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They serve, roughly, the same purpose.

A Wastegate reduces boost being produced by allowing air to bypass the turbine.

A Blow off valve reduces the amount of compression applied to the intake air by bleeding off some of the pressure back into the intake pre-compressor. I believe they're also called by-pass valves, but I honestly can't answer that becuase I'm not sure what they are. If they are the same, then its just whatever you first heard it as or who you hang out with.

So when I said they serve roughly the same purpose, I am meaning that they are both used to control the boost going into the engine.
 

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Aren't they really the same thing? Why the different terms?
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Damn, Sleeper beat me to it, but more eloquentely.

Here is a pic:

Damn, pic pic problem, look below.

The wastegate controls the flow of exhaust gases of the turbo side. Opposite sides of the turbo.

You could check the Sticky
 

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BOV and bypass valve are the same release air after throttle plate is closed to eliminate compressor surge(bad).

Wastegate controls boost.
 

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A BOV usualy vents the compressed air to the atmosphere causing that sound every ricer (including myself) loves.

A BPV is like a BOV in every way except it vents the compressed air back into the intake before the turbo to make your car happy and is much more quiet then a BOV.
 

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A BOV usualy vents the compressed air to the atmosphere causing that sound every ricer (including myself) loves.

A BPV is like a BOV in every way except it vents the compressed air back into the intake before the turbo to make your car happy and is much more quiet then a BOV.
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BOVs can be vented back to the turbo like the BPV (recirculated mode). This has been recommended by CP-E with their HKS BOV kit. Believe me, with a CAI, you can hear the OE BPV. Most owners changed their BPV for sound and better reliability than the OE plastic BPV.
 

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To reiterate most of what's been said, and add a few comments of my own:

The wastegate allows the exhaust gas to bypass the turbine section of the turbocharger. This is how the boost level is controlled; once the boost pressure reaches the target value, the wastegate opens to prevent building more boost.

A blow-off valve operates on the intake side. When the throttle closes (like during a up-shift), the compressor is still pumping air for a short time, which now has nowhere to go. The intake pressure will rapidly spike, and the pressure valve opens to release this pressure spike. If the compressed air is vented to the atomosphere, the valve is usually referred to as a BOV. If the air is re-routed back into the intake (before the compressor), then the valve is usually referred to as a bypass valve or diverter valve.

The MS6 re-circulates the compressed air back to the intake in stock form, and most people recommend that this function be retained with aftermarket blow-off/bypass valves. The ECU is tuned to take into account the re-circulated air, so venting to atmosphere can screw with the air/fuel ratio.
 

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To reiterate most of whats been said, and add a few comments of my own:

The wastegate allows the exhaust gas to bypass the turbine section of the turbocharger. This is how the boost level is controlled; once the boost pressure reaches the target value, the wastegate opens to prevent building more boost.

A blow-off valve operates on the intake side. When the throttle closes (like during a up-shift), the compressor is still pumping air for a short time, which now has nowhere to go. The intake pressure will rapidly spike, and the pressure valve opens to release this pressure spike. If the compressed air is vented to the atomosphere, the valve is usually referred to as a BOV. If the air is re-routed back into the intake (before the compressor), then the valve is usually referred to as a bypass valve or diverter valve.

The MS6 re-circulates the compressed air back to the intake in stock form, and most people recommend that this function be retained with aftermarket blow-off/bypass valves. The ECU is tuned to take into account the re-circulated air, so venting to atmosphere can screw with the air/fuel ratio.
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Bingo, couldn't have said it any better. Nice
 

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Nice job. I may also add that I have never seen a stock car come with a BOV vented to atmosphere.
 

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To reiterate most of what's been said, and add a few comments of my own:

The wastegate allows the exhaust gas to bypass the turbine section of the turbocharger. This is how the boost level is controlled; once the boost pressure reaches the target value, the wastegate opens to prevent building more boost.

A blow-off valve operates on the intake side. When the throttle closes (like during a up-shift), the compressor is still pumping air for a short time, which now has nowhere to go. The intake pressure will rapidly spike, and the pressure valve opens to release this pressure spike. If the compressed air is vented to the atomosphere, the valve is usually referred to as a BOV. If the air is re-routed back into the intake (before the compressor), then the valve is usually referred to as a bypass valve or diverter valve.

The MS6 re-circulates the compressed air back to the intake in stock form, and most people recommend that this function be retained with aftermarket blow-off/bypass valves. The ECU is tuned to take into account the re-circulated air, so venting to atmosphere can screw with the air/fuel ratio.
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One thing to add. Maybe you meant this and just worded it differently but the air that is recirculated has already been metered by the ECU. The reason why it is "usually" bad to go from a recirculating BOV to venting to atmosphere is because when venting, you are releasing air that the ECU has already compensated for. This means when shifting/ letting off the gas, the ECU still thinks there is X amount of air, however it is no longer there. So, the car runs very very rich because the ECU is adding fuel for air that is now no longer there.

Watdog: I may also add that some turbocharged cars did not come with BOV/ BPV's such as the 300ZX TT.
 

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They serve, roughly, the same purpose.

A Wastegate reduces boost being produced by allowing air to bypass the turbine.

A Blow off valve reduces the amount of compression applied to the intake air by bleeding off some of the pressure back into the intake pre-compressor. I believe they're also called by-pass valves, but I honestly can't answer that becuase I'm not sure what they are. If they are the same, then its just whatever you first heard it as or who you hang out with.

So when I said they serve roughly the same purpose, I am meaning that they are both used to control the boost going into the engine.
Actually this is not entirely correct.

A bypass valve draws air from after the impeller but before the cylinder heads. It is then re-routed back to before the impeller and fed though the turbo again. This can be used to regulate turbo speed.

A waste gate allows the exhaust gasses to bypass the exhaust side of the turbo to slow the turbo when stopping or maintain the turbo at maximum turbo rpm. This feeds the exhaust back into the main exhaust system but bypasses the turbine.

A blowoff valve (BOV) is a solenoid pressure relief valve on the intake portion of the turbo. This valve releases the air pressure between the intake and the cylinder heads. This is important to prevent turbo surge, which occurs when a dramatic change in turbo pressure and turbo rpm takes place. This valve releases the air into the atmosphere, and is not fed back into the turbo.
 

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Please refrain from necro-bumping 10 year old posts to bicker about trivial details.
 
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