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savedbygrace
Well-known member
Post your opinions and/or theories of operation proudly below.
Again experience may be helpful…
Junior
Again experience may be helpful…
Junior
What is the purpose of a Blow off valve(BOV)??? How does it work and why???
- Thread starter savedbygrace
- Start date
Blowoff valves are used to prevent compressor surge, which can happen when the throttle is quickly closed on a turbocharged engine. When the throttle plate on a turbocharged engine closes, the high pressure air in the intake system is trapped by the throttle and a pressure wave is forced back into the compressor. The compressor wheel slows rapidly and may even stall, the driver will notice a fluttering air sound. The rapid slowing or stalling stresses the turbo and imparts severe turbo lag/explosion if the driver accelerates immediately after the surge event, repeated surge can also lead to turbo failure.
So the BOV is not just something to install for the cool noise, IMO all turbo systems should incorporate a BOV evan at low boost pressures like 3-4 PSI, as they help extend component life and can be done for under $120.
So the BOV is not just something to install for the cool noise, IMO all turbo systems should incorporate a BOV evan at low boost pressures like 3-4 PSI, as they help extend component life and can be done for under $120.
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product tester
Well-known member
here is the biggest reason every one of my kits has a bov with out one even at 4#s at 500 miles the intake of the turbo is coated with oil a real mess witch does not affect performance , but where the performance is affected is on a long run where you get in and out of the throttle is starts to puff oil out the exaust witch means its going into the intake also witch creates loss in power and change in fueling.
A wastegate is mounted on the exhasut side before the turbine wheel. It is used to divert or bypass exhaust from the turbine wheel to keep you at a targeted user defined boost level. It starts off closed to keep max energy going through the turbine and then opens once you hit the boost level you want. There are external and internal wastegates, internal are intergrated into the turbine housing and external are able to be mounted in a variety of ways depending on the layout.
Wastegate pictures:
External:
http://store.forcedperformance.net/...ode=FP&Product_Code=TIMV-S&Category_Code=TiAL
http://store.forcedperformance.net/..._Code=FP&Product_Code=TI38&Category_Code=TiAL
02 housing and external wastegate for EVOIII turbo
http://stores.punishment-racing.com/-strse-212/Talon-fdsh-Eclipse-Tial-MVS-38mm/Detail.bok
Internal wastegate pics:
http://store.forcedperformance.net/...roduct_Code=NTEVOGreen&Category_Code=Turbo-FP
http://store.forcedperformance.net/...duct_Code=NTDSM18G6SL2&Category_Code=Turbo-FP
A BOV is mounted on the charge piping, (post intercooler if applicable) and is used to prevent compressor surge.
BOV Pics:
Stock 1g mitsu
http://www.maperformance.com/mitsubishi-1g-blow-off-valve-with-gasket.html
Aftermarket:
HKS
http://www.maperformance.com/hks-super-sqv3-sequential-blow-off-valve-hks-sqv3.html
TIAL
http://www.maperformance.com/tial-sport-q-vent-to-atmosphere-blow-off-valve.html
http://www.maperformance.com/tial-sport-alpha-q-recirculating-blow-off-valve.html
Picture showing both BOV (on left) and wastegates (center of picture near radiator)
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A wastegate "regulates" the exhaust that spins the fan inside the turbo preventing the turbo from overcharging the system......While a BOV regulates the charge between the turbo charge tube and the carberator.
Both the Wastegate & BOV are "saftey parts" that protect the system from potential damage.
OT
i know a lot of people dont run the BOV on lower boost setups, which seems sorta dumb to me, as they are relatively cheap, and help overall component life of everything else is increase as well.
the huge benefit for rideability, especially at lower boost is that your turbo can keep up a much higher spool when you chop the throttle as the air can just be moved into the atmosphere... this really helps when you are under full boost then totally let off then back on... sudden throttle chops like that and the power is back faster then say if you didnt. maybe not a huge noticable difference, but a BOV incorperated with with a well rounded setup is that you can make a MUCH more rideable setup by just adapting parts together properly. shall i say synergy?
also, the most ideal setup for a blow off valve in my mind is to have it instead of dumping air into the enviroment, is you plump it back into your turbo inlet, so the turbo is seeing air pushing into it, this way, again, you great less drag on the turbo and it can maintain a spool when you are on and off the throttle, with a setup like this you dont get the coool pshhhhh noise, BUT, you get more performance.
obviously some of these things may not be a huge seat of the pants difference, BUT, incorperating lots of them together, they can make a bit more power, and can be the difference between getting stuck of inching over the top/
the huge benefit for rideability, especially at lower boost is that your turbo can keep up a much higher spool when you chop the throttle as the air can just be moved into the atmosphere... this really helps when you are under full boost then totally let off then back on... sudden throttle chops like that and the power is back faster then say if you didnt. maybe not a huge noticable difference, but a BOV incorperated with with a well rounded setup is that you can make a MUCH more rideable setup by just adapting parts together properly. shall i say synergy?
also, the most ideal setup for a blow off valve in my mind is to have it instead of dumping air into the enviroment, is you plump it back into your turbo inlet, so the turbo is seeing air pushing into it, this way, again, you great less drag on the turbo and it can maintain a spool when you are on and off the throttle, with a setup like this you dont get the coool pshhhhh noise, BUT, you get more performance.
obviously some of these things may not be a huge seat of the pants difference, BUT, incorperating lots of them together, they can make a bit more power, and can be the difference between getting stuck of inching over the top/
The primary purpose for a BOV is to let extra air pressure out of the airbox when the throttle is closed.
A secondary purpose would be to let air into the airbox a few split seconds before the turbo can build boost and take over.
It all depends on where the BOV gets its' signal.
A secondary purpose would be to let air into the airbox a few split seconds before the turbo can build boost and take over.
It all depends on where the BOV gets its' signal.
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Jkinzer
Well-known member
thank you for that... i've always been curious why the hell my filter was always coated with oil, always figured it was just from rolling my sled and oil getting on it or something, but the no BOV thing makes a lot more sense
So everyone is explaining the same thing cool. Great answers..
I want to know why they dont use BOV's on say my 12V cummins. I am running a zero plate and when getting on it I get what I think is over boost and I get "a shudder". It sounds to me like I should put a BOV on and let it blow off the xtra boost.. However I have never heard of a BOV on a diesel setup. Any thoughts.
I want to know why they dont use BOV's on say my 12V cummins. I am running a zero plate and when getting on it I get what I think is over boost and I get "a shudder". It sounds to me like I should put a BOV on and let it blow off the xtra boost.. However I have never heard of a BOV on a diesel setup. Any thoughts.
J
JSCC
Well-known member
This guy knows whats going on! Nice response.
I was also told that you can get what they call "turbo runon" that is when you let off the throttle but the turbo is still forcing air into the air box and the sled will want to keep moving like the throttle is still on for a few feet till the boost pressure decreases. I think that happens more often on carburated snowmobiles unless you install a BOV
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Drifter
Well-known member
Well for starters Diesels dont have throttle plates. New engines like the latest Duramax are an exception. I have seen lots of High performance diesels with a BOV. 6.0L fords stock in the right situation you can get them to stall the compressor. Even stock but you have to work at it. Long story short most truck diesel truck engines dont need them.
If you are running a really big fuel plate with bigger injectors your stock turbo on a 12 valve is possibly undersized. You might want to see how much boost you are running start getting up around 35 plus you could be looking for a falure.
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POLARIS600cc
Member
No bov's standard on diesels because there is no throttle plate(s) that close. It can be done, but you have to wire in a solenoid that vents the bov's boost signal line to atmosphere at 0% throttle, and then at anything above 0% the solenoid switches to a boost reference. I'm sure you can get fancy and change it up to work at say below and above 30% or whatever you want.
Edit: Looks like me and drifter had the same idea I just took 3 minutes to long when I was typing lol.
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Yes I regularly reach 40psi boost pressure at about 1250*. There are tons of guys getting just that and tons of literature on turbo diesel registry.. The solenoid comments make sense. Not trying to start a fight or change the subject or poach the thread it just peaked my curiosity reading this thread..
So is it possible to get both of these situations out of a BOV?? both of these take different signals, just wondering if it was possible..??
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JHG
Well-known member
Car and trucks don't come stock with BOV's because they are not street legal. You can run a bypass valve and that is pretty much what skidooin'it is talking about.
I guess I'll ask another question here.....If you are running low boost, say a pump gas set up where it is designed to run on low boost, wouldn't a blow off valve contribute to the "turbo lag" that everyone is working so hard to minimize? If you depressurize the charge tube every time you let off the throttle, wouldn't it take more time to pressurize the charge tube again after you get back on the throttle?
Hold on, I have more questions. Who has ever experienced turbo damage or "turbo chatter/shutter" at lower boost levels (i.e. <9 #)? In an automotive application where most of the garret turbos are running similar boost levels, very few are running a BOV or Bypass Valve and they are running a lot more miles than the average snowmobile goes.
And the last note I have before I shut up, I doubt that the BOV is going to make the difference in whether or not you make it the last few inches over the top. If I'm worried about making it over the top, I've got the sled WFO and the BOV isn't really a player in that situation.
I guess I'll ask another question here.....If you are running low boost, say a pump gas set up where it is designed to run on low boost, wouldn't a blow off valve contribute to the "turbo lag" that everyone is working so hard to minimize? If you depressurize the charge tube every time you let off the throttle, wouldn't it take more time to pressurize the charge tube again after you get back on the throttle?
Hold on, I have more questions. Who has ever experienced turbo damage or "turbo chatter/shutter" at lower boost levels (i.e. <9 #)? In an automotive application where most of the garret turbos are running similar boost levels, very few are running a BOV or Bypass Valve and they are running a lot more miles than the average snowmobile goes.
And the last note I have before I shut up, I doubt that the BOV is going to make the difference in whether or not you make it the last few inches over the top. If I'm worried about making it over the top, I've got the sled WFO and the BOV isn't really a player in that situation.
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