I was just searching Ebay, looking at the cheap Greddy rip off BOV's, and notice that most say there adjustable in preassures, like 10- 25 PSI for instance. what does that mean? also I notice on the top there is writing that has 2 arrows and Hard and Soft written next to them, and what looks to be an adjustment in the center, what is that?[/u]
how does a blow off valve work
- Thread starter matt1967
- Start date
for the most part a BOV shouldn't go off at a set pressure. one side (the top most) to manifold vac). basicly when you lift your foot to shift or slow down the vac will cause it to open and vent boos tpresssure out to keep the compressure from overloading (think of it as an unloader valve like on an aircompressor)
a wastegate is a different story. those will open at a set pressure but you use air pressure to adjust that opening pressure.
a wastegate is a different story. those will open at a set pressure but you use air pressure to adjust that opening pressure.
pretty much.
A BOV is a simple spring loaded poppet valve. It balances pressure on the face of the poppet against the spring closing force. An adjustable BOV merely allows adjustment of the amount of spring load which closes the poppet. They tend to be somewhat imprecise and if not properly damped can be quite fragile.
With a dry flow system (EFI or blow-thru) they can be installed on either the turbine inlet or the compressor discharge. With a wet flow systen (draw thru) they must be installed on the turbine inlet.
In a dry flow system, the advantage of a compressor-discharge BOV vs. a waste gate is that it vents pressure without altering turbine speed so there is no spool-up time after the BOV resets. The disadvantage is that they do not prevent overspeeding the turbine and can lead to massive and expensive turbine damage.
A waste gate on the other hand dumps turbine inlet flow whenever compressor discharge pressure is exceeded. This slows the turbine down and protects it but adds to spool up time.
With a dry flow system (EFI or blow-thru) they can be installed on either the turbine inlet or the compressor discharge. With a wet flow systen (draw thru) they must be installed on the turbine inlet.
In a dry flow system, the advantage of a compressor-discharge BOV vs. a waste gate is that it vents pressure without altering turbine speed so there is no spool-up time after the BOV resets. The disadvantage is that they do not prevent overspeeding the turbine and can lead to massive and expensive turbine damage.
A waste gate on the other hand dumps turbine inlet flow whenever compressor discharge pressure is exceeded. This slows the turbine down and protects it but adds to spool up time.
strange ranger makes a good point. a BOV is not to replace a wastegate but to compliment it. boost should be limited by a wastegate and spool between shifts carried by a BOV. a wastegate is very important if you are running a smaller turbine housing as it will spool fast and give higher shaft speeds.
the point of most BOV (aside from the older indy cars?) is to keep a pressure wave from bouncing off your throttle plates when they close and reverting back into the compressor. this will slow the turbine down/stall it out. it can also lead to compressor damage. generally this is only a concern on high flow systems (20 pounds or more of boost or very high flow rates)
the point of most BOV (aside from the older indy cars?) is to keep a pressure wave from bouncing off your throttle plates when they close and reverting back into the compressor. this will slow the turbine down/stall it out. it can also lead to compressor damage. generally this is only a concern on high flow systems (20 pounds or more of boost or very high flow rates)
A
Anonymous
Guest
You guys are getting all mixed up!!
THIS IS TRUE FOR A BLOW-OFF VALVE:
THIS IS TRUE FOR A POP-OFF VALVE:
They aren't the same thing.....the BOV has a vacuum line attached to the top of it and releases pressure ONLY AFTER you let off of the accelerator pedal (because the throttle closes and creates vacuum in the intake manifold). The helps to prevent compressor surge, which is reverse airflow through the compressor.
Pop-off valves are what you see in all the high-hp belt driven supercharger cars that need a way to vent excess boost. You can't run a wastegate on a drive belt, and a variable speed clutch to control belt speed would cost a hallacious amount of money. So they just use a pop-off valve to vent excess pressure.
THIS IS TRUE FOR A BLOW-OFF VALVE:
turbo_fairlane_200":1g8zbiqr said:
THIS IS TRUE FOR A POP-OFF VALVE:
StrangeRanger":1g8zbiqr said:
They aren't the same thing.....the BOV has a vacuum line attached to the top of it and releases pressure ONLY AFTER you let off of the accelerator pedal (because the throttle closes and creates vacuum in the intake manifold). The helps to prevent compressor surge, which is reverse airflow through the compressor.
Pop-off valves are what you see in all the high-hp belt driven supercharger cars that need a way to vent excess boost. You can't run a wastegate on a drive belt, and a variable speed clutch to control belt speed would cost a hallacious amount of money. So they just use a pop-off valve to vent excess pressure.
how soon are you looking for one? I might be taking my ebay special one off for a 50mm TiAl BOV. I can make you a real good deal on it (not like they cost much)
what is you ebay special? a standard Greddy flange or an HKS flange? I'm looking at the intercooler piping that has BOV flanges welded on, there's 1 that is like 23" long, has a 90* bend in it and has an HKS flange on it. the others are small 6" sections with a BOV flange, some with the , you can get them with or without the BOV, but they use the standard greddy BOV'sturbo_fairlane_200":2wyqx92g said:
greddy flange. I will toss in the pipe I have it mounted on too.
Similar threads
