BOV what's the point
- Thread starter NashMan
- Start date
when your boost it, let off the gas and clutch really quick all of that air is then rushing back to the turbo... and wouldnt that just cause MORE harm then good?
i know on an auto, you just smash the gas pedal... the throttle plate never closes, so i can see why you wouldnt need a BOV.
like shaeff said, could the blades take the backpressure being created?
Nash - do you have anything to log the boost and 0-60/80/100mph times your getting? or is it just from the gauges and butt dyno?
i know on an auto, you just smash the gas pedal... the throttle plate never closes, so i can see why you wouldnt need a BOV.
like shaeff said, could the blades take the backpressure being created?
Nash - do you have anything to log the boost and 0-60/80/100mph times your getting? or is it just from the gauges and butt dyno?
ummm no i have no testing stuff hell i have bhg lol
you can really just feel the diff you don't loose power between shifts kinda like an auto
see what compsures surge is shock wave that runs down the intake stream
the diff between teh 2 as in damge is not as much as you think it is
you can really just feel the diff you don't loose power between shifts kinda like an auto
see what compsures surge is shock wave that runs down the intake stream
the diff between teh 2 as in damge is not as much as you think it is
ok i dug some thing up that i cna post cause it is hard to post book's that i have no scanner lol
any way
So how often have you see a BOV actually tested for its ability to reduce the pressure spike that occurs when you shut the throttle on a hard-blowing turbo? Not very often, right? And in fact, what does that pressure spike actually look like?
We decided to do some high-speed logging of the pressures that occur in the intake system between the turbo and the throttle blade when you snap the throttle shut. We used a Fluke 123 digital Scope meter and a Fluke pressure transducer.
This screen grab shows the pressures with the electronically controlled Goyen BOV working. Each vertical division is the equivalent of 20 kPa (about 3 psi) manifold pressure and each horizontal division is 200 milliseconds. So from far left, the car is holding 70 kPa, grading down slightly to 60 kPa (about 9 psi) before the throttle is suddenly closed. The pressure abruptly spikes by 10 kPa (about 1.5 psi) but the spike is very short-lived (about 50 milliseconds) before it rapidly and smoothly falls away. In fact, the pressure drops from the spike of 70 kPa down to 20 kPa in less than 100 milliseconds (ie one tenth of a second). The fall to less than 10 kPa takes about 650 milliseconds (ie 0.65 seconds) in total.
And what a different story there is without the BOV working
Again the throttle was abruptly closed at 60 kPa boost. The immediate pressure spike was about 15 kPa (only a little higher than without the BOV) but what follows from there is completely different. Rather than dying away quickly, the pressure is both much slower to fall off and is also accompanied by very rapid pressure waves, with these waves starting off at about 20 kPa peak-to-peak and then gradually dropping to about 10 kPa. The frequency of these varies from 15-20Hz. In other words, there is a pressure wave of up to 20 kPa racing up and down the intake system between the throttle and the turbo. It is very likely that this wave battering against the turbo compressor is potentially much more damaging that the initial pressure spike itself. Also note that the trapped pressure takes a lot longer to decrease – to drop to 20 kPa takes about 500 milliseconds (half a second) compared with one-fifth of that when a BOV is fitted."
with this all said and done the newer gt series turbo should not have any probs wiht this at all now as for the t series turbo i am still not sure
see i notice some thing odd long ago whe the gt40's and the gt42's were comeing out there houseing were not drilled none of them we even asked our suppler if he chould get one he said to us never have one ever that was drilled
makes you raise an eye brow don't it like it not needed
any way
So how often have you see a BOV actually tested for its ability to reduce the pressure spike that occurs when you shut the throttle on a hard-blowing turbo? Not very often, right? And in fact, what does that pressure spike actually look like?
We decided to do some high-speed logging of the pressures that occur in the intake system between the turbo and the throttle blade when you snap the throttle shut. We used a Fluke 123 digital Scope meter and a Fluke pressure transducer.
This screen grab shows the pressures with the electronically controlled Goyen BOV working. Each vertical division is the equivalent of 20 kPa (about 3 psi) manifold pressure and each horizontal division is 200 milliseconds. So from far left, the car is holding 70 kPa, grading down slightly to 60 kPa (about 9 psi) before the throttle is suddenly closed. The pressure abruptly spikes by 10 kPa (about 1.5 psi) but the spike is very short-lived (about 50 milliseconds) before it rapidly and smoothly falls away. In fact, the pressure drops from the spike of 70 kPa down to 20 kPa in less than 100 milliseconds (ie one tenth of a second). The fall to less than 10 kPa takes about 650 milliseconds (ie 0.65 seconds) in total.
And what a different story there is without the BOV working
Again the throttle was abruptly closed at 60 kPa boost. The immediate pressure spike was about 15 kPa (only a little higher than without the BOV) but what follows from there is completely different. Rather than dying away quickly, the pressure is both much slower to fall off and is also accompanied by very rapid pressure waves, with these waves starting off at about 20 kPa peak-to-peak and then gradually dropping to about 10 kPa. The frequency of these varies from 15-20Hz. In other words, there is a pressure wave of up to 20 kPa racing up and down the intake system between the throttle and the turbo. It is very likely that this wave battering against the turbo compressor is potentially much more damaging that the initial pressure spike itself. Also note that the trapped pressure takes a lot longer to decrease – to drop to 20 kPa takes about 500 milliseconds (half a second) compared with one-fifth of that when a BOV is fitted."
with this all said and done the newer gt series turbo should not have any probs wiht this at all now as for the t series turbo i am still not sure
see i notice some thing odd long ago whe the gt40's and the gt42's were comeing out there houseing were not drilled none of them we even asked our suppler if he chould get one he said to us never have one ever that was drilled
makes you raise an eye brow don't it like it not needed
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so the first pic is NO bov, and the second pic is WITH the bov?
interesting findings though. im really interested to know if you can run certain turbos with no BOV's...
interesting findings though. im really interested to know if you can run certain turbos with no BOV's...
Even if you can, I can't think of any way that a functioning BOV can hurt, and I can easily think of ways that it can help.
that is some interesting stuff nash, and better throttle response is tempting.....but who will be the guinea pig with a spare turbo laying around???
you cant do this to a STOCK turbo. its for NEW turbos designed not to surge like older turbos. you have to consider this when reading through the info.
if you think a stock ct doesnt need a BOV... thats just being dumb.
if you think a stock ct doesnt need a BOV... thats just being dumb.
Dan_Gyoba;981851 said:
Makes it difficult to shift smoothly because of the moment it runs rich between when you hit the clutch. Thats my biggest complaint.
if your running rich between shifts then your bov isnt recirculating back into the intake post-AFM.
Okay, then let me rephrase. I can't think of a way that a properly functioning BOV can hurt.TurboWarrior;981977 said:
If you're running an AFM, then your BOV has to be recirculated to be considered properly functioning. If you're running a MAP system, then that's a sifferent matter.
I will be installing an SSQV, but I have the recirculation fitting for it, for use until or unless I get something like a MAF-T pro.
I agree with Dan Gyoba, if running without a BOV doesnt hurt, running with one setup properly, definately won't hurt. I think it'll help prolong compressor life. ive seen people snap compressor wheels with stock bypass valves..
And you know where the shrapnel from the compressor wheel goes once it snaps, right? 
Just hope you've got an intercooler in the way of the throttle body so it will take the biggest hit. I'd rather sacrafice an intercooler than a motor...
Just hope you've got an intercooler in the way of the throttle body so it will take the biggest hit. I'd rather sacrafice an intercooler than a motor...
If you dont wanna loose your boost tighten up the bov tension spring by adding washers. I prefer to let the pressure out for safety of not killing my suuups, but if your die hard enough have at it because there's great throttle response with a tighter spring.:evil2:
yes this is the hole point of the thread
not haven to recompess the charge pipes
me my self have not bean runing one for the last couple of days
but i have noticed any thing bad so far when i took peek at the turbo
not haven to recompess the charge pipes
me my self have not bean runing one for the last couple of days
but i have noticed any thing bad so far when i took peek at the turbo
7thousandpiecesMGTE;981898 said:
My turbo was ran for quite some time without a BOV, and has moderate shaft play... probably encroaching on the end of it's lifespan. If whether or not having a BOV had a big effect on this, I don't know. It certainly sounds like someone threw an old boot into the turbine when I close the throttle to shift though, with no BOV...
Another thing not mentioned thus far is that the turbine [exhaust] side slows significantly once the throttle plate is closed, as that there's a sudden drop in exhaust gases... though the engine may still be tearing along at high rpm; the throttle plate is closed and not much fuel is around to make hot exhaust gas to spin the turbine. Just a thought anyway...
Nash has some interesting info... the pressure wave oscilliating between the throttle plate and the compressor side, seems to make alot of sense.
Another thing not mentioned thus far is that the turbine [exhaust] side slows significantly once the throttle plate is closed, as that there's a sudden drop in exhaust gases... though the engine may still be tearing along at high rpm; the throttle plate is closed and not much fuel is around to make hot exhaust gas to spin the turbine. Just a thought anyway...
Nash has some interesting info... the pressure wave oscilliating between the throttle plate and the compressor side, seems to make alot of sense.
I guess then that the question comes into play:
Which takes more time/energy? Re-compress less than 1 cubic foot of volume for the IC/piping, or get the turbo spinning again after it's been pushed to a dead halt by surge.
The BOV, when open, allows the turbo to keep spinning, because it's not working against any pressure. It's not getting much power from the exhaust turbine, since the throttle is closed, so that pressure is trying to vent somewhere. The only way that it's getting out past the turbine is by getting it to either stop, or at least slow down a lot.
That means that the engine has to build up some exhaust pressure before it can get the turbine spinning again, and it has to overcome inertia.
The "saved" pressurised intake is good for less than 20ms. Do you think that the engine can get the turbine back up to speed in that time? Nope. So you've got to re-spool the turbo anyway.
Which takes more time/energy? Re-compress less than 1 cubic foot of volume for the IC/piping, or get the turbo spinning again after it's been pushed to a dead halt by surge.
The BOV, when open, allows the turbo to keep spinning, because it's not working against any pressure. It's not getting much power from the exhaust turbine, since the throttle is closed, so that pressure is trying to vent somewhere. The only way that it's getting out past the turbine is by getting it to either stop, or at least slow down a lot.
That means that the engine has to build up some exhaust pressure before it can get the turbine spinning again, and it has to overcome inertia.
The "saved" pressurised intake is good for less than 20ms. Do you think that the engine can get the turbine back up to speed in that time? Nope. So you've got to re-spool the turbo anyway.