sick of compressor surge??? Synchronic BOV

[fivebob]

[If you close the throttle when you have no positive pressure, the valve may not be pushed open as there is no major pressure difference across the BOV *but* the compressor could still have some speed on it, pumping more air than the system can use.

But if there is no pressure then there can be no reversal of flow, that against the laws of physics, air moves from high pressure to low pressure, so it that situation you can't get compressor stall.

One way or another, the stall noise is caused by the system failing to use the air - that could be the compressor out pumping the motor, or the compressor pushing against a closed throttle and no open BOV to releive pressure.

Yes, compressor surge/stall is what occurs when the sytems pumps more that is used, but it needs to be way more than is used and, more importantly, the turbine needs to be driving the compressor with some force at the time, or all you actually get is compressor slow down, not the stalling of the airflow.

I stand by my statement that all you are hearing in these videos is valve flutter, not compressor stall.

[fivebob]

rb20det, no bov, made compressor surge noise when throttle closed. Could feel the air flowing back out of the filter.
Turbo was in perfect condition, now stuffed. Seems very compressor surge like to me.

Ahh now I see, poorly designed system at fault, hint, that's what BOV's are for

[touge rolla]

^ lol yeah, he's not that upset it's only a T3

[Lith]

[If you close the throttle when you have no positive pressure, the valve may not be pushed open as there is no major pressure difference across the BOV *but* the compressor could still have some speed on it, pumping more air than the system can use.

But if there is no pressure then there can be no reversal of flow, that against the laws of physics, air moves from high pressure to low pressure, so it that situation you can't get compressor stall.

Pressure is generated from resistance right? The moment the throttle closes, the engine/plenum is removed from the system - there WAS no pressure as the engine was breathing all the air moved by the spinning compressor. Sure, it wasn't in boost - but it was still moving air. Maybe the amount of pressure is too low for the BOV to be opened, and the "flow" is well in the compressor wheels surge zone haha.

With the throttle closed, the engine is replaced by shut throttle plate, a closed BOV and a bunch of piping which is very likely to have far greater resistance than a spinning engine - voila, instant pressure. Or am I missing something? I am just bleating, but just trying to get people thinking.

[Crucible]

Yes, compressor surge/stall is what occurs when the sytems pumps more that is used, but it needs to be way more than is used and, more importantly, the turbine needs to be driving the compressor with some force at the time, or all you actually get is compressor slow down, not the stalling of the airflow.

ok, so what Im describing is just some type of surge not true "Compressor Surge", that makes sense from what youve described. To just clear it up, if you were for example to experiace true compressor surge, it would NEVER be off throttle, definately only during WOT correct?

I stand by my statement that all you are hearing in these videos is valve flutter, not compressor stall

On my car the airfilter is on the drivers side under thr R/F guard, the BOV is situated just before the throttle body in the piping on the pass side, when I get "surge", it is definately on the drivers side (exiting airfilter) definately not from the BOV.
What would be the correct name for this venting flutter Im experiancing do you think?? if its not "comp surge" or "comp stall" or "valve flutter" as its exiting the air filter, what would it be?????

Also, how much of this surge will a turbo take? If this isnt dangerous comp surge like you have described, is it dangerous at all? or nothing to worry about??

[flygt4]

my st185 had no bov fitted and made the above mentioned fluttering.

i now run no blow off valve on my trueno and get the ch ch ch sound out of my air filter. even when i had a poorly functioning bov , it still wasnt releasing all the compressed air and some got back through the compressor and came out the airfilter.

i only run no bov as a shortterm measure. i dont care what anybody says but in my mind air going through the compressor and stalling or slowing it in any way is probably not a good thing.

[Crucible]

in my mind air going through the compressor and stalling or slowing it in any way is probably not a good thing.

haha yeah, thats pretty much how I see it aswell lol,
when I first got my car together, the ssq wasnt working at all, on 14psi it used to make a loud WHAAAAACk!!!!then CHCH ch ch just off WOT.

I was like f#@! that aint right lol,

Big turbo, 1600cc

maybe the whack was the start of Comp Surge?? It sounded like someone shaking sand off a big floor rug, but 100times louder!!! then I brought the Tial type 50mm one.
have yah taken the trueno out for a boost yet??

[escortman]

hmmm mite have to look into this wen i get my car goin, i cant remember it making that noise but it was just a dump pipe exhaust

[gmacrae]

Big difference between compressor surge and compressor stall/reversion guys. Seems like they dont know that

They think their bov is the first true piston type? Turbosmart veeport's been round for years, and most of the cheap valves are basic piston type.

[Tranquil]

Sorta OT but its worth a mention in this thread.


BOV's have been fitted to the vast majority of production road cars as an emission control system. Nothing at all to do with 'protecting' the turbo, Whoever came up with that must have got a A++ marks at marketing school.

Under conditions of hard snap closing of the throttle, you will get some flow reversion through the inlet tract. Which can result in already metered air passing back through the MAF multiple times and subsequently massive overfueling.
Excessive heat, insurficent/contiminated lubricant, over speeding the shaft and FOD damage is what kills turbo's. If your turbo's dieing from comp surge think about running a proper turbo instead of one of those $700 Trademe wing pong pieces of shit.


To get real compressor surge your going to have to be flowing HUGE volumes of gas (either that or your trying to flow huge quantities of air through a cocktail straw). High performance WW2 fighter aircraft engines were one of the original 'surfer's of Comp Surge. A sudden transition from high altitude flight to low altitude flight at maximum engine rating resulted in big changes in total airflow ingestion. All of a sudden your engine is flowing X times more air through the supercharger or turbo supercharger which the engine cannot consume. You get airflow bouncing off the inlet valves and reversing. This results in a high pressure area in front of the compressor which in turn puts more load on the supercharger gear's or the shaft of the turbo supercharger.
For fast road applications, comp surge is effectivly not an issue. A t04e compe at 3 bar strapped to a 20cc leaf blower engine could be a problem

[touge rolla]

Under conditions of hard snap closing of the throttle, you will get some flow reversion through the inlet tract. Which can result in already metered air passing back through the MAF multiple times and subsequently massive overfueling.

This would not apply to a flap type afm as any backflow of air would simply close it.

And, most stock BOV's are plumbed back into the intake, meaning some of this air would pass back as well? Or would it only prevent more air from entering the system. Vent to atmosphere BOV's cause over-fueling by discarding a quantity of air to the atmosphere that the ECU has measured as going into the motor and therefore supplied the fuel to match it. The only purpose i can see for a plumbback BOV is to prevent surge/stall/reversal by equalising the air pressure across both sides of the turbo.

[~SlideWays~]

Haven't read the whole thread but, Im using a basic GFB bov, its a $295 job... well it was a couple of years ago. I think it may be a "Mach 1" or something along those lines.

This seems to work well, I run 17psi and its sweet. I have definitely heard the surge/chatter before because my very first 4agte setup had no bov at all...it was just an experimental setup anyway.

Only problem I've had is when the tuner, of my current set up, changed some of the plumbing and tee'd the BOV and Wastegate off the same hose. As soon as I got the car back from its tune I thought...wtf why is the bov now sounding different...

I then changed the plumbing back so the BOV had its own line coming from a decent diameter air outlet and it performs much better, it opens even if the turbo had just started spooling.

So simple seems to be better in the case of BOV's in my opinion.


My 10c...for what its worth

[matt dunn]

So simple seems to be better in the case of BOV's in my opinion.


My 10c...for what its worth

I am tending to agree,

i run a tial style 50mm one, and have also tried the genuine tial off the focus, and believe i'd be better off with the old first version turbosmart one that i used to have that would be almost 10 years old now.

i have made a tester for the tial flanged ones and am in the process of trying to get them work efficently and at the correct pressures.

Matt

[mr30%jr]

lol all the suub fans love the bov chater

[matt dunn]

wel I fitted the wastegate spring that came with my Tial wastegate into the BOV and re fitted it and now the BOV is 100 x better.
You can hear it open between changes and the lag between gears is gone.

matt

[escortman]

i had always thought that chchchch was my hks bov as isnt that the noise they make when ur not going hard?

[touge rolla]

^sometimes, oftem people have them setup too hard though and they don't open unless your giving it heaps.

[escortman]

ook so which is hard and which is soft? winding it in makes it softer or harder? mines a 'style' 1 which im thinking of ditching anyway for a racepro blaster or something simple

[touge rolla]

clockwise=harder

[SUBARUCONVERT]

i run no BOV on my subaru, TD05/6, FMIC. u get huge chatter from the filter and chuuu noise on full boost higher rpm shifts. i would benefit from a re-cric BOV as i feel some lag in the lower gears after shifts. but i get no comp surge at all. but there must be alot of comp slowing happening (exhaust flow being cut, then comp pushing against a closed throttle)