HAILERS

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.

White_FC

(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.

jon88se

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

RotaryWeaponSE7EN

iTrader: (6)

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

HAILERS

****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.

White_FC

Thank you, thats exactly what I thought happened.

ilike2eatricers

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.

RETed

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

ilike2eatricers

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?

White_FC

Better go tell those **** 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?

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

RETed

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

jon88se

But White_FC is a turbo expert is he not?

jacobcartmill

iTrader: (6)

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

jacobcartmill

iTrader: (6)

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

RETed

I have no idea.


-Ted

jon88se

I hope u got my sarcasm hehe

RETed

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


Special thanx to hIGGI for the pics.


-Ted

jon88se

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

White_FC

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?

ilike2eatricers

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

RETed

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

tecknomage

o do i love the sound they make

White_FC

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...

RotaryWeaponSE7EN

iTrader: (6)

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