BOV--Lack of--what harm in the short run
 

Does anyone run without a BOV? What harm will I experience in the short run running without one?

oh christ.. please mods lock this thread right now! its gonna turn into a huge disagreement like last time!

Read this thread, the 6 or so pages of it and im sure that you'll find an answer

https://www.rx7club.com/showthread.p...ight=point+bov

I sorta, almost, kinda read that one. I think I'll go with what WhiteFC says if he replies to this one. I think he has run without one before. I could be wrong. Let's say when I boost...I let off the throttle with some ease instead of letting all off at once? I will get one, bov, but not for several days.

why not just use the stock T2 BOV if your worried? should be easy to find one in the wrecker's...

I have to weld. glue, afix a nipple on the new fmic piping to do that. The Tuboii bov I chunked on the shelf for now. I'm thinking of soldering a nipple on the new pipe and reinstalling the old turboii bov. Just thinking of it. Ain't doing it ...yet.

If I solder a nipple on....do I have to drill a hole in the new duct? (late Saturday humor_)

I'm still getting over the initial shock of you starting a thread with a question...

.........

OK, I'm all better now...

With all the gauges and gadgets you have, and realizing you're the one in control of the throttle, I say go for it...

Then again, I don't run with those fuel-sucking maintenance nightmare engine destroying animals known as turbochargers, even though you keep telling me to get one :)

Maybe I'm just a little jealous because I don't have one......................Naaahhh

I consider the turboII cars trouble free compared to the non-turbo, gas sucking, aux port sticking, slow mobile n/a's. With the turbo car I can acutally merge in traffic and actualy accelerate in fifth gear. P.S. I have both types. Sometimes I actually drive the n/a and it's really a fun car.

Oh! Did I mention that Turbo cars don't hesitate???? humor

They don't, lol? You haven't been reading all of the threads started the last couple of days, then. Digi, for one, has got one going right now (hesitates/ surges at WOT, I think)...

One of these days I might actually get a turbo for a "fun" car, but it doesn't make much sense for my 100 mile a day daily driver :)

I don't have any problems merging into traffic- something must be wrong with yours. Need any help with it? :)

***I don't have any problems merging into traffic- something must be wrong with yours. Need any help with it? ***

YES! Tell me where a shop is within five minutes of my house, who can weld on a Greedy BOV for five bucks or less, including the BOV. And it wouldn't hurt if they came over and picked up the car and returned it in thirty minutes.

More humor? :)

You don't know anybody around you with a little TIG unit? What about RP in Dallas? You know, the little city directly to the east of you...

A BOV is really only necessary for a smaller type turbo like a stock rx7 turbo and other turbos on small displacement engines like imports. Some of the domestic turbo cars, take a grand national for example, came with a larger turbo. Same for deisels. No BOV on those vehicles. The reason is because compressor surge can harm a smaller turbo...it has less rotating intertia because it has less mass. IT is easier for surge to slow down or even reverse direction of these smaller turbos. THe bigger ones don't have to worry with it because theyre much stronger. Severe surge on a small turbo can actually break the shaft in half.

With that said, the main thing you'll have a problem with when running no BOV and stock fuel injection, is surge actually interferes with your AFM. IT can pass through the turbo compressor side and cause the flapper door or cone to slam shut which plays hell with your injection...it basically would cut fuel and cause the car to sputter momentarily. I have seen this happen on some cars before...and not on others.

IF you're easy with it Im sure there won't be any problems.

the reason diesels have no BOV is because they have no throttle plates!
Lots of cars don't have a BOV and last a long time.. my metro turbo has no BOV, some older porsche 911's don't either.

I wouldn't call stock TII turbos "small".. they're much bigger than turbos on DSM's/WRX/etc.

smartass;)

Let me rephrase that. Some vehicles have large turbos, such as those turbos that come on large displacement domestic engines or diesels. Those larger turbos can withstand surge without any problem.

Dare I say it again... ok.. you've made me do it..

You wont have any problems not running a BOV HAILERS, and yes when I was running my turbocharged N/A engine before I killed it, I didn't have a BOV, the turbo is still in factory showroom condition :)

and I really... REALLY don't want to start another shitfight here.. but...

"The reason is because compressor surge can harm a smaller turbo...it has less rotating intertia because it has less mass. "

Care to explain why requiring less force to turn it backward, which doesn't happen for some seconds mind you, would harm the turbo more?

Anywho, I've pretty much said my piece in that 'other' thread. :p:

I've been told my respected turbo builders that they've seen smaller import turbos broken as a result of surge. I tend to take their experience over anyone's word or speculation. I have not personally had any turbos tear up running with no BOV, but I have had cars where the surge interfered with the afm.

Ah I see, fair enough then, it's just i've heard that a turbo repair place said not running a BOV wouldn't help the turbo last any longer.
This was a T25 on a 2ltr motor. (ie, small)

Strange.. so many differing oppinions.

Well, I never had a problem.. (running either the stock AFM or later on my microtech)

I've been playing it safe and have only boosted to around five psi max. I can hear a tingle. tinkle sound when I let off. I thought it was a rattle in the dash at first. Acutually it sounds like detonation/ping more than anything else. But it's only when I let off the pedal, so I ASSuME it's not detonation.

It's a newly rebuilt, no shaft play at all turbo and I did not hear this tinkle prior to the new fmic.

I'll probably buy a BOV from that outfit in the suburbs of Ft Worth (Dallas/Garland) called RotaryPerformance.

Or maybe I'll weld on two nipples and use the factory BOV. One nipple for the BAC(WHICH I MISS VERY MUCH). While I have a good idle at 850, I find no bac means you have a lack of the ability to fine tune the idle without the bac. IMHO.

About the AFM door slamming shut: I have a problem with that idea. When you let off the throttle on a RX7, the fuel injectors go to zip/zero output. Shutoff. That's normal and a product of the tps/ECU. So I don't see how that could cause a problem. Shut the fuel pump off?????? Well the fuel rail maintains pressure for over twenty minutes when you turn the key to off is my answer for that. And if you have a bov, does it not open and let that pressure in the turbo outlet duct route back to the front of the turbo, where the afm is sitting? I think so.

On the other hand I might just leave it as is and go for broke (GO FOR BROKE, the motto of the 100th infantry battalion in WWII, or the one, puka, puka if you will. all nisei).

I can only convey my ideas and my experiences. Your ideas and experiences may not be the same. You asked the question, not me. :rolleyes:

Only at a ZERO throttle situation. What about, for instance, climbing a hill at medium throttle where you build 2-3psi and at the top you let out a little but not all teh way...where is that pressure going to go? You saying fuel should be cut then, too? So if that pressure did go out and interfere with the afm door, you're saying that fuel shutoff would be desireable and normal then?

I would say your answer is wrong. IF you've ever been in an s4 car with a fuel cut switch and flipped it off while driving under load (just for the hell of it) you know that the engine dies off before you can count to 1001. You cant seriously expect me to believe that this wont cause stumbling or hesitation at the very least. This is what I experienced in a couple of FMIC cars with stock EFI and no bov. Severe bucking was mainly noticeable when going from medium to light throttle, not so much from medium to none or heavy to none.

Hmm werid, I never had that problem with my old turbo setup with the AFM.

If anything, the stock BOV would more likely close the flap in the afm, not the car without a blowoff valve. Where do you think the pressure from the BOV (stock) goes anyway? I gotta put a pressure sensor in my intake duct someday....soon.

So I can sleep better....I bought a BOV from RotaryPerformance this am. One that vents to the atmosphere and gasses lillte old ladies who smoked too much in their youth.

So while I'm here.........I got to thinking about the stock bov and using it instead of making RP richer. So I thought too much about it. The stock bov only deals with the trapped pressure in that small intercooler and piping to the throttle body. So if you have a huge fmic, you have much more volume to deal with what with the extra piping and tripple size intercooler (over stock). That's why I went with a external (?) bov.

Hmmmm. I wonder if the tinkling I heard was the afm vane doing a tinking job. Open, shut, open, shut with surging pressure when I let off. I've got a way to find out. Just look at the output voltage of the afm on the SAFC or a meter.

Okay, if you know so much about everything, why even ask for other opinions, just to categorically shoot them down? :confused:

Oh God not again.....

IF you look at the last remark, you'll see I was giving your thoughts consideration. That tinkling sound I was hearing, that I'd never heard before, could be the vane in the afm slapping against its stop. The tinkle sound only happen when I gently boosted to three to five psi and it happen when I let off the throttle. And it wasn't detonation because it happen when I let off, not during acceleration.

If I knew so much about everything I wouldn't be posting so many questions. Your the touchy sensitive type, ehh? Cheeeez whizzz. Don't visit any political sites on the web for your own sake.

No, I mean I try to help out, but personally I could give a rat's ass whether or not you're satisfied with what I have to say. It just doesnt make any sense, to ask for people's help or ideas, and then tell them how you think they're wrong on every count. I mean, what's the point?

as some of us call it here, the stock "BOV" is called the air bypass valve (not to be confused with the bypass air control valve) anyways.... that vents the air back into the intake box....so why would that cause the afm door to shut?? it is designed to vent the air back in, so (and i've seen in other forums, online, elsewhere) that the air bypass valve is a better choice, venting the unused air back to the intake box.... however, those forums/people say there is a limit... the air bypass valve cannot handle such a big pressure from aftermarket turbos, so compression surge may happen, since it cannot route the air back into the intake box in time... (hence we all call it the STOCK bov) and so an atmospheric vent BOV (note: that is why it is called a Blow OFF valve, it blows the air away...(not really blow but u get the idea)) needs to be used and vent the air out to nowhere....

So, if someone gives me their answer, I should accept that even though I don't agree or it does not add up so to speaK? Again, if you read the second to the last post I made......I've obviously given thought that the pressure is indeed slapping at the vane in the afm.

I'm going to drop out answering your replies. This kind of thing can go on and on and on and on. By the way, if I find it is the vane slapping and making that tinkle noise on deceleration, I'll post it as so.

(i'm going to reply to this having never in my entire life seen a stock FC BOV setup)
Sooo.... if it vents to the airbox PAST the AFM, that would cause an insanely rich condition..
Are you sure thats what happens?


Anyhow, it's call a discussions guys... everyones entitled to their own opinion. Thats the whole point of living in a free speach, democratic world.

ps, HAILERS, i'd REALLY like it if you could measure the voltage from the AFM without a BOV.

That would be speech :) Oh, and I haven't heard the "it's a free country" thing since I was 8 but it's STILL entertaining hehe

(I'm just kidding w/ u)

BOV, no BOV...whatever. To make us all happy lets move this to the lounge and turn it into a cleavage thread hehe

I agree. Theres different ways to look at it. So leave it at that. Yet again.

****i'm going to reply to this having never in my entire life seen a stock FC BOV setup)
Sooo.... if it vents to the airbox PAST the AFM, that would cause an insanely rich condition..
Are you sure thats what happens*****

No, not really. The stock air bypass valve has one of its two hoses located between the turbo outlet and the intercooler inlet.........and the other hose going to the duct b/t the afm and the turbo inlet. So it dumps the pressurized air in the duct b/t the turbo outlet and intercooler and feeds it to the duct b/t the turbo inlet and afm or TID. Not prior to the afm inlet. AFTER the afm.

As of 1:48 am this day and having driven the car for about ten miles this day, it seems the vane in the afm is slamming shut. and bouncing. That explains the multiple tinkles I've been hearing. I can boost a bit while staring at the SAFC's voltage readings for the afm, and when I let off the gas, the voltage figures bounce from a high somewhere in the 3 something volts to 1 something volts and it does this several times. It happens rapidly. I can just catch the 3??? volts but can't distinguish the other numerals.

FYI the afm reads approx 3.8volts fully shut with the engine off (memory, best of). I've a meter that can capture the high/low readings and I'll try that the next few days to see how high is and how low low is.

If I don't boost at all, and let off the gas I don't get the tinkle sounds nor the jumping of the voltage on the SAFC. I'm pretty much convinced that is what is happening. I'm gonna take a look at the other car tomorrow or at least pretty soon. Maybe look at it's SAFC with the stock BOV in place ...then cap off the BOV (heck, just cap the vac line to it should do the trick), and see if I get a tinkle/bounce of its afm voltage.

New Apexi bov arrives tomorrow ...sometime they say.

Thank you, thats exactly what I thought happened.

I have never seen a stock bov set up either. Anybody got a picture?

Anyways I have run my car without a bov from my body shop after and it drove fine but I didnt boost at all.

Something I wrote elsewhere... :)

The sole responsibility of the BOV is to prevent "compressor surge".

What is compressor surge?
This is when airflow tries to "backpeddle" over the compressor wheel section.
Normally, the turbo sucks in air and then spits it out into the intercooler / engine.
If there is a spike in pressure after the turbo, the airflow suddenly stops and sometimes actually travels backwards!
If this happens, it's called compressor surge.
You can sometimes hear this as a "fluttering" sound.
Compressor surge is BAD.
You basically try to make a 50,000RPM to 150,000RPM turbo (compressor) wheel stall to a dead stop or even spin in reverse.
In mild circumstances, this puts tremendous load on the thrust bearing on the turbo.
In extreme circumstances, it will tear the compressor wheel off of the shaft.

So why this dangerous situation?
When boosting hard, everytime to lift of the throttle (i.e. to shift on a manual transmission), the throttle plates on the throttle body snaps shut.
The turbo cannot stop on a dime, so it's still trying to pump air into the engine.
But the throttle body slammed shut?
What happens?
There is a huge pressure spike in the entire system between the turbo and the throttle body.
This is where the BOV comes in.
By triggering the BOV, positioned between the turbo and the throttle bodyt, to act like a relief valve in between the throttle body and the turbo, this sudden pressure spike is relieved.
This is why you hear the loud WHOOSH; it is this pressure spike being relieved.

So the BOV is not just there to make "cool noises".
It's there to prevent damage to the turbo from compressor surge. :)


-Ted

So what happens when you are boosting with no BOV and slowly let off the throttle until almost at 0psi or back into vac? Does this bleed off the pressure into the engine? Give the turbo time to stop spooling?

Better go tell those knob heads at Mazdas' R&D dept. that they got it all wrong then I guess hey.. Whatdaya know, nothing to do with noise/emmisions after all hey. :)

So how fast do you think it'd take for a turbo to spool down with a BOV in the inlet tract?

Because it takes about 2-4 seconds at LEAST for it to spool down to close to zero without a BOV.

So what evidence have you come across of compressor surge putting extra side-loadings on the bearings RETed?

Theoretically, this is possible to do.
Realistically, I'd say it's next to impossible to do consistently.
Do you really want to chance damaging the turbo trying to do this? :)


-Ted

This is the consensus from most turbo shops when you ask them this question.
We've done this on purpose years ago and managed to teardown the turbos shortly thereafter.
If you don't know what you're looking for, you wouldn't see the slight damage to the thrust bearing.
After consulting with one of the top west coast turbo rebuilders up in NorCal, we found out what compressor surge damage looked like...


-Ted

But White_FC is a turbo expert is he not? :)

could some explain to me how diesels can operate with no throttle plates?

i am running no BOV. i have only been doing so for a couple of weeks, but everything seems fine so far. :)

I have no idea. :(


-Ted

I hope u got my sarcasm hehe

Extreme damage to thrust bearing - most likely caused by compressor surge...

http://rx7cz.net/photos/workshop101/IMG_3821.JPG
Special thanx to hIGGI for the pics.


-Ted

That doesn't make sense to me either. BUT, ever since I found out diesels can run on vegetable oil, I'd believe anything.

Diesels can opperate with no throttle butterfly because when a diesel is leaned out it behaves quite differently than a conventional spark ignition engine.

Diesel fuel doesn't care how much 'extra' oxygen is in the mixture, it will combust with a close enough to right ammount figure of oxygen and let the rest out of the exhaust.

This is why diesels can be solely controlled by means of fuel delivery.

-----

Anyway, back on topic
No i'm not a turbo expert, never claimed to be..
But I what I AM is someone still waiting for a good reason why compressor surge is bad. Think about this, you have no BOV, compressor surge lasts for 2-4secs.. then think about when you do have a BOV, you let off the throttle, what happens to the turbo RPMS?
How fast is it going after 4secs? bloody close to 2 poofteenths of stuff all.

Now as I said, im certainly no expert, but my idea was that the primary reason for thrust bearing/plate dieing was from the main bearings wearing out causing the wheel/shaft to 'wobble' at high RPMS which in turn, kills the thrust bearing?

Or have I been grosely misinformed?

Thanks for the info. I just wanted to know, not because I thought about doing it.

There is an almost instantaneous spike in boost pressure between the turbo and the throttle plates.
If you don't believe me, try hooking up a pressure sensor in this section and remove any BOV.
It's this pressure spike the shaft (and compressor wheel) to shoot out axially.
Due to the compressor wheel design, the shaft tends to shoot toward the turbine side - stare at the design and you're understand why this is so when the compressor section gets a sudden spike in pressure.
This is what causes damage to the thrust bearing.

High speed wobble should not be a problem if the turbo is properly balanced.
It's the primary responsibility of the oil journal bearings to minimize the wobbling.
Obviously, the balancing helps a lot.
The thrust bearing does not suspend the turbo shaft.
Try take apart a turbo and look at the design.


-Ted

Bov
 

o do i love the sound they make

Where did I say there wasn't a pressure spike?


I am looking at a compressor wheel right at the moment and I can assure you that the majority of the force will be directed radially not axially. If anything the shaft would be 'pulled' to the front.
Have a look at the leading edge of the compressor fin, which way is that pointing?
It's opposite in direction to the thrust plate side of the wheel (the bit I assume your talking about).

Thank you for basically restating what I said?
When the main bearings get loose, the shaft wobbles(regardless of how well it's balanced...) and the wheel can hit the thrust bearing?
So do you not conceed that maybe that pic that you posted of the stuffed thrust bearing was because of a main bearing failure? I know thats what happened to my old S4 turbo...

God we' have already gone over this. Just close this thread.