I have asked this before, but how is it with open blow-off valves? Like, I have heard because of the mechanical AFM, the car doesn't like open blow-offs, but there is also something with single or dual pistoned valves, and so on.

Anyone know anything about this?

 

With the AFM, a BOV that vents to atmosphere is not really a great idea, because the ECU has already calculated how much air should be going into the engine, so when the BOV vents, it's not getting the air it thinks it is, and goes really rich. The way that this is overcome is to recirculate the BOV so it vents in back into the air stream at the turbo inlet duct.

I have no idea what single vs dual pistoned valves have anything to do with this, unless I completely missed the mark as to what you are talking about.

Also, a quick search could have told you all this.

 

I have ran an open Turbo XS RFL blow off for over 10k miles now without issue on stock ecu. It may make it rich between shifts, but nothing you will notice.

 

You get FIRE out the exhaust between shifts and revs with an open bov... which I love. Yeah the AFM goes rich for a second and if the exhaust is hot enough it ignites the fuel and shoots a flame... want videos? Doesn't bother me any. I run an old school HKS RS BOV (cause they just don't make them like they used to, huge, high flow and reliable), It doesn't "chirp" "tweet", "whistle" or make any other bird sounds or anything else like say an STI, just "woosh" and the psi is 0 within a second, like a bov should be.

 

I dont have mine recirculated either and no issues. Mine really doesnt shoot out a flame that often but when it decides to it deffinatley keeps people from tailgating

 

I ran an open BOV (Greddy Type S, oldschool) on Stock ECU and Rtek 1.7. It backfired and shot flames all the time.

 

open bov's with a MAF are not a problem at all, car runs slightly richer between shifts. no harm done.

 

So no problem except making Al Gore angry?`Well, the open ones are like 20$ cheaper here in Norway, ++.

I had a HKS SSQV on my Passat, open. The noise was so loud (I took out the part of the valve which made the noise really high), so I got a friend to make a resirc nipple instead. Just the same amount of noise, so didn't help, but the car became more responsive. Of course, a 97 Passat dont use mechanical AFMs, but rather proper electronical MAFs.

The point was the Passat was not recommended to run open with either, but it worked fine, except the little delay I got between gears because of the lost air.

 

But that's not quite fine. A BOV is supposed to relieve pressure in the intake tract to prevent surge and also allow the turbo to continue to pump air into somewhere, theoretically minimizing any lag between shifts. If the AF mixture was screwed up enough to cause a delay between shifts, then that sounds broken.

On the other side, the RX-7 ECU runs so rich by default that it really isn't a big deal. And most FCs are running so poorly at this point on the stock ECU that any lag caused by an open vented BOV is probably not noticeable due to the bad TPS, clogged injectors, etc.

The long and short of it is that open venting a BOV works fine on the FC.

 

If you use an open valve the air that the turbo got in is pushed out again, and it got to suck new air in. But with a recirc the air is just vented into the turbo again, so you get a little bit more air straight after the gearshift. It is barely noticable, but it is there.

 

On this same topic, if I were to purchase a greddy type rs bov, and recirc it, would I still hear it?

 

You can hear the stock BOV. So yes.

 

People that mention that crap are normally smart asses who want to make a point. I remember my Super Street teacher said some BS like "on cars with vane AFMs the engine will stall after a shift with an atmospheric dump BOV" lol...

In reality you probably won't even be able to notice a difference. I'm with arghx and others on this subject, and believe BOV's are a complete waste of money. No BOV ftw.

 

^ im sure this is a dumb question... but how do you safely run a turbo with no BOV?

 

I think he means no aftermarket BOV's. Ones that vent to atmoshpere.

 

disconnect it and plug the holes. If you still have the stock AFM you may not like the way it drives after that, but I can't say I've done it personally.

I haven't had a functioning blowoff valve in years: https://www.rx7club.com/single-turbo-rx-7s-23/8-months-counting-no-blowoff-valve-884695/ but I have a standalone. I didn't really notice any difference besides the fluttering sound. Turbo hasn't blown up (it is an aftermarket Garrett).