BOV - recirculate or not?
 

So the Greddy kit comes with a recirculating valve - is that the best/most efficient setup or would a Blow off valve provide positive effects to the turbo system over the stock recirculating type?
-Ryan

The Greddy kit doesn't come with a bypass valve, recirculating or vent-to-atmosphere (VTA). That being said, you'll want a bypass valve of some sort, as it'll help spool up between shifts and on/off/on throttle transitions.

The Miata uses a metered air setup, so for a problem-free setup, you'll want a recirculating bypass, but if you just can't do without the silly sound of a VTA bypass, there are ones you can purchase that don't leak at idle. This will prevent your car from stalling, but it'll still run rich in throttle transitions and upshifts, which may or may not cause some stumbling or less-than-crisp throttle feel.

Does installing any of these bypass valves require significant modification or can you just tap a hole in a pipe and screw it in?
Everybody talks a lot about the loud bov units but what is a good recirculating bypass valve?
-Ryan

Short answer, yes.

However, the design of the valves will differ, so mounting options will vary accordingly.

For a nice, clean install, you're going to want to weld a flange on the pipe so the lower portion of the valve is not inserted into the actual pipe (obstructing airflow).

This won't make that much sense until you see the different styles, and realize the advantages/disadvantages of each.

try to find a pic..


As far as other modification, you will need a boost/vaccum source.

Boost/vac source as in just a tube from the engine's vacuum system or something else?
-Ryan

Has flange on bottom. Will bolt to the flange to be welded on your I/C pipe.

http://i39.photobucket.com/albums/e1...ng/BOVSide.jpg


See how this one inserts into the pipe. No good. EDIT: See posts below for clarification, this valve can be used correctly.

http://i1.ebayimg.com/04/i/07/21/63/96_1_b.JPG

Right. From the intake manifold.

Must also say I don't have experience with the Greddy kit, and modifying it, so perhaps a more experienced user can recommend a specific BOV.

I would look at the sticky: https://www.miataturbo.net/forums/showthread.php?t=34 for actual examples.

Good luck.

By 'metered air setup' I'm assuming that is referring to the MAF? So if you were to use a non-recirculating bypass valve, as you upshift or off-throttle quickly, the MAF will sense less air suddenly but still dump the same amount of fuel as it was thus causing you to run rich for that short period of time? Or does it work differently?

And if you were to use a recirculating bypass valve, how much noise does it produce? I know blow off valves can be pretty loud. Does the recirculating type eliminate all noise during shifting and throttle lifting or is it just dulled down? Could be an issue if I choose to really try to keep the turbo setup as non-detectable as possible...

-Ryan

I noticed that when I got my vent to atmosphere BOV working correctly (don't ask), I don't hear my wastegate chattering anymore.

It also runs piggy rich, which is OK because my cat and my O2 sensor are already dead. Just waiting on the 2.5" Tony pipe and exhaust to come in to replace all that garbage.

To answre some more questions:

1) The recirculating bypass valve shown here: http://i1.ebayimg.com/04/i/07/21/63/96_1_b.JPG , absolutely does not stick into the path of the intake pipe. With this one, you would weld/JB weld a bung over a hole in the intake pipe and connect this bypass valve using some silicone or rubber hose and clamps, like this: http://www.bellengineering.net/Image..._front_1LG.jpg , http://www.bellengineering.net/Image...Install_Lg.jpg and http://www.bellengineering.net/Image...kit_front3.JPG

2) That particular Bosch bypass valve is used on everything from Porsches to Audis to Saabs to VWs. It works, and it's inexpensive (~$40-60).

3) ThePass, you are correct in your assumptions about the metered air setup ('90-'93 cars had an AFM, while the '94+ cars have hotwire MAF sensors to do roughly the same thing).

4) The noise/volume of the bypass valve depends a lot on placement; that is to say, if it's mounted over on the driver's side, toward the top of the engine bay, it'll be louder than if it's mounted lower and on the pass' side. My recirculating valve is cast into the compressor housing of the turbo so it's quite loud...almost sounds like a VTA bypass valve at full throttle shifts. I was going to build a more complete cold-air box to suppress some of the noise, but I've gotten used to it (and the stares it induces from the ricers in my town :) ).

The AFM / MAF will actually sense *more* air during the bypass period- not only the air that's actually getting into the engine, but also the air that's being dumped overboard. And it will call for the appropriate amount of extra fuel.

With a recirculating bypass valve, you plumb the output back into the system between the AFM and the compressor intake. That way, the air gets measured once as it enters the system, the bypassed air loops back around into the compressor again, and the volume of air flowing through the AFM is equal to the volume of air actually being consumed by the engine.

Yes, I guess it's a matter of semantics...well, not really, I guess your wording is most correct. The AFM has already measured the air, when it gets dumped overboard, the ECU has already accounted for that air and added the appropriate fuel, causing the rich situation.

awesome replies in this thread.

recirculation valves can also get the turbo spooled a little better between shifts. vta valves can cause a bit of unwanted attention. i am planning to use a recirculating valve despite not having a MAF/AFM. i just don't want to draw that much attention, make that much noise, or worry about the vta potentially leaking. sound wise, the cecirculation valves are noticable in the car, somewhat, but as corky bell describes it as more of a "sigh". the vta can sound anywhere from a "pshhh!" (like opening a 2ltr bottle of soda, but longer and louder) to a high-pitched whistle "eeshhh!". depends on the model and such.

the vta is more vogue, the recirculating takes a little more tubing/plumbing, but is cheaper and arguably more reliable and subtle.

You sir are correct. Thanks for the pic. Just trying to steer the original poster away from the wrong style valve. (Based on his mounting question).

ThePass: "can you just tap a hole in a pipe and screw it in?"

I've seen pic of somebody that drilled a hole in the pipe and stuck the valve (in link) in there. That's what I was thinking of anyway.

Thanks for all the replies! I just looked at the pics that Bripab007 posted and now I understand what that smaller dia. pipe is doing there that crosses back between the pipe near the MAF and the pipe at the throttle body... So really, a VTA bov would be alot easier to mount - you just drill a hole and mount it in the pipe. A recirculating bypass valve needs that whole pipe plumbed into the piping before the TB and before the MAF and then have the valve installed inline with that pipe...
Seems like if the kit didn't come originally intended to have that recirc. valve its alot of work to get one installed on it... correct me if I'm wrong.
-Ryan

Also, two of the 3 pics show the valve mounted near the throttle body - but one of the pics:
http://www.bellengineering.net/Image...kit_front3.JPG
Has the valve mounted on the drivers side of the engine bay at the end of the recirculation pipe nearest to the MAF - so there is nothing keeping air from going into the pipe near the throttle body. This seems like it would be terrible for airflow since air would travel up that pipe and as it almost gets to the throttle body, there is a whole seperate pipe that will get filled by air - with nothing keeping it from getting into that recirculation pipe because the block - the bypass valve, is on the far side of the pipe.

Seems awfully bad for airflow to me... any one else think so or do I not understand things correctly?
-Ryan

DOG -
Are you implying that running VTA makes your car run "PIGGY RICH"?
I've never heard of this, but I would be interested if others have this symtom from running VTA..........

LOLA

I would imagine that running rich during that breif period, while maybe not doing anything better for the engine, certaintly isn't bad for it. But I wonder about the throttle response...
-Ryan

Dude, tons of people have shown the running VTA bypass can (not always, but can) causes drivability problems.

What kind of driveability probelms specifically? Idle problems I would expect if using a low quality bov that leaks at idle... but what else are you referring to? I'm curious as I would prefer to use a VTA bov for the simplicity but don't want to do it if it means a loss in performance or bad driving characteristics.

-Ryan

Filling up that tiny pipe with boosted air shouldn't lead to any measurable decrease in throttle response or performance. I'd not worry about it, especially since Corky Bell designed it.

Secondly, you don't need to fashion a hard pipe like that, nor do you need to mount the bypass valve so far from the throttle body if you don't want to. This pics show roughly the same procedure and pieces I used to mount the Bosch bypass valve to my parents' Greddy kit, only, unlike these pics, I mounted the bypass in the correct direction (reverse of how it's shown here): http://www.15psi.com/BOV.htm

It was like ~$65 in parts and ~30min. of my time to install.

Ya = I've noticed that the car wants to turn left and right more often with it. Real loose front end, like my tie rods have fallen off!

Eh?:eek: :eek5:

I have a Forge VTA BOV, it's a diaphragm type BOV. It leaks at idle and makes it sound all lumpy, it's one with a filter around the vent. With a VTA and an open element air filter, you'll still get a little whispering of the BOV, it just won't be that obnoxiously loud PSH! sound. Kind of like you you can hear the turbo spool up, you'll hear the BOV in a recirc.

It'd be interesting to see just how lean you're running at idle and cruising conditions when that VTA bypass valve is sucking in un-metered air.

So that www.15psi.com website - is the recirculating BOV on there a good unit and is that a good kit or is that just somebody who doesn't know too much making shoddy stuff in their garage? It looks ok...
-Ryan

Yes, the kit of 15PSI's website is incredibly easy to replicate yourself, for a bit less money (maybe $60-70 total, or less if you already have a drill press with large bit, etc.). There's nothing particularly shoddy about it, though; don't try to overcomplicate what a bypass valve is, be it recirculating or otherwise: it's just a very simple valve to divert air through some tubes.

That particular Bosch bypass valve has been used for years on Porsches, Saabs, VWs, Audis, etc. There's nothing sketchy about it.

It will make the engine run rich, during the brief period when the valve is open, if and only if you are using an AFM or MAF sensor which directly measures the volume of air entering the system.

Those engines which use MAP as their primary fuel metering sensor will not suffer this problem, since they have no concept of how much air is being drawn through the intake- only how much of it is actually getting into the manifold.

Flying Miata sells this blow off valve on their website:
http://www.flyinmiata.com/index.php?...umber=05-90110
It's from GFB and it is a VTA unit - but they specifically say that it has a special piston ring that makes a perfect seal and: "this means the valve can be used on a car that uses a MAF or AFM to measure airflow"

Are they just referring to the fact that it seals perfectly so it doesn't leak at idle, or are they somehow saying that this unit will work for a MAF metered car somehow? They sell a different bypass valve that is a recirculation unit, so it doesn't look like this bov can be used as a recirculation type...

-Ryan

Well, I don't have a wideband yet so I couldn't tell you. It runs pretty good at cruising conditions, but it idles like a retarded monkey with Parkinson's. ALMOST stalls every time, I'm pretty good at heel-toe so I just use that at stop lights.

So, why are you using that VTA bypass on your car since it's causing such significant drivability problems?

Me? Because I'm stupid and didn't hear anyone whining about drivability issues. I'm looking for the Porsche turbo recirculation valve now. It's a brass piston type valve, pretty solid from what everyone says. I've found some aftermarket replacements for a relatively decent price (sub-$150) so I may actually go with that since they're aluminum instead of plastic. My cat needed replacing anyways, so running piggy rich isn't a big deal to me except sometimes my exhaust reeks of gasoline even after parking and I'm used to replacing my 02 sensor because I had a small head gasket leak last year.

I need to re-find those though, I'll post links when I do.

Here's the Bosch valve for $40: http://www.paragon-products.com/prod...110.337.50.htm

I think I bought mine for ~$50 shipped. I've said it before, and I'll say it again. If Porsche, Audi, VW, Saab, etc. saw fit to use these in OEM applications with warranty concerns and the like, I see no reason to believe that they'll break because they're plastic. When you've actually held it in your hand, you quickly realize it's not a fragile piece of plastic.

BEGi also sells a nearly identical one, although I'm not sure if it's Bosch or what: http://www.bellengineering.net/Pages...ata_parts.html

Firedog: Temp solution = http://www.jgstools.com/turbo/oav.html

Easy way to Reirc.:

http://www.magnaflowonline.com/image...d/elbow001.jpg

tools needed:
jb weld
drill - tap and bits
threaded pipe

My bov is recirc. and is still fairly loud

What size of bit, tap and pipe nipple did you use to do this?

actually, it was a 1" pipe, and I used a 1" hole saw. That's it, screwed in tight and JB welded it. The hardest part was sourcing the heater hose to fit. It's 1.25" OD. Matched the opening of my bov.

You don't have to be incredibly precise with it; just make sure the diameter of the pipe is roughly 1", to equal the diameter of the inlet/outlet of the bypass valve.

You don't even really need to drill/tap the bung. You could just use an unthreaded, ~1-1.5" long section of ~1" diameter pipe, shove it into a hole you've drilled that's ever so slightly larger than 1", and JB weld, MIG/TIG weld, etc. I had my buddy TIG weld the one I did on my parents' car, but it could've easily been just JB welded.

Edit: Braineack beat me to it! Don't make it difficult, just do it!

Thanks guys!

Jay

See also...

http://www.stratmosphere.com/hyperboost.htm

Aluminum.

So this bov attachment:
http://www.jgstools.com/turbo/oav.html
Is basically an add on to an existing recirculating bypass valve? It looks like it comes with a hose and clamps so you can attach it to the other end of the Bosch valve so that it vents to the atmosphere?
Really, is the only problem with the VTA that it leaks and causes rough idles, stalling, and lean conditions while crusing? Because if so, this seems to be a nice peice from that will not leak and not cause those problems... you could get the Bosch and this attachment for ~$65 - alot less than any high quality VTA that won't leak...
-Ryan

A lot of members here, and myself (have), use one way check valves on the end of the bov to keep it closed on idle. This is the same premise, but designed for a bov, not water.

Is it necessary to use something like that to prevent leaking at idle with any bov or does the Bosch unit not have any leaking problems?
-Ryan

The Bosch unit leaks at idle, but, because it recirculates, it's not a matter of any concern.

My Turbo XS Type S doesn't leak at idle

Not a matter of any concern as in, because it recirculates it doesn't cause idle problems? Does the leaking cause any performance losses? It seems like if its leaking it can't be good...

-Ryan

Not a cause for concern because it recirculates, so, yes, no idle problems. When you're under boost, it's held shut by the pressure on the signal line. While you're idling or in partial vacuum or light boost, it can leak a little bit, which is fine. That's what it's meant to do.

Edit for spelling.

This has to be the longest thread about BOV ever... thats even comapring it to M.net. You girly men!

I think I'll add more riviting multimedia to the discussion. I made two quick videos of my recirculating bov as heard while driving with the top up.

http://www.rev2red.com/images/cars/CIMG0108.AVI

http://www.rev2red.com/images/cars/CIMG0109.AVI

Sounds about as loud as my VTA with filter, not very loud at all, just enough to hear if you're listening.

It's noticeable but not as apparently loud like some other bov's. It cant be heard from the street as well as other cars on the road. But it is significantly quieter than when I ran it vta.

Im hoping roman posts what his FM, VTA sounds like.. Its loud..

When recirculating, the Bosch doesn't leak, it is held open by Vac, allowing the air to recirculate. and as Brian has mentioned absence of Vac closes it.

One of my Subaru owning neighbors has one of those short ram air filter systems on his WRX STi. It's pretty loud, I heard him coming down the street with it. My BOV is VTA, but it has a dust filter around it, it just whispers when it lets off.

Try running a bigger vacuum line to it.

My recirculating bypass is cast into the compressor housing, and it's fairly loud when just driving around town at part throttle. Between shifts, though, it's about like Braineack's.

ThePass

If you read the text a little closer on the link that you supplied you will see that it says
"The piston is actually fitted with a piston ring for a perfect seal. Combined with a well-chosen spring, this means the valve can be used on a car that uses a MAF or AFM to measure airflow."
The most important part of that statement is "with a well chosen spring", a perfect seal can be detrimental in a VTA BOV on a MAF car if the spring rate isn't correct. There are piston type valves on the market that work because the tollerances are so loose that the vacuum will not lift the piston at idle. If the valve is designed with an airtight seal, such as ours and the GFB that you listed, the spring tension needs to be chosen for the application. That being said, I never recommend a VTA valve on a MAF car. Which leads me to the following...

firedog25

Do you know the color of the spring in your valve? I can send you the next stiffer spring to see if that cures the problem. Or we can go another route and get you the right valve for your application. If you prefer to have VTA you would need to use our 004:
http://www.forgemotorsport.com/conte...roduct=FMDV004
Or if you wish to recirculate go with the 007:
http://www.forgemotorsport.com/conte...oduct=FMCL007P
Just ship us the 003 and I will send you your choice of these two valves with no additional charge.

Pat

When they say it can be used with a MAF/AFM car because of the well-chosen spring and seal, they just mean it won't leak at idle. If it's a vent-to-atmosphere, it'll always run rich between shifts in addition to possibly leaking at idle, unless that well chosen spring happens to be on so stiff it renders the piston useless...at which point you no longer have a functioning bypass valve :)

Well I figured I might as well contribute my experience w/ VTA and recircs as well as the BOV of choice for me.

First of all let me say I ran a eclipse GSX @ 17 psi running several different BOVs. First I had a turbo XS RFL (really ...loud). I blew off about 5 feet from some lady and she banged her head on her roof cause it made her jump (she was bent over gettin something out of the seat). As great as that moment of my life was, the rest sucked. My car ran rich and dumped fuel between shifts and also had a very crappy idle due to the MAF trying to compensate for the air.

Next I tried the 1g DSM metal BOV. Let me tell you, if your looking for a SOLID (17-20psi uncrushed) bov.. this is it. Its SUPER quiet and you can get it ALREADY flanged onto the 1g DSM pipe section for roughly 40 shipped off dsmtuners. com.

I however, upgraded my pipes and transitioned to the Greddy Type-S (no longer made I guess). This BOV held boost awesome and possessed I would describe as a "middle" loudness sound. It sounded like a "Ka-Chink" between shifts. I ran it at 14 PSI and it held fast. If I could find one again I DEFINITELY will use this on my turbo miata.

Hope this helps w/ your selection.

It's what I'm using suckers.

Really? COOL. Could you e-mail me information about this at firedog25@iafflocalf-53.org? Thank you.