Purpose of BOVs?

N

Nick56289

New Member
Oct 7, 2005
41
0
0
What exactly do they do? I know the release pressure when you let off the throttle quickly and such but are they really necessary? Can the pressure really back up and hurt your turbo like people suggest? I mean I know they sound cool but Id rather people assume im not running huge amounts of boost:). Any knowledge youd like to send my way?
 
7MGTEsup

7MGTEsup

Formerly 'Down but not out'
Jun 14, 2005
614
0
0
England
In server cases it can stall the turbo which is very bad, if you don't like the pissshhhhhhhh of a bov get a cbv like the bosh 110 that feeds it back into your inlet and is much quieter.
 
J

jester1341

topless and blown
Mar 30, 2005
319
0
16
39
Western Maryland
very very true....i wish i could find my old compressor wheel[i have it some where] and i would show you what compressor surge can do!!

*shivver*....get a BOV that recircs. it's cheap insurance

john
 
group a supra

group a supra

SPAWNING AN INTERCEPTOR
May 5, 2005
1,667
0
0
48
learning to weld :) in the united kingdom
bov's came about because under xtreme pressure in motorsport conditions many years ago it was known for the turbo shaft to snap under the pressure coming back
as for road cars over the years as always motorsport technology filters on to road cars ;)
 
americanjebus

americanjebus

Mr. Evergreen
Mar 30, 2005
1,867
0
0
37
wa.
just think about it this way, even when you let off of the gas the exhaust gasses are pusshing the wheel REALLY hard in one direction and when you let off of gas and close the throttle the compressed air trys to push on the wheel on the opposite ways.

take a metal rod less than a cm thick and put two people on each end with handles and have them try to turn it in opposite directions, sooner or later it will get stressed to the point where the metal is brittle and pop, it snaps.

u dont need massive amounts of boost, the frequency of putting stress on it is enough.
 
Dirgle

Dirgle

Conjurer of Boost
Mar 30, 2005
1,632
0
36
42
Pauma Valley, CA
Much like IJ, americanjebus, and group a implied, not having a BOV/BPV can cause compressor surge. And compressor surge at the shaft RPM that today’s turbo’s spin at can easily snap the smaller shafts and seriously damage/destroy the larger turbos.

Consider this, as you accelerate and your turbo is spinning up/entering boost. It is forcing a lot of air pressure/volume into your engine. Even more pressure/volume is coming out of your engine in the form of exhaust energy. This exits though the turbine by spinning it, at very high speeds I might add (between 80,000 and 150,000 rpm). The exhaust MUST exit therefore, the turbine MUST spin.

Now Imagine on the compressor side the turbo is at full spool the engine is screaming along at 6,500 rpm’s and you suddenly slam the throttle shut! All that air the compressor wheel was moving (and don’t kid yourself, it was moving A LOT of air!) can’t go forward anymore. So 20 PSI(or whatever you run) starts to go backward but to do this it has to go through the compressor wheel , which is still spinning forward, propelled by the turbine.

This causes the air to push against the compressor wheel, which is still being pushed forward, twisting the shaft and can cause it to snap!

However, if you have a larger shaft that won’t snap so easily, something much more destructive occurs. As the compressor continues to spin forward, driven by the turbine, the air oscillates between moving forward, and being forced backward through the compressor by the built up pressure. This occurrence is similar to a ships propeller cavitating in the water. When a propeller cavitates it can cause the entire ship to vibrate violently.

Now imagine this violent vibration happening to a perfectly balanced piece of precision machinery spinning at 100,000 RPM’s. Destruction is imminent! Resistance is futile!

How do we fix this? Simple, install a valve to bleed of the excess pressure each time the throttle is closed. Thus, the purpose of a blow off valve.

*Compressor surge at low pressure levels sounds similar to an owl hoo-ing(fluttering). Luckily I have not heard what compressor surge sounds like at higher pressure levels, and hope to never have that experience.

**Also compressor surge at LOW pressure levels does not always end in destruction. The guy I bought my car from had installed a new Bosch recirc-valve in the wrong direction. This caused compressor surge. He thought the owl hoo-ing(flutting) sound was cool so he ran around like that for three months, before I bought it. The turbo only had minor shaft play.
 
You must log in or register to reply here.
Top Bottom