RICE RACING

Personally I LOVE the sound of the high pitched WG, it sends shiver down your spine, and you know a hard core car when you hear it

I was using a BOV before but will bypass it on my new turbo as I don't want to risk over reving the turbo while running high boost (due to WG leakage or failure), that and I want it to sound like an S2 rally Audi Quattro when I change gear or lift off the gas !!!

sbertolone

i think its cause all those cars have wastegates big enough to vent nearly all the exhaust gas so when the compressor surges it just spins the turbo backwards and it not having the exhaust push it one way and the air push it the other. just my take on it.

Marcel Burkett

I have been in the energy industry down here for the last 12 years and every one of the large compressors in use on these plants has an ANTISURGE system which does exactly what the BOV does ,ie. once the discharge flow falls below the surge limit of the compressor a controller will automatically open a valve and recycle the discharge flow back to the suction there by maintaining a minimum flow through the machine ( the BOV will vent to atmosphere which is the turbos suction ) , I have also been close to these guys when these valves / controllers fail to operate , trust me it will scare the **** out of you , it shakes very large steel structures like they were made of sticks and they also make awful loud groulig , shrieking freightening sounds.
When these machines are taken apart for maintenance you can see a lot of internal damage due to surging requiring a change out of all the related parts.
In my book physics is physics weather it is on a large or small scale , the same thing would occur , as Max explained , there would be a "violent" reversal in flow once the throttle is closed which would surely over load and eventually cause damage to the turbo , on the NISSAN RB20 engines that use the ceramic turbine wheels (we have those engines in abundance here ) the turbine wheels are often severed by this as the compressor wheel is being forced to spin opposite to the turbine when there is no BOV and nowhere for the compressed air to go , but backward , when the throttle is closed.
As we say down here it is better to be safe than sorry ,a BOV is cheap compared to replacing or repairing a large single , and also that thing about the valve failing and causing the turbo to over rev. , wouldnt you hear the air escaping ? , and most good quality valves use a diaphragm made of similar material to the waste gates' diaphragm , so what ,one shouldnt usea WG for fear of failure ?.

machinehead

Marcel, those are good points. I am just repeating what was told to me from a "very" reputable source in the turbo industry. You would think you could hear a BOV leaking but some of these cars are very loud, including mine and I am not so sure I could hear it if it were leaking. Basically I am just repeating what was told to me and it seem there may be some evidence to support this. Also, its not really the same as running without a wastgate. The wastegate is there to protect the engine from the turbo overboosting, the BOV is to protect the turbo. Also if it is so important, why don't Turbonetics, Innovative, etc., make a BOV? They have to warranty the product when it fails, wouldn't you think they would mandate the use of something so critical to turbo life?

RICE RACING

Exactly machinehead.

If it were %100 required OE turbo suppliers would "mandate" BOV's......... The only people who seem go on so much about them either sell them or supply them as an add on sale.

Still to be convinced as to why it is "bad" if anything BOV leakage or complete failure is a far bigger risk than the "potential damage" it may prevent. I think there is a bloody good reason why NO race cars ever ran them till the mandatory enforcement of POP OFF Valves, still try to figure put why they were not used in the "peak" of motorsport back in the day if they were to offer such a avenue of decreased lag and increase turbo reliability. the more I look at the function of a BOV the more it looks like a gimik. I will do more back to back tests when I finish the install of my new turbo.

maxcooper

I am not using this as iron-clad evidence of their necessity, but why do many/most cars that come with turbos from the factory have a BOV (or ABV)? It seems like they would be eliminated for cost reasons if they didn't have some benefit. Anyone care to speculate?

-Max

Marcel Burkett

I have owned five tubocharged cars , and the were all equiped with factory installed BOV's ( I make it a point to purchace "untouched " cars ).
As for race cars ....... remember its a race and engine RPM , and hence throttle opening is expected to be in the upper ranges allowing a very high flow of air through the engine / turbo for maybe the entire race .The minimum FORWARD flow through the turbo would then be satisfied thereby keeping the turbo safely away from the SURGE LIMIT.,so I guess the fitting of a BOV isn't warrented here , but on a road going vehicle , we all know what happens with traffic , putholes, pedestrians ,cops, pets etc forcing us to come off the gas and to have to mash the clutch and brake pedals.

Marcel Burkett

Also as you said MACHINEHEAD the waste gate is there to protect the engine from being over boosted , but what do you think would happen if the engine doesn't blow but manages to take the boost during a WG failure ( say maybe the turbo is a bit small or the turbine configuration allows it to peak early ) ? , again from my work experience there is also an OVERSPEED limit , these turbos already have to spin hell hard to make the boost we all love , if allowed to go uncontrolled they will eventually overspeed and disintegrate themselves due to excessive axial and radial vibrations (harmonics)sometimes causing engine damage to result from all the fragments that are eventually ingested by the engine and / or over boost.

Marcel Burkett

Actually yes I know TURBONETICS supplies bypass / blow off valves , page 52 in the 2002 catalog .
What I was trying to say about the BOV's failing is that like a WG they can fail in one of two ways , rupturing of the diaphragm or sticking of the valve , if this guy said the turbo can over rev . then he is talking about the BOV staying open , all I am saying is that this type of failure is , as I stated before , common to WG's also so does this mean we should eliminate them too? , No I definately dont think so the both have their uses in a well designed system .
Look at all of the high performance turbo cars , the evolutions , pulsars ,wrx ,supra ,RX7, 323 familia turbo, to name a few , the are all fitted withBOV's at the factory .
To avoid anything like that happening I would simply observe my boost gauge , if th BOV is open thre wouldn't be any boost , I recently posted saying that my T70 had screw up , guess what , thats exactly how I knew ...... no boost at 5000RPM and engine power was down , a problem live an open BOV will definately be spotted long before turbo overspeed failure

Snook

iTrader: (12)

very good thread guys this should be a sticky

thanks for all of the wonderful info

my opinion is run a very good blow off valve just in case and test it to make sure it isn't leaking to overspin the turbo. Take a hose at the end of it and run it into the car temporarily and check it out at all rpm ranges and boost and load

x X CLoud X x

best performance is no bov....

teamstealth

I can see a BOV being beneficial at the throttle body for absolute peace of mind. Simply because its at the primary point that pressure builds, and by releasing it, the turbo will NEVER see that pressure. By running just a wastegate, which probably is more than ok, that pressure has to travel all the way back to the turbo before it is vented, and once the pressure falls below a certain PSI (aka whatever the spring is set for), the WG closes, and that could be a problem if that pressure is more than the exhaust gases, (for instance just popping the clutch and letting the car go to idle after a hard run) ,causing the turbo to still surge. So I would still run a BOV for turbo safety, and a WG for engine safety.

-Zach

Snook

iTrader: (12)

but wont the surge make the compressor wheel spin in the opposite direction lowering boost and then it will have to work again to build the boost it just lost? Lag between shifts baby thats a bad thing. Im getting surge and i watch the graphs on the commander when I shift VERY fast it drops down to 0 psi no matter what...on my last car when i had the twins and didnt get surge it would go from 12psi to 7psi during shifts and then back to 12 SO fast. But then why does my car go to 0 psi during shifts...if the bov is releasing all the air then why is it surging hmmmmm

SM

yallgotboost

the reason it go's to 0 is cuzz the bov is letting go all the boost. I dont run a bov on my rx7. The few times its run i havent had a prob. I feel you should hook the waste gate to the ic piping and dump all the exhaust gases when you let off. Your motor can build up exhaust presure faster then boost when you shift its not goin to be in surge for very long. whats the average shift take 1/4 a sec

twokrx7

iTrader: (1)

Sorry for chiming in late but I had ignored this thread previously. The reason for the blow off valve is to increase life of the turbo, pure and simple. Is this measurable in terms of our high dollar single turbos, who knows? Seems some OEMs believe it helps their mass produced vehicle turbos, anyone know if the diesel big rigs run blow off valves?

Technical soapbox: There is a pressure pulse that travels back from the throttle plates when they go shut and no our pressure gages and MAP sensors will not be able to measure it, here's why. The pressure wave is traveling at the spead of sound, way too fast for our gages/MAP sensors to pick up. The blow-off valve is there to attempt to stop the wave from hitting the turbo compressor thus shock loading the thrust bearings and causing momentary surge, bad for the turbo no doubt but how bad? I suspect the wave will continue to bounce back and forth between the throttle and turbo a few times but it must dissipate like crazy when it hits the turbo, not sure about how many times the turbo sees a significant pressure wave.

yallgotboost

a diesel has no TB so no they do not run bov or waste gates engine rpm is controled by how much fuel is injected in now some small turbo diesel have a waste gate but there are not many of them

Romulus

I was going to add.. very few people in the buick crowd believe in them. I didn't until I got thinking about how much torque is put on the turbo shaft when I lift suddenly. Got a Tial on there now. I am having odd issues with boost spiking right when I step on the gas.. it will spike and then settle down a few psi If this continues to be a problem, I may sell it and live without one. Afterall, guys have been doing it for a looong time without turbo failure

Piranha

Ok... how are you guys that stating the wastegate will bleed off pressure measuring these effects, if at all? AFAIK, as soon as you close the throttle there isn't too much air in the exhaust manifold anyway, and I think it will bleed off WAY faster than the intake side, since you have an exhaust on the other side of the turbine, versus a compressor pushing and a throttle plate stopping.

XSTransAm

I have skimmed over this thread and maybe i misread a couple of posts, but it seems somone thinks that a wastegate is going to bleed off the boost when your throttle closes

It would open and let the remaining exhaust air pass through, and the turbo will slow down because it is no longer being spun by the exhaust gas. However this will not be enough to stop the turbo (which is spinning at 150,000+ rpms) so that the 10+psi that is between the compresser and throttle body can escape between the compressor blades. This will result in the compressed air backing up against the turbo making it surge. Just like if you were to use a turbo that was not correctly picked for the car. (turbo makes more boost quicker than the car can consume it)

This is bad for the turbo and will shorten its life significantly.

The best performance is a recirculating valve, (like in the stock system) this allows for the boost to be bled off while letting the turbo continue to spin, and not losing the energy of the air all together.

Ok so your BOV leaks at high boost, first you need to make sure its leaking, Then you need to get a BOV that WONT leak at the boost level your running.

If im not wrong a buick turbo has secondary butterflys that can be blown open with boost, That and i dont think they are running near as much psi as most turbocharged cars.

RICE RACING every car that is currently produced today (that i know of) that has a turbo incorporates a recirculating valve "bov" Im sure this isnt a joke they are playing on people

One less thing to fail??? If it fails the worst thing it could do to your car is not open, If this happens you will compressor surge and get the desired effects you seem to want anyways, and If it fails the manufacturer should replace it anyways.

I could type for hours on this, but I think here is an ok stopping point.

Oh and serious drag racers dont use them cause they never let close the throttle, If they do then they arent that serious.

RotaryRevn

ROFL

$150FC

the reason they didn't use them back in the day (IE the BMW turbo engines, etc) is because they left-foot-braked while still keeping the throttle somewhat open, and because you could replace the turbo after every race so it didn't matter.

nyt

iTrader: (1)

compressor surge stresses your thrust washer... i wouldjnt **** around w/ it