highboostgn
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I thought of this when I ran mine; If you let the air escape through the BOV then wouldn't this hinder performance by letting air out that has already been calculated for by my MAF
GN and bov's???
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84BuickGNYorkPA
Daily Driving Buick V-6 Turbo's 1979 - Present
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It seems simple to me, why would you want your turbo spinning opposite directions everytime you close the throttle after going WOT? Unnecessary stress on the turbo in every area including the blades, bearings and shaft. I put a BOV on my car, and a turbo saver, as stated above, the turbo's today are $$$$
Chuck
Chuck
Let's address a few things brought up here...
First, the experienced members on this board "don't talk about idling your car before shutting it off to cool the center section" because we all know this. If somebody posted the question, "should I?", many people would reply "yes". Common sense if you have any knowledge about turbos.
Second, your turbo does not spin backwards when you close the throttle. The compressor goes into rotating stall when the turbo is spooled up and the throttle is closed. Look at a compressor map for any turbo - when it is spooled up and the throttle is closed, it's being asked to operate at a point on the upper left corner of the map (high pressure ratio with low mass flow rate) which is to the left of the surge line on the map. The compressor goes into rotating stall until it slows down enough to get itself back on the map to the right of the surge line. This causes some light pressure surging through the compressor (watch your boost gauge while this is happening) and the funny sneezing noise.
On most newer stock cars, a BOV is used to prevent the turbo from going into rotating stall. I have a 2011 Sonata with the 2.0L turbo engine, and it has a BOV. A BOV does some good things - it keeps the engine running nice and smooth (the engine doesn't buck back and forth during surge), it makes it easier to continue supplying the correct fueling (good for emissions), it keeps the turbo spooled a little longer during manual transmission shifts, and it prevents a noise that an average customer would find objectionable (the sneezing sound). A BOV probably helps the bearings a little, since the direction of the loading on the bearings rapidly changes direction during the pressure surging that happens during rotating stall.
Do you "need" a BOV on a TR? It depends on your combo. I would say that the larger you turbo compressor, the more likely a BOV will help your bearings. I run a TA49 with a combo that makes it surge a lot without a BOV, yet it has lived a long happy life under pretty severe conditions, and I bought it used in about 2003.
Good luck,
Mike
Sent from my HTC Droid Incredible using Turbo Buick
First, the experienced members on this board "don't talk about idling your car before shutting it off to cool the center section" because we all know this. If somebody posted the question, "should I?", many people would reply "yes". Common sense if you have any knowledge about turbos.
Second, your turbo does not spin backwards when you close the throttle. The compressor goes into rotating stall when the turbo is spooled up and the throttle is closed. Look at a compressor map for any turbo - when it is spooled up and the throttle is closed, it's being asked to operate at a point on the upper left corner of the map (high pressure ratio with low mass flow rate) which is to the left of the surge line on the map. The compressor goes into rotating stall until it slows down enough to get itself back on the map to the right of the surge line. This causes some light pressure surging through the compressor (watch your boost gauge while this is happening) and the funny sneezing noise.
On most newer stock cars, a BOV is used to prevent the turbo from going into rotating stall. I have a 2011 Sonata with the 2.0L turbo engine, and it has a BOV. A BOV does some good things - it keeps the engine running nice and smooth (the engine doesn't buck back and forth during surge), it makes it easier to continue supplying the correct fueling (good for emissions), it keeps the turbo spooled a little longer during manual transmission shifts, and it prevents a noise that an average customer would find objectionable (the sneezing sound). A BOV probably helps the bearings a little, since the direction of the loading on the bearings rapidly changes direction during the pressure surging that happens during rotating stall.
Do you "need" a BOV on a TR? It depends on your combo. I would say that the larger you turbo compressor, the more likely a BOV will help your bearings. I run a TA49 with a combo that makes it surge a lot without a BOV, yet it has lived a long happy life under pretty severe conditions, and I bought it used in about 2003.
Good luck,
Mike
Sent from my HTC Droid Incredible using Turbo Buick
Who has ever worn out a turbo because they didn't have a BOV? Anyone running a big enough turbo to need one isn't street driving, and those that are, still won't see enough miles to wear out a bearing. Oils today are superior as well and coking is less of an issue and thus idle time isn't needed either unless you JUST got done heating it up. I have 40k miles on my TE44 at no less than 20psi, EVER, and a lot of time at 25psi and there is still no shaft play, and I don't have a BOV. I'm already thinking of my next turbo so why do I need to spend money to make this one last any longer than it already will on it's own with good oil and factory boost control setup? BOV's probably do help, and new production turbos use them b/c most consumers don't like the sneeze noise, and they have 100k mile warranties now, but do you NEED one a turbo Buick because that's what everyone else does? No. I'll believe you need one when someone demonstrates that a turbo was harmed in an unreasonable time frame from not having one.
Cavitation is typically only talked about referring to water as the medium. It is waves of extremely high pressure and low pressure stacked up against each other. In my opinion, this is similar to what is happening when the throttle is closed rapidly and the high pressure air hits the closed throttle plate and reverberates back toward the compressor wheel in sort of a pressure wave.....sort of like cavitation....except with a gas. The water hammer is just like what is happening when you are at 25 psi boost and you shut the throttle off....... just like the water at the house in the bathroom sink when you close the faucet in .1 sec and get that bumping sound in the piping.......it can do damage.
I don't think it is a good thing. Will it hurt the turbo? IMHO, not on the older heavy duty models....but as the sizes increase....and hence the mass flow, I think it is more important.
Water hammer only happens with with a non-compressible liquid, where the liquid can cause major damage. Air is compressible! And how do you dead head an air compressor? Everything you mention deals with a liquid, not air. Where I work we have ARC(automatic recirculation) valves so we do not dead head the pumps running liquid.
First it was just my opinion.
The concept of what is happening is similar except air vs non-compressible liquid. In both cases (water hammer and high pressure air flow through intercooler and piping) you have a pressure spike that would be much higher than the original pressure when the fluid (water or air) was flowing that travels away from the closed valve or throttle body. There are resultant forces imparted on the compressor wheel in the turbo. Is it as bad as if it were an incompressible liquid? No.... but it isn't doing it any good either.
Dead head: a situation that occurs when the pump's discharge is closed either due to a blocage in the line or an inadvertently closed valve. At this point, the pump will go to it's maximum shut-off head, the fluid will be recirculated within the pump resulting in overheating and possible damage. By definition, we are deadheading the turbo when the throttlebody closes rapidly..... we didn't turn the compressor off prior to that, it is spinning at up to 120k RPM until we let off..... then it slows down. Although this also typically is talked about with an incompressible fluid, this same principle still applies.
If you didn't have ARC's on your pumps where you work, the life of the pump would be significantly shorter.
Why are you ballbusting anyway for my opinion? The main reason I chimed in is because I know of an instance where there was a turbo compressor wheel that sustained major damage on three instances (not just once) upon the swift closing of the throttle after a burnout..... then a BOV was installed.... not one more issue. There are significant forces at work here..... they just don't necessarily show up on all street cars. The fact remains the BOV's can save a turbo in certain situations which was the original posters "question".
The reason I'm chiming in is because what you said doesn't make sense to me. I was thought you always need water to have water hammer. It occurs from the pressure spike of slamming a valve closed. Another way is when steam contacts water which then flashes and expands almost 1700 times, but it still involves water. According to what your saying then you could get water hammer every time the poppet valves close in a head of an internal combustion engine. I don't understand how you get cavitation with air and air alone. Most of what I've learnt about cavitation deals with liquid and the flashing of it when it drops below the vapour pressure for a set temperature and results in implosions. This then causes pitting on the impellers. I've had to do pump calculations to figure out net positive suction head. All I'm asking for is scientific evidence. Maybe what I know is wrong.
I will agree they do use blow off valves on very large compressors in industry. As for the turbo that was destroyed, what kind of bearings was it using and what material was the compressor built with? I believe John Craig said he has never seen compressor damage on a turbo with 360' bearings, different story with 270' bearings. My buddy's Stage II runs 7's at 180 mph and he's never toasted a turbo with the butterfly valve slamming shut.
I will agree they do use blow off valves on very large compressors in industry. As for the turbo that was destroyed, what kind of bearings was it using and what material was the compressor built with? I believe John Craig said he has never seen compressor damage on a turbo with 360' bearings, different story with 270' bearings. My buddy's Stage II runs 7's at 180 mph and he's never toasted a turbo with the butterfly valve slamming shut.
For what it's worth, my car sneezed from the factory, we referred to it as a horse sneeze, or "Spitting out the Mustang !"
I still love the sound even with the T66.
I don't want anything on my GN that makes it sound like a ricer.
And , you can prevent the closed blade "stall" by teaching your right foot a little lessen in modulation, same reason you don't need anti-lock brakes and other chic features.
Just enjoy your hotrod and drive with both feet like you are supposed to right ?
No slam, but it is like inventing the bra that totally prevents boob bounce...
I still love the sound even with the T66.
I don't want anything on my GN that makes it sound like a ricer.
And , you can prevent the closed blade "stall" by teaching your right foot a little lessen in modulation, same reason you don't need anti-lock brakes and other chic features.
Just enjoy your hotrod and drive with both feet like you are supposed to right ?
No slam, but it is like inventing the bra that totally prevents boob bounce...
It is the concept of a pressure shockwave that I suggested as my opinion. Maybe I'm way offbase. I'm not suggesting that what you know is incorrect. I only brought it up to try and help explain what I believe is happening.
I do not know what bearings were on that turbo. It was on a low 9 sec turbo V6 car.
I do not know what bearings were on that turbo. It was on a low 9 sec turbo V6 car.
A couple of things...
"Cavitation" is the phenomenon where a liquid flashes to a vapor on the trailing edge of something that is rotating within that liquid. This happens because the local pressure in those locations is very low - low enough for the liquid to turn to vapor at a relatively low temperature. For example, the bubbles that you see on the trailing edge of a propeller running in your local lake is due to cavitation. The reason us engineers care about it (yes, I'm one of those pesky mechanical engineers) is because metal tends to be erroded when those bubbles are formed. Ever take a water pump off a car and see the pock-marks in the casting and material missing from the impeller blades? That can be due to cavitation. BTW, that's one of the reasons why cooling systems are pressurized - the higher system pressure reduces cavitation in the water pump. But I digress. Unless you are spraying alky into your turbo or something, cavitation cannot happen in a turbo, since it is only moving gases (namely air).
Liquids are "assumed" to be incompressible for just about any engineering calculation that is done on the stuff we see every day. So, for the plumbers and others out there, water is assumed to be incompressible, which means its density is assumed to not change as it flows. Most people here are familiar with "water hammer" that happens when a valve is suddently closed - the momentum of the water "slams" into whatever just closed and bounces back because the water cannot compress.
Air is a somewhat different story. Believe it or not, when doing basic engineering calculations, air can be assumed to be incompressible as long as it's speed stays below about 0.3 times the speed of sound (0.3 or less Mach number). No kidding. However, this assumption only applies for simple situations like air flowing through a pipe, an orifice, etc. For complicated situations like a compressor adding energy to the air stream (and thereby compressing it), the pressure, velocity, and density of the air are all changing. So, air in this situation is a dynamic beast unlike water flowing in a pipe.
Getting back to our situation of having a turbo spooled up and slamming the throttle shut, well, the water hammer analogy doesn't really apply. However, the thought that the air has no momentum and doesn't create any pressure waves or anything doesn't apply, either. Reality is somewhere in between those two extremes.
As I posted earlier, as soon as the throttle shuts, the compressor goes into rotating stall, meaning it is aerodynamically incapable of compressing the air. For the "engineers" out there, this is similar to an aircraft wing operating at a high angle of attack and low speed - the wing can no longer produce lift, and it "stalls". During the period while the compressor is in rotating stall and slowing down, the air pressure in the uppipe is bleeding off through the IAC, cracked throttle plate, and backflow through the compressor (even though, in fact, the compressor is still spinning in the normal direction). During this time, there are certainly pressure fluctuations (surges) going on between the compressor and throttle body (watch your mechanical boost gage while your turbo is sneezing - some of those pressure surges find their way past the throttle plate and into the intake manifold, causing your gage to vibrate back-and-forth). The back flow and pressure surges are rapidly changing the direction of the load on the bearings in the turbo.
How high are these loads? Helk if I know! I'm not even sure a full computational fluid dynamics study could calculate them accurately. For a stock turbo, apparently Garrett and GM didn't think they were high enough to worry about (thus no BOV). For a car with a larger turbo (bigger compressor, more rotational momentum, and likely similar size bearings to stock), larger intercooler (more volume between the compressor and throttle body, so more air to bounce around), and higher boost levels, maybe these loads get high enough to cause bearing damage - especially if the turbo is being asked to run at the super-high RPM's to which we push them!
So, to answer the original question - do we need a BOV? See my previous post...
Good Luck,
"Cavitation" is the phenomenon where a liquid flashes to a vapor on the trailing edge of something that is rotating within that liquid. This happens because the local pressure in those locations is very low - low enough for the liquid to turn to vapor at a relatively low temperature. For example, the bubbles that you see on the trailing edge of a propeller running in your local lake is due to cavitation. The reason us engineers care about it (yes, I'm one of those pesky mechanical engineers) is because metal tends to be erroded when those bubbles are formed. Ever take a water pump off a car and see the pock-marks in the casting and material missing from the impeller blades? That can be due to cavitation. BTW, that's one of the reasons why cooling systems are pressurized - the higher system pressure reduces cavitation in the water pump. But I digress. Unless you are spraying alky into your turbo or something, cavitation cannot happen in a turbo, since it is only moving gases (namely air).
Liquids are "assumed" to be incompressible for just about any engineering calculation that is done on the stuff we see every day. So, for the plumbers and others out there, water is assumed to be incompressible, which means its density is assumed to not change as it flows. Most people here are familiar with "water hammer" that happens when a valve is suddently closed - the momentum of the water "slams" into whatever just closed and bounces back because the water cannot compress.
Air is a somewhat different story. Believe it or not, when doing basic engineering calculations, air can be assumed to be incompressible as long as it's speed stays below about 0.3 times the speed of sound (0.3 or less Mach number). No kidding. However, this assumption only applies for simple situations like air flowing through a pipe, an orifice, etc. For complicated situations like a compressor adding energy to the air stream (and thereby compressing it), the pressure, velocity, and density of the air are all changing. So, air in this situation is a dynamic beast unlike water flowing in a pipe.
Getting back to our situation of having a turbo spooled up and slamming the throttle shut, well, the water hammer analogy doesn't really apply. However, the thought that the air has no momentum and doesn't create any pressure waves or anything doesn't apply, either. Reality is somewhere in between those two extremes.
As I posted earlier, as soon as the throttle shuts, the compressor goes into rotating stall, meaning it is aerodynamically incapable of compressing the air. For the "engineers" out there, this is similar to an aircraft wing operating at a high angle of attack and low speed - the wing can no longer produce lift, and it "stalls". During the period while the compressor is in rotating stall and slowing down, the air pressure in the uppipe is bleeding off through the IAC, cracked throttle plate, and backflow through the compressor (even though, in fact, the compressor is still spinning in the normal direction). During this time, there are certainly pressure fluctuations (surges) going on between the compressor and throttle body (watch your mechanical boost gage while your turbo is sneezing - some of those pressure surges find their way past the throttle plate and into the intake manifold, causing your gage to vibrate back-and-forth). The back flow and pressure surges are rapidly changing the direction of the load on the bearings in the turbo.
How high are these loads? Helk if I know! I'm not even sure a full computational fluid dynamics study could calculate them accurately. For a stock turbo, apparently Garrett and GM didn't think they were high enough to worry about (thus no BOV). For a car with a larger turbo (bigger compressor, more rotational momentum, and likely similar size bearings to stock), larger intercooler (more volume between the compressor and throttle body, so more air to bounce around), and higher boost levels, maybe these loads get high enough to cause bearing damage - especially if the turbo is being asked to run at the super-high RPM's to which we push them!
So, to answer the original question - do we need a BOV? See my previous post...
Good Luck,
Good job Mike.....you and my brother used to work together at GT right? I could be over generalizing my analogy of cavitation, water hammer, etc, but it all has to do with waves of pressure. I was trying to paint a basic picture.....Air for all practical purposes is compressible, but it still exibits some flow similarities to water. Some wind tunnel testing is done with water...in a pool. I saw a Ford Taurus body in a big long pool at Texas Tech University back in the mid 90's......they were doing research in the water similar to what you would do in a wind tunnel. I digress.
Back on-topic.
I am not sure the turbo that I spoke of had a bearing failure.....I think it was a wheel failure....like laying the fins over in a cheap torque converter..... at least that is how I interpreted it. I don't enough about the situation to comment with more detail.
Back on-topic.
I am not sure the turbo that I spoke of had a bearing failure.....I think it was a wheel failure....like laying the fins over in a cheap torque converter..... at least that is how I interpreted it. I don't enough about the situation to comment with more detail.
Hi Blazer,
I'm guessing from your email address that your brother is Adam, right? If so, we did work together briefly at GT - I'm sure he's told you stories. Tell him I said "hi" next time you talk to him.
Air flow over a car is a good case of being able to assume that air is incompressible. The speed of the air over the car shouldn't exceed Mach 0.3 (unless it's one helk of a Taurus, right?). So, experiments can be performed with another incompressible fluid (such as water), as long as the testing is done at the same Reynolds number (rho-V-d/mu). But, that's probably getting way too complicated for this topic.
Let the debate over BOV's continue - it's been going on as long as I've been on this board.
Regards,
sscamino
Member
- Joined
- Aug 3, 2010
- Messages
- 155
I Just learned this after running TE-67 ( biggest of the small shaft) on the street,and having to get it rebuilt every other year. Everyone on the board blamed it on me and somthing I did.Only one that guy that runs TE-67 on a motorcycle told me last year that I had to run one.After he said this I saw that most of the fast street -strip drivin cars had one either on pass side header or on the up pipe. Funny how people dont give you all the info needed .I just bought PTE 6766 billitt wheel with ported inlet and a Tial 50mm BOV as backup. I dont think Ill have any problem this year.
haywire4130
Active Member
- Joined
- Sep 11, 2010
- Messages
- 664
youre absolutely right, i have one on my car, it doesnt seem to mind, but if you watch the o2 counts on your scanmaster it goes rich briefly after a sudden throttle lift because you just discharged "accounted for" air to atmosphere. i'm going to plumb mine back into my air intake after the maf which will tone down the ricey woosh as well. i experimented with one on my near-stock gn for something to do and it didn't like it at all, it would stumble and almost stall. more heavily-modified cars tolerate it better, in my experience. the reason i put it on is my car spools up violently and breaks loose quick on street tires, usually requiring you to "pedal" it a couple times to maintain traction. without the bypass (i dont like "bov" hahaha) the "sneeze" would stall the compressor and the boost would take longer to come back. with it, there just a quick venting of boost as i lift and it comes back on boost instantly. the purists on this site with real fast cars seem to hate them, but to each his own. for the original author of this post: if you decide to buy one, get a quality one like tial/turbosmart/turbonetics, steer clear of cheapie ebay garbage unless all you want is a cool noise to impress your buddies at the expense of performance!
note taken. i will check it out i running a precision 88mm turbo. and really dont wanna mess it up
haywire4130
Active Member
- Joined
- Sep 11, 2010
- Messages
- 664
ya, thats an expensive piece... i'd spend the extra cash on a nice one or adjust your technique when decelerating as mentioned above. mine is a turbosmart dual port, it's real nicely machined and seals up perfect. it came with a nice stainless fitting that i tig'd to my intercooler pipe right behing the radiator (i used this spot because i intended to eventually plumb the discharge back into the intake and it is a straight shot up from there). are you running a front-mount? i forgot to add that in my previous post, i have one and i feel the extra volume of air it and its piping holds makes the compressor stall worse than with a smaller stock location one, which makes a better case for running a bypass valve. of course this is my opinion and others may disagree-
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