Originally Posted by t24todd

ha expecting a little more info other than uh yea..i mean im trying to see why other than just yea...icemark? aaroncake? i tryed searching

Originally Posted by NCDA

Stock turbo? You can get away with not running one, but you dramatically decrease the life of the turbo.

Originally Posted by NZConvertible

Pure, unadulterated BS. The BOV does nothing to increase the stock turbo's lifespan. Nothing.

Originally Posted by 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.

Originally Posted by 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 ?.

Originally Posted by RICE RACING

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

Originally Posted by CarbonR1

BOV's are primarily in the OEM to reduce the noise from compressor surge. They are even used on diesel motors that have no throttling lose. When running without one, it theoretically the hardest on the thrust bearing/BB cartridge because when the throttle is closed, it tends to want to put an axial load on the rotating assembly towards the turbine side. This is due to the pressure being on the turbine side acting underneath the wheel to put the whole assembly in an quick axial load.

I don't think it would be possible to feel something like this from the driver's seat, because it happens so quickly. Also, it is not practical to compare DD turbo systems to racing turbocharging. For the sake of performance, reliability is often compromised. The turbos used in high racing applications are rebuilt after each race, so who would care if it was hard on the bearing system?

I'm not a fan of the BOV sound, but they are there for a reason, even if performance is a bit lower.

-Kevin

Originally Posted by Barban

A wastegate, no matter how effective, can not eliminate the necessity for a BOV. A wastegate can only relieve backpressure from the turbo, which actually exascerbates the problem inherent to a no-BOV system(front pressure).

When you let off the gas under boost the compressor will continue to spin and build boost between itself and the closed throttle body until the force of the compressed air in front of the turbo is greater than the combined force of the exhaust pressure and momentum of the spinning CHRA.

When the pressure of boost is greater than the absent exhaust pressure(thanks to the wastegate trying to replace the BOV) and the force generated by the momentum of the rotating assembly(which is a lot at 150,000rpm's) the compresser wheel and everything on the adjoining shaft will bounce off of the compressed air(instantly and violently, I might add).

Modern turbocharger and metalurgy technology has made it possible to bounce your turbo and detonate on apex seals multipe times before failure. But, I like to look at it like this:

Running a turbo car witout a BOV is like smoking cigarettes at the gas pump; you will get away with it for a while.

Originally Posted by mono4lamar

I've seen surging that has bent the compressor fins... Am I the only one?

Originally Posted by phoenix7

...can you SEE why some would have a hard time knowing what is correct info and what isn't???