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