Blow off valve?

I didn't know any factory turbo cars in the U.S. came with blow off valves? I'll be damned if I am wrong though.

Last I knew, it was an air bypass valve.

I've driven the U.S. spec Evo and didn't hear any chrips when I changed gears so this one is above me saying they come with blow off valves.

 

Sorry if this confused you, termonology can be a funny thing, there is the so called "officially correct term" and then there is the most commonly used.
If I were to have used the OEM term "air bypass valve", I believe this would have created more confusion. All of the aftermarket manufacturers (Greddy, HKS,etc) use the term blow off valve. In fact do a general search on the internet for "blow off valve" and see what comes up.
I believe what you indirectly tried to describ as a blow off valve is now more commonly referred to as a pop off valve.
http://cvm.msu.edu/services/aneth/docs/popoff.htm

So these days an air bypass valve is commonly referred to as a blow off valve. They can be more specifically identified as REC BOV(recirculating) or VTA BOV (vent to atmosphere). IMO using the termonology that is most widely understood by your primary audience is preferred. A rose by any other name....

 

I totally understand. But for any of us to dub the air bypass valve as a blow off valve would be not only absurd, but a contradiction in terms.

By virtue of operation, an air bypass valve does not 'blow off'. It's not a sliding piston. And it doesn't exrete any gas into the atmosphere. How can one circulate what he/she is blowing off? It is contradictory.

However, there are some odd hybrids that do both recirculating and atmospheric venting simultaneously. Paradoxically, those types are both ABV's and BOV's. But that is not in stock form.

 

Your bringing a stick to a gun fight... "even if your right, your wrong" if you know what I mean. You don't wander into a forum and cross swords with one of the most respected members over symantics... It's like walking into a Texas Cowboy Bar, and trying to tell a bartender in front of everyone that y'all a'nt a word.

 

The function of the BOV/Air Bypass Valve is to vent (or one could say "blow off") the excess turbo pressure when the throttle plate closes.
So your saying that if we disconnect the intake return hose and let it vent directly to the atmosphere, then it's ok to call it a BOV? Then by simply venting the air into the intake, all of a sudden it becomes an absurd contradiction in terms?
If it makes you feel any better, the intake is ultimately connected to the atmosphere, and I am sure some of the vented air gets pushed back out of the intake into the atmosphere. Hence the highly audible air release noise when the valve is activated, even when the valve is configured to re-circulate.

What are you talking about? It is a sliding piston, a sliding piston that is actuated by the intake manifold pressure.

How about this; the valve is blowing off excess pressure in the intake tube going from the turbo to the throttle body. This is accomplished by venting/re-circulating the air back into the intake.

Bottom line, whether the name BOV accurately describes it's function or not is really unimportant. The fact is that this is the most commonly used term for this device in the aftermarket industry. Even aftermarket valves that are clearly designed to vent back into the intake (or re-circulate), are dubbed BOV’s by the aftermarket manufacturers.
I did not come up with this name, but I do not think that it is necessarily absurd or completely contradictory either. I still believe that it is best to use terminology that will be most widely understood by your core audience. For that reason alone I will continue to refer to it as a BOV, in all it's various forms and configurations.
Perhaps the term air bypass valve was to generic for the aftermarket companies? Not to mention the term blow off valve just sounds cooler .

Kind regards,

Eric

 

I'm with Eric. Nuff said.

 

Oh yeah, a final word on the PSSSSHHHH we all want. Due to our Evo turbos and how the BOV work on them (recirc vs vta) we really don't get as satisfying a sound as someone who vents to air. Now it can be improved based on the type of air intake upgrades you do, but it still isn't as good as I'd like. And if you have a good audio set up, you'll probably never hear it. Oh well, I prefer go over show.

 

 

Eric,

I just returned from my trip and I tested the Greddy valve using a hand vacuum pump. The valve did begin to open before 16 in/hg but it would not hold. The vacuum pressure immediately begins dropping slowly until the valve closes.

How long should it be able to hold the vacuum before you would characterise the valve seal as faulty?

Thanks,

 

John,

That's your problem, the piston actuator chamber should hold vacum/boost indefiniately. I let one sit on bench under vacum all day, it was still at the same value when I came back.
A leaky actuator chamber will also cause the valve to leak boost under WOT conditions. If you can, putting pressure in the chamber might make it easier to find where it is leaking. Hopefully it is a fitting or something simple and not the rubber piston seal. I am not sure if greddy sells just that part.
I also put a little grease on everything internal, that will help keep the rubber from binding/pinching also.

Good luck with it, let us know what you find.

Regards,

Eric

 

Eric,

Pulled the valve apart and resealed all fittings with teflon tape a second time and still had leak coming from the adjustment screw. I then tried some PTFE thread sealant and still no luck. I finally decided to preadjust it for the minimum amount of tension required for the screw to seat in the spring platform and seal it with RTV silicon sealant beneath the washer and locking nut. That did the trick. Now it begins opening at @ 12 in/hg and holds the vacuum as it was designed to.

Idle instability problems are gone, no part throttle hesitation issues, and this valve holds higher boost pressure than my stock DV, which must have had a flaw in the seating surface. Bottom line is that the Greddy Type-S performs as you indicated it should. Thanks for the help.

Regards,

 

any whistling at idle or vacuum part throttle??

 

None.

 

Hm, is there a kit I need to buy to get the GReddy TypeS to work with the Evo? Like, if I bought the unit used or something?

 

So basically in the end in order to
1) Get a better BOV than stock to prevent leaking at high boosts
2) Get recirc for evo's
3) Have a little bit of cool psssssssssh sound than stock

You are left with the two recommendations which are:
1) Greddy TypeS with one spring mod
2) Forge DV recirc
3) possibly the GoFastBits hybrid VTA/recirc

Is this a correct summary of the board?
btw by getting a recirc BOV like the TypeS or Forge how much of that pssshhh sound are you really going to get, noticable enough for the driver with windows down or something? Becuase essentially the boost leak is minimal so I would get a BOV juss for the improved sound

PS, forgive my ignorance but about how much psi does a stock evo turbo put out?