer?

(adding some packing under the spring so its more pre-loaded so can exert more force thus sealing under idle - does a semi compressed spring have more force than a fully extended one?)

[Swindog]

Crunchy... have you got yours on the shelves yet? Be keen to see if it cures the slight surge i have so i dont destroy one of your turbos.

Pappu..yeah you need a bigger spring. But again what crunchy said you need to weigh up what effect this has once the system is loaded.

Have to remember, BOVs do not suit all applications, it fully depends on the setup. If i could go back to a factory one i would.