Is a BOV really needed?
03-11-03, 08:46 PM
#1
kortez
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Is a BOV really needed?
I had an interesting conversation with one of the larger turbo builders here at a local race last weekend. Since I went to a larger turbo (T66), I am having problems with my BOV leaking and comp surge so i asked him how important a BOV is... He said I don't really need one and they see more turbo failures due to BOV related problems than anything else. They leak and cuase the turbo to over-rev, and they surge and do damage from that. Obviously a BOV is a good idea in theory, but its seems they may be cuasing more harm than good.
So do all of you run with one or are there some out there that would agree?
So do all of you run with one or are there some out there that would agree?
03-11-03, 09:13 PM
#2
fart on a friends head!!!
the only one that i have heard of that has been used w/o a bov is the rx6 turbo. its a bear as far as durability. if you didnt have a bov, they youd have comp. surge all the time. so get a good one. . . theres your solution.
paul
edit: if yours is adjustable, then try that first. it may be too loose for your setup. the bov is there to help. . . make sure its in good working order and your safe.
paul
edit: if yours is adjustable, then try that first. it may be too loose for your setup. the bov is there to help. . . make sure its in good working order and your safe.
03-12-03, 03:10 AM
#5
There are a lot of reports of BOVs leaking. They don't all leak, though. I don't think my Tial leaks, and there are some other "good" ones that people seem to like. Perhaps many of the BOVs are designed for lower boost applications and noisy blow off action.
You'll get surge if you don't have a BOV with any turbo. BB turbos are said to be able to take this load on the bearings better than standard bearing turbos, but I still thought it was a good idea to add a BOV to reduce the stress on the turbo plumbing and the turbo. I don't know if it is really necessary, however. I did run without it for a while and it sounded like the Three Stooges when I let off -- wub-bub-bub-bub-bub.
-Max
You'll get surge if you don't have a BOV with any turbo. BB turbos are said to be able to take this load on the bearings better than standard bearing turbos, but I still thought it was a good idea to add a BOV to reduce the stress on the turbo plumbing and the turbo. I don't know if it is really necessary, however. I did run without it for a while and it sounded like the Three Stooges when I let off -- wub-bub-bub-bub-bub.
-Max
03-12-03, 04:13 AM
#6
Banned. I got OWNED!!!
On my data logs I could not tell the difference between a BOV and no BOV (in terms of pressure spikes or fluctuations between gear shifts or when backing off). i ran with one at one stage then with out one for a long time, then I decided to hook it back up. everytime I could not see any difference in the data recorded by the computer.
The boost responce was the same the lag was no greater and, though there was a great difference in sound ! I prefer the wastegate sound to the BOV, have very fond memories of hearing an S2 Audi Quattro rally car going up Pikes Peak and hearing an awsome WG sound, same on Rod Milens Celica just not as piercing, heaps and heaps of Ford Sierra's running 36+psi running no BOV just the WG too, I rekon the sound is awesome
Heaps of old style Group C endurance racers only ran WG too and they seemed to live for 24 hour endurance races with out issues. Lots of significant race cars never ran one and seemed to be very reliable, F1 cars never ran them when using plain bearing turbos.
Interesting question, I wonder why they were never used in these advanced applications ? may tend to agree with what that race guy told you at the track ? Just another part that can fail I suppose....... and the benifits don't out number the risks
The boost responce was the same the lag was no greater and, though there was a great difference in sound ! I prefer the wastegate sound to the BOV, have very fond memories of hearing an S2 Audi Quattro rally car going up Pikes Peak and hearing an awsome WG sound, same on Rod Milens Celica just not as piercing, heaps and heaps of Ford Sierra's running 36+psi running no BOV just the WG too, I rekon the sound is awesome
Heaps of old style Group C endurance racers only ran WG too and they seemed to live for 24 hour endurance races with out issues. Lots of significant race cars never ran one and seemed to be very reliable, F1 cars never ran them when using plain bearing turbos. Interesting question, I wonder why they were never used in these advanced applications ? may tend to agree with what that race guy told you at the track ? Just another part that can fail I suppose....... and the benifits don't out number the risks
03-12-03, 08:15 AM
#7
WTF is wrong with it now?
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How did your boost response during and after shifting look RICE? This is a topic I am interested in, as I don't have one right now. The TiAL is about $500 CDN and I wouldn't buy any of the cheaper ones anyway.
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03-12-03, 08:26 AM
#8
I will comment that I have a TiAl and I still get compressor surge upon initial lift of the throttle. I have had all three spings that they offer. THe heaviest didn't open at all, the middle one opened after TONS of wub, wub, wub and the latest, "rotary specific" one still surges slightly. On top of that the valve flutters open/closed at idle, due I assume, to the heavy street port that I have.
I had a turbo XS type "H" initiallly, from which I "upgraded" to the TiAl. The XS worked flawlessly and I never had any problems. I have considered switching back.
I had a turbo XS type "H" initiallly, from which I "upgraded" to the TiAl. The XS worked flawlessly and I never had any problems. I have considered switching back.
03-12-03, 11:15 PM
#9
I am having problems with my BOV leaking and comp surge so i asked him how important a BOV is... ------------------------------------------------------------------------
it's not the BOV that leaks it's from your turbo leaking! and it's essential to have one unless you wanna kill your turbo!
it's not the BOV that leaks it's from your turbo leaking! and it's essential to have one unless you wanna kill your turbo!
03-12-03, 11:30 PM
#11
Banned. I got OWNED!!!
Lets think about this for a second.
Why will your turbo be destroyed sooner without a BOV ? a thrust bearing is designed to take a certain amount of designed load at maximum boost, all that happens when you run the WG is that the thrust pulses down>down>down>down> just as reflected on a data logger 15psi WG setting may start to open at 10psi so the turbo is making 15psi, you shut the throttle the WG opens, boost drops WG closes, boost goes up WG opens and so on till there is no more boost pressure to open the gate at it's lowest spring opening pressure. Surley this cannot cause so much damage to the thrust bearing ?
I have never loged a boost spike when not running the BOV valve, and I have never measured a noticable delay in boost pressure build up after a change of gear with the BOV bypassed. So I am having trouble seeing the exact problem, I mean for years and years WG was all that was used on every race. And many production cars too. I think the first production sports car I saw with a BOV was a Ferrari F40 in 1987 Ironically they came out with RX6 IHI Turbos
Why will your turbo be destroyed sooner without a BOV ? a thrust bearing is designed to take a certain amount of designed load at maximum boost, all that happens when you run the WG is that the thrust pulses down>down>down>down> just as reflected on a data logger 15psi WG setting may start to open at 10psi so the turbo is making 15psi, you shut the throttle the WG opens, boost drops WG closes, boost goes up WG opens and so on till there is no more boost pressure to open the gate at it's lowest spring opening pressure. Surley this cannot cause so much damage to the thrust bearing ?
I have never loged a boost spike when not running the BOV valve, and I have never measured a noticable delay in boost pressure build up after a change of gear with the BOV bypassed. So I am having trouble seeing the exact problem, I mean for years and years WG was all that was used on every race. And many production cars too. I think the first production sports car I saw with a BOV was a Ferrari F40 in 1987 Ironically they came out with RX6 IHI Turbos
03-12-03, 11:54 PM
#13
Banned. I got OWNED!!!
Look I'm f*cked if I know, I have had a long day at work and am real tired !
I can see the negative effect of the thrust load pulsing up & down in quick sequence, but it escapes me at the moment as to how this will damage the turbo much faster than one equiped with a BOV........ though I am sure that a nice even droping thrust load is better than one that pulses up and down while getting lower, the differences on paper would be marginal at best ? I guess this is why you never saw these devices in the pinical of motor sport or on endurance racers as it realy did not effect the life to a great deal ?
I can see the problems of a BOV failing for sure casue this can over stress the turbo very easily as it will not see the pressure through the WG and hence regulate the turbine/compressor ultimate speed. Maybe this is why you never saw these devices on real serious race cars ???
I can see the negative effect of the thrust load pulsing up & down in quick sequence, but it escapes me at the moment as to how this will damage the turbo much faster than one equiped with a BOV........ though I am sure that a nice even droping thrust load is better than one that pulses up and down while getting lower, the differences on paper would be marginal at best ? I guess this is why you never saw these devices in the pinical of motor sport or on endurance racers as it realy did not effect the life to a great deal ?
I can see the problems of a BOV failing for sure casue this can over stress the turbo very easily as it will not see the pressure through the WG and hence regulate the turbine/compressor ultimate speed. Maybe this is why you never saw these devices on real serious race cars ???
03-13-03, 12:07 AM
#14
RICE, opening the wastegate doesn't lower the boost quite like it normally does if the throttle is closed. My understanding is that you have a turbo spinning really fast and then you snap the throttle shut, the turbo is still pumping a lot of air, so you get a pressure spike in the intake tract between the turbo and throttle, and then you get some oscillations as the air surges back to the turbo, back to the throttle, back to the turbo, back to the throttle... That might be why the wastegate seems to oscillate without a BOV installed. If you are logging manifold pressure, it probably won't show the spikes since the sensor is between the throttle and the engine and the spikes are between the turbo and the throttle. Closing the throttle when the turbo is spinning really fast is supposed to put a lot of load on the bearings since the air has nowhere to go, and the surge of air bounces off the throttle and then back to the turbo.
That is my understanding of what happens. I don't know how much more load that places on the turbo, but it seems like it would be quite a bit more than what you get at max boost with the throttle open. It isn't clear if the increased load is bad for the turbo, but it seems likely that it at least increases the stress versus having a properly-functioning BOV. It still may not be enough to cause any problems, though, so that might be a bit of a moot point.
I get a little bit of surge on occasion with my Tial BOV, but it is way less than without it. The surge is evident from the WG noise. It doesn't bother me much since the turbo is supposed to be strong enough to run BOV-less. I do think the BOV reduces the stress on my turbo hose couplings and piping, and that is part of why I run it. I don't know if it has any effect on spool up time after a shift, but from your data I wouldn't expect it to be a noticeable difference.
-Max
That is my understanding of what happens. I don't know how much more load that places on the turbo, but it seems like it would be quite a bit more than what you get at max boost with the throttle open. It isn't clear if the increased load is bad for the turbo, but it seems likely that it at least increases the stress versus having a properly-functioning BOV. It still may not be enough to cause any problems, though, so that might be a bit of a moot point.
I get a little bit of surge on occasion with my Tial BOV, but it is way less than without it. The surge is evident from the WG noise. It doesn't bother me much since the turbo is supposed to be strong enough to run BOV-less. I do think the BOV reduces the stress on my turbo hose couplings and piping, and that is part of why I run it. I don't know if it has any effect on spool up time after a shift, but from your data I wouldn't expect it to be a noticeable difference.
-Max
03-13-03, 12:14 AM
#15
WTF is wrong with it now?
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I like the way RICE looks at this. Do the datalogging. I'm buying an E11 this month, so I will try it on the 200 samples per second rate and see what happens. I would have to add a second sensor upstream of the TB, though.
Relying on the wastegate to regulate this between shifts might not be the best way, though. The wastegate regulates the SPEED of the turbo only. Any boost spike during a sudden throttle plate closing would be from the compressor spinning at full speed suddenly meeting a lot more resistance. The inertia of the wheels at high speed would be the problem. Torque being applied to the turbine would not really cause the boost spike, cause the wastegate would open like you said and take away the energy being applied to the compressor.
In other words, what MAX said while I was typing this. I need to learn to type and think faster.
Another potential problem would be if you have an electronic boost controller. The EBC would see vacuum, because it is measuring after the TB. It would not allow the wastegate to open, because the solenoid would be applying boost to both sides, right?
Even endurance racing could stand to go without a BOV, I think, because they likely re-build the turbos after every race, if not throw them away.
Datalogging the boost pressure @ high speed before the throttle plates is the best way to tell. The noise would imply a shock wave travelling through the intake charge, though.
Relying on the wastegate to regulate this between shifts might not be the best way, though. The wastegate regulates the SPEED of the turbo only. Any boost spike during a sudden throttle plate closing would be from the compressor spinning at full speed suddenly meeting a lot more resistance. The inertia of the wheels at high speed would be the problem. Torque being applied to the turbine would not really cause the boost spike, cause the wastegate would open like you said and take away the energy being applied to the compressor.
In other words, what MAX said while I was typing this. I need to learn to type and think faster.
Another potential problem would be if you have an electronic boost controller. The EBC would see vacuum, because it is measuring after the TB. It would not allow the wastegate to open, because the solenoid would be applying boost to both sides, right?
Even endurance racing could stand to go without a BOV, I think, because they likely re-build the turbos after every race, if not throw them away.
Datalogging the boost pressure @ high speed before the throttle plates is the best way to tell. The noise would imply a shock wave travelling through the intake charge, though.
03-13-03, 06:32 AM
#18
Banned. I got OWNED!!!
Max is right, you need to log before the TB as well. I was doing a different method, in conjuction with the MAP logging (after the TB) I was using an absolute pressure gauge reading the signal between the IC and the TB (the same take of for the WG line) and I was doing a visual on any boost spiking between shifts, I did not notice any at all.
I tried this test on a TO4S turbo running 20psi (472rwhp) the gauge was quite a large face absolute pressure unit and it was reading around 2.3bar absolute as soon as the throttle was closed the boost droped in a series of pulses which followed the classic WG noise, the pressure did not spike over the WG setting.
The boost responce was measured of the map logging on the ecu and I could not determine a difference between BOV and WG pressure release effect on spool up. have to admit I am addicted to the WG noise especially at high boost when it is a real piercing series of whistles My friend just bought a second hand TO4S of a guy who had been running 20 to 23psi all the time just with a WG and it measured normal thrust clearance to a "newish" unit run on a BOV at lower boost, it had done about 10000km of street driving and a fair bit of street racing
I tried this test on a TO4S turbo running 20psi (472rwhp) the gauge was quite a large face absolute pressure unit and it was reading around 2.3bar absolute as soon as the throttle was closed the boost droped in a series of pulses which followed the classic WG noise, the pressure did not spike over the WG setting.
The boost responce was measured of the map logging on the ecu and I could not determine a difference between BOV and WG pressure release effect on spool up. have to admit I am addicted to the WG noise especially at high boost when it is a real piercing series of whistles
My friend just bought a second hand TO4S of a guy who had been running 20 to 23psi all the time just with a WG and it measured normal thrust clearance to a "newish" unit run on a BOV at lower boost, it had done about 10000km of street driving and a fair bit of street racing
03-13-03, 05:56 PM
#19
Old [Sch|F]ool
Wow, this goes aginst everything I've been brought up to believe. Seeing pictures of compressor wheels spread apart like Elmer Fudd's shotgun because of heavy compressor surge, shafts snapped in half, etc...
Seeing pictures of compressor wheels spread apart like Elmer Fudd's shotgun because of heavy compressor surge, shafts snapped in half, etc...
03-13-03, 06:11 PM
#20
Banned. I got OWNED!!!
Yeah, when you see a 1985 BMW or Hart powered car running a T51 sized turbo pushing 4 bar gauge boost pressure and ONLY running a WG it tends to put a major flaw in some of those dooms day stories people go on about today.
Faned out compressor wheels from what I have seen will only happen from massive over speed of the turbo (ie faulty BOV etc?) similar for a snapped shaft, I have seen this happen due to extreme heat stress (pushing allot of power) on a too small a frame size turbo.
But yeah I just don't see how these failures would happen because you did not run a BOV, surley 4+BAR (gauge pressure) in F1 back in the day would have poped every single turbo if this were the case, History shows it just was not an issue at all. And it begs the question why in the hell did they not run any type of system like a BOV from 1980 to 1986 (they were forced to run pop off valves from 87 to 88 to limit boost) ??? I think ALL of the respective people and companies involved over that time frame would have been using BOV's if they offered the benifits people talk about today....
BOV or not ? Interesting question
Faned out compressor wheels from what I have seen will only happen from massive over speed of the turbo (ie faulty BOV etc?) similar for a snapped shaft, I have seen this happen due to extreme heat stress (pushing allot of power) on a too small a frame size turbo.
But yeah I just don't see how these failures would happen because you did not run a BOV, surley 4+BAR (gauge pressure) in F1 back in the day would have poped every single turbo if this were the case, History shows it just was not an issue at all. And it begs the question why in the hell did they not run any type of system like a BOV from 1980 to 1986 (they were forced to run pop off valves from 87 to 88 to limit boost) ??? I think ALL of the respective people and companies involved over that time frame would have been using BOV's if they offered the benifits people talk about today....
BOV or not ? Interesting question
03-14-03, 12:11 AM
#21
kortez
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I am going to run mine without and see what happens. One less thing to fail and make trouble sounds good to me.
I don't mine the wub wub wub sound... I love The Three Stooges!
I don't mine the wub wub wub sound... I love The Three Stooges!
03-14-03, 02:23 AM
#24
Old [Sch|F]ool
I'd also much rather hear a compressor surge giggle than some prissy "pschoooo" blow off valve... but it's still hard for me to work it into my head that compressor surge isn't that bad.
It's kinda like my roommate, whose 472 Cad motor has bad main bearings. He likes the sound, says it sounds like a freight train.
Marshall... for what it's worth, GNs have automatics. You don't have to close throttle to shift on a hard acceleration run. Since a turbo's speed is more related to pressure ratio than it is total airflow (with a decently broad compressor map anyway), when the RPM drops it doesn't really result in a big boost spike. Which a BOV wouldn't be able to do anything about anyway, since they need a manifold vacuum to work...
It's kinda like my roommate, whose 472 Cad motor has bad main bearings. He likes the sound, says it sounds like a freight train.
Marshall... for what it's worth, GNs have automatics. You don't have to close throttle to shift on a hard acceleration run. Since a turbo's speed is more related to pressure ratio than it is total airflow (with a decently broad compressor map anyway), when the RPM drops it doesn't really result in a big boost spike. Which a BOV wouldn't be able to do anything about anyway, since they need a manifold vacuum to work...
Last edited by peejay; 03-14-03 at 02:29 AM.
