CantGoStraight

Actually the screw your tightening up increases the spring pressure against the piston that the vacuum pulls against, it doesn't close up the oriface it just requies more vacuum to open it and closes the port quicker as the spring pressure over comes the vacuum, this is what gives you a sharper (louderblast of air) screw turned in as opposed to a softer longer discharge (screw out) aftermarket BOV manufacturers have other gimmicks such as heavier springs and port inserts to achieve the sound and boost pressure needs of the buyer.

Narfle

iTrader: (16)

I see. This is good to know.

MrRx

iTrader: (1)

stock BOV > aftermarket

unless you want the whole "ricer" sound :p

Narfle

iTrader: (16)

I have heard the for high boost applications(over 15psi) the stock BOV become a liability. But on stock turbos....yeah theres not a great reason to do it other than the sound.

dgeesaman

iTrader: (7)

The compressors never spin in reverse, or even close to zero. The airflow always flows into the engine, and the exhaust always flows out. Sometimes the compressors are driving the air, sometimes they are dragging on it, but they always flow in the same direction.

I'm afraid I don't have facts to add about how BOV settings affect compressor surge, and how this *might* cause the turbos extra stress. However, if the turbo is rubbing on the housing to make the noise, they need replaced. Simple as that.

Dave

Narfle

iTrader: (16)

I was initally out of line in this thread and I sincerely apologise to streetRX7. He did not deserve my toungue lashing.

Narfle

iTrader: (16)

Im going to disagree. In a closed BOV, closed throttle, high boost situation the exhaust pressure on the turbos would be less than the pressure exerted by the compressed air in front of the turbos creating this bounce that I spoke of. I know LITTLE about turbochargers. But it seems to me that even in some remote circumstance it would be possible to spin the turbos in reverse in a running engine condition. I mainly believe this because with the throttle closed to idle there would be lots of pressure in front at boost and relatively little pressure behind the turbos at idle. Wether or not this is possible simply depends on how much boost youre pushing and how much exhaust youre putting out. I think, the larger the turbo the more real this possiblity becomes.

Narfle

iTrader: (16)

backspin is a reality

The blow-off valve is essential to all turbocharged vehicles. The purpose of these Blitz dual drive blow-off valves is to relieve compressor surge without reducing compressor speed. They control boost pressure that is built up by the turbo and vent it into the atmosphere when the car is not under load (in between shifts).This prevents pressure from backing up into the compressor housing, causing the turbo impeller blade to rapidly stop or, even worse, to spin backwards (compressor surge or backspin). Doing so can be potentially destructive to the turbine wheel and shaft. Repeated stress over time can cause eminent damage to the turbo charger and eventually lead to turbo failure. The blow-off valves are actuated by pressure changes only, ensuring quick valve responses and complete closures at idle. Blitz's dual drive blow-off valves not only improve performance and response, but they also increase the life of the turbocharger.

from:http://store.summitracing.com/defaul...5&autoview=sku

dgeesaman

iTrader: (7)

Nobody said you were wrong. However, it's nice that you're participating in a more friendly manner.

In theory this is possible. In practice, I think you'd have to set the BOV to such a low vacuum that it wouldn't open at all, and not vent air for at least a second or two. (Remember, it takes about a second to spool the turbos, so stopping them would be similar).

I was reading about some of these aftermarket BOVs, and it's not clear to me how crazy (wrong) you have to adjust them to cause this problem. But it does appear it's possible. I suspect that bearing damage is more likely with a ball-bearing turbo, since high rpms will quickly kill a ball bearing. Sleeve bearings in can carry greater load at high rpm, but it's not clear to me whether heat becomes a problem instead.

I sure would make an effort to get that BOV properly adjusted. It's pretty sad when what amounts to a noisemaker may have killed your turbos.

Dave

dgeesaman

iTrader: (7)

I continued to research it and found similar info. When I was writing that statement, I was mistakenly picturing the stock setup. Aftermarket BOVs give you more adjustments that give you opportunity to F things up.

I think you're right - if you really have your BOV adjusted wrong, you have the elements necessary to create a bad compressor surge instead of vent it like it's designed. It seems like it would need to be a pretty extreme set of circumstances, but it's possible.

Dave

silverflash2

iTrader: (2)

Read this about eliminating BOV, a tuner specialist from Australia eliminated all his BOV on all the FD he works on, and explains it pretty well. Look under Rice Racing post

https://www.rx7club.com/3rd-generation-specific-1993-2002-16/about-eliminating-stock-bov-495277/

Rxmfn7

iTrader: (4)

Real mature. If you feel the need to post like this go talk to the kiddies in the lounge, this isnt the place for it. If you can't make a post without calling someone names and swearing, then dont post at all. You aren't helping anyone by doing so.

I dont really want to get into this whole discussion, but I really think you (not just you presonally, alot of people) need to do more research into the necessity of BOVs and what alot of racing teams have experimented with in the role they play with controlling compressor surge, or lack there-of. I think you will really be suprised in what you find.

RotorJoe

So does that mean compressor surge is not as prevalent as everybody states? and we have all been dooped into buying rice?

This is very interesting.

Narfle

iTrader: (16)

If its too tight you put undue stress on your turbos or possibly even bounce them back. If its too lose you lose boost response. Please send me to a place to learn. I yearn for the knowledge of this clubs senior members such as yourself. And Ive been researching this periodically all day. As I do not have an adjustable BOV Im not intensely concerned with these adjustments but may be in the future. But the basics seem very simple and fundamental to me. Its the methodical bleeding of air to best maintain boost and save your turbo at the same time. You find the line in the sand like any other tuning.

Youre absolutely sarcasticly right. I was a big jerk and Ive apologised here and privately to streetRX7. In explanation of my jackassery: I posted something correct. I was told I was wrong. I flipped out. I apologise again. I normally dont get so heated over nothing and in the end it turns out streetRX7 was just as right as I was I simply didnt understand what he was saying.

Narfle

iTrader: (16)

Prevalent in what sense? Every time you shift youre toying with compressor surge. If your BOV is closed youre going to stress your turbos...But at stock boost levels it may not be as large an issue as a T88 running 25psi. No one has been duped I hope. An Aftermarket BOV may not be necessary on stock turbos but it certainly wont hurt(unless its too tight). And anyone with a single or crazy twins would certainly be beyond the parameters of the stock piece. Its a matter of taste and necessity

RotorJoe

/\ Did you read the link silverflash2 posted?

From what I gathered in RiceRacings posts, you don't need one. Did I miss read something?

I get what he is saying about having to build up the boost pressure again due to the BOV venting it all but I thought compressor surge would kill you turbo if you didn't have one. I don't understand the parts where he explains why you won't need one.

Thanks
Joe

Narfle

iTrader: (16)

He may well be right but I dont buy a word of it. He talk about turbos before BOV's and how he "single handedly" proved that BOVs are bunk. Im gonna go research turbos pre BOV but the physics of the turbocharger say that you cant do that without stressing it out. maybe he uses super strong turbos? Ima go look into it but like I said I dont believe a word of it...yet

Rxmfn7

iTrader: (4)

Read this thread also:

https://www.rx7club.com/showthread.p...ght=blow+valve

Pretty good info and personal experiences there. Im not saying one isnt necessary at all or doesnt/cant serve a purpose, but I do think people place alot more concern than is needed on a BOV.

Narfle

iTrader: (16)

Theoretically speaking, If you drew your pressure reading from between the compressor and the throttle body your wastegate would prevent the turbo from receiving and extra charge from the exhaust gases in an off throttle situation. Thats what ive gathered so far.

So, now there nothing pushing the compressor which is still spinning like a demon. And the wastegate is open so no gas is pushing it from behind. So when that wheel keeps trying to push air into the same chamber thats already full its still going to bounce. That wheel still has a bunch of momentum and its still pushing air where it wont fit. The turbo is only more likely to backspin with no exhaust pressure on it. So yeah. The surge is gone. But the bounce is still an issue.

And, that wouldnt be an obvious problem because you dont take any data on your turbo's rpms so you wouldnt even know. These race cars he references that run 36psi up pikes peak with no BOV are race cars. Theyre rebuilt every race and the turbos are not run of the mill units I assure you. All they have to do is survive 15 minutes and theyre done and probably dont race again. The turbochargers before BOV's he talks about broke down more than we do. Early turbocharger technology sucked. Hence the advent of things like THE BOV!

This flutter that you hear in this situation. The one that is blames on the wastegate opening and closing and not the turbo fluttering. Well its half right. Every time the turbo pushes boost into the closed chamber over your desired level the wastegate opens and the turbo bounces off. The boost leaks. The wastegate closes. The turbo bounces the other way. The boost builds up with no where to go. repeat process.

The last two paragraphs are conjecture. Im not a race mechanic and I dont design Turbos. I am real good at physics though. And thats the only way I could understand it happening. When a turbo wheel with only momentum behind it strikes a wall of air it will compress the air and bounce off(think air ride suspension).

Im keeping my BOV and my HUMBLE suggestion is that you do too.

manny34711

ok guys yeah i tightened the screw almost all the way which means when it was letting the pressure out, it was so tight that it was not able to let all of it out. turbo prolly back spooled and bam. it had very little shaft play before. turbos have 100k on them so its just about that time. they were boosting perfectly before, about 12-14 psi but now im lucky if i get 5-7. Stupid me. So now im in the thinking process of either getting me a nice set of bnr twins, some 99 twins, a nice single (nothing crazy, maybe a 60-1) or just parking the 7 and getting me a lil beater hatch civic or something. what do you guys think.

dgeesaman

iTrader: (7)

A set of good used twins plus new gaskets is $600 and you can be done in a weekend. What's wrong with that?

Dave

manny34711

i want some bnr's man

Narfle

iTrader: (16)

BNR's are incredible! I always thought it would be really nice to have a beater to take the pressure off of my FD. I dont think you can go wrong either way. Follow your heart