BOV question..
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Joined: Apr 2001
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From: Alhambra
Blow off valve FAQ
http://www.alltrac.net/tuning/bovfaq.html
Why my friend upgraded his factory BOV on his eclipse... (confirm by someone else's page here)
http://www.jumptronix.com/2g_go_faster/Sta...lowOffValve.htm
Small info page...
http://www.mrtrally.com.au/performance/howbov.htm
http://www.alltrac.net/tuning/bovfaq.html
Why my friend upgraded his factory BOV on his eclipse... (confirm by someone else's page here)
http://www.jumptronix.com/2g_go_faster/Sta...lowOffValve.htm
Small info page...
http://www.mrtrally.com.au/performance/howbov.htm
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Joined: Jul 2001
Posts: 7,335
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From: Overland Park, KS
Jonboy and chroot....aaaaaaaaaaaoooooooohh.....nice to see we are getting...
Now, back to the subject of bypass valves, actuators, recirculating valves and blow off valves.....There is still an ongoing debate as if they work on some cars or not.
Take for example the 300ZXTT. First of all to understand the functionality and benefits of a blow off valve you have to have a complete understanding of how a turbocharger works. If you don't understand the basic mechanics of a turbocharger you can forget about trying to understand the benefits of a blow off valve. If you do understand the mechanics of a turbocharger, read on...
An Explanation of Compressor Surge:
The turbine in a turbocharger in its ideal mode is spinning at a very high rate and therefore generating lots of pressurized air that is fed into the OPEN (wide open throttle) intake manifold which translates into more power, but what happens when you take your foot off the gas when shifting between gears? The turbine in the turbo is still spinning at a high rate but now you've taken your foot off the gas and the intake manifold is CLOSED. Now the turbine spinning at a high rate and is trying to push out all this compressed air but since the manifold is closed, that compressed air has nowhere to go. What happens next is that the turbine slows down because of this pressure build-up between the compressor and the intake manifold. Since the pressurized air can't go forward into the engine it heads the wrong way back towards the turbo where it slows the turbine down (compressor surge). After you shift gears and you step on the gas again you want to have the turbine spinning fast so that its producing boost but since you took your foot off the gas and caused compressor surge, it slowed down, so you have to wait for the turbine to "spool up" (spin fast) again. This delay waiting for turbines to spool up is what causes some of the performance degradation that were trying to avoid.
The Blow off Valve was basically designed to be a way of eliminating compressor surge. Then the turbine in our turbo would have a much easier time keeping its speed up and we wouldn't get the lag in power waiting for the turbine to spool up between shifts. At that moment in time between shifts when compressor surge is slowing the turbine down we'll just poke a hole in the tube running between the turbo and the intake manifold and let all that air leak out somewhere. The turbine can keep spinning fast & we'll have lots of boost when we step on the gas again. We'll also want to plug up that hole we made because we have a purpose for that pressurized air now, where as when we let off the gas we did not. The blow off valve is a gizmo that's constantly opening and closing giving you that cool sneeze sound when it "pokes" that hole in the intake manifold tube to keep the turbine spinning fast. We've eliminated compressor surge but we did confuse the engine just a bit since the ECU already told the injectors to issue fuel to be used for the air that we've now thrown out. Other than that sounds like a good idea right? so what if were running a bit rich for a moment, no big deal.
So before you go and order one online, read on (wheew my fingers are hurting)....
The Re-circulating Valve... a better idea:
How about instead of poking a hole in the turbo to intake manifold tube and just letting the air leak out wherever it wants to, we could direct that pressurized air somewhere else where we could hold on to it until we need it again? The intake side of the compressor housing (between the intercooler and the turbo) would be a good place wouldn't it? that way we wouldn't slow the turbine down and we would have that pressurized air that would have otherwise been thrown out, ready in a really good place when we need it. On top of that eve got still got the correct air/fuel ratio going since we're not throwing and air out, just moving it from one place to another within the intake system. Instead of having to suck in air for the turbo to pressurize, we've got some pressurized air with the correct fuel amount already waiting. Now we've got all the benefits of a blow off valve and then some. That's a re-circulating valve. Let's all order re-circulating valves then and skip the blow off valves completely. They're probably gonna cost a bit more than the blow off valves since they work a little better right? Now the big surprise... Re-circulating valves were engineered into the design of the 90+ twin turbo z on the drawing board... you've already got them...
In conclusion: You could always disconnect your stock re-circulating valves (which you have to do to install blow off valves) and spend 500-600 bucks for blow off valves and what will you get? better performance? No, basically you do get the cool sneeze sound though you aren't going to be any faster than you were before (but you might sound like you are). If by chance you are running boost levels that exceed the airflow capacity of the re-circulating valves (600+ hp on a 300ZTT) then you've probably spent enough money and have enough experience and knowledge to know where the benefit reverses.
Again, this would only apply to Zeds...if you have another car, it could be completely different
Now, back to the subject of bypass valves, actuators, recirculating valves and blow off valves.....There is still an ongoing debate as if they work on some cars or not.
Take for example the 300ZXTT. First of all to understand the functionality and benefits of a blow off valve you have to have a complete understanding of how a turbocharger works. If you don't understand the basic mechanics of a turbocharger you can forget about trying to understand the benefits of a blow off valve. If you do understand the mechanics of a turbocharger, read on...
An Explanation of Compressor Surge:
The turbine in a turbocharger in its ideal mode is spinning at a very high rate and therefore generating lots of pressurized air that is fed into the OPEN (wide open throttle) intake manifold which translates into more power, but what happens when you take your foot off the gas when shifting between gears? The turbine in the turbo is still spinning at a high rate but now you've taken your foot off the gas and the intake manifold is CLOSED. Now the turbine spinning at a high rate and is trying to push out all this compressed air but since the manifold is closed, that compressed air has nowhere to go. What happens next is that the turbine slows down because of this pressure build-up between the compressor and the intake manifold. Since the pressurized air can't go forward into the engine it heads the wrong way back towards the turbo where it slows the turbine down (compressor surge). After you shift gears and you step on the gas again you want to have the turbine spinning fast so that its producing boost but since you took your foot off the gas and caused compressor surge, it slowed down, so you have to wait for the turbine to "spool up" (spin fast) again. This delay waiting for turbines to spool up is what causes some of the performance degradation that were trying to avoid.
The Blow off Valve was basically designed to be a way of eliminating compressor surge. Then the turbine in our turbo would have a much easier time keeping its speed up and we wouldn't get the lag in power waiting for the turbine to spool up between shifts. At that moment in time between shifts when compressor surge is slowing the turbine down we'll just poke a hole in the tube running between the turbo and the intake manifold and let all that air leak out somewhere. The turbine can keep spinning fast & we'll have lots of boost when we step on the gas again. We'll also want to plug up that hole we made because we have a purpose for that pressurized air now, where as when we let off the gas we did not. The blow off valve is a gizmo that's constantly opening and closing giving you that cool sneeze sound when it "pokes" that hole in the intake manifold tube to keep the turbine spinning fast. We've eliminated compressor surge but we did confuse the engine just a bit since the ECU already told the injectors to issue fuel to be used for the air that we've now thrown out. Other than that sounds like a good idea right? so what if were running a bit rich for a moment, no big deal.
So before you go and order one online, read on (wheew my fingers are hurting)....
The Re-circulating Valve... a better idea:
How about instead of poking a hole in the turbo to intake manifold tube and just letting the air leak out wherever it wants to, we could direct that pressurized air somewhere else where we could hold on to it until we need it again? The intake side of the compressor housing (between the intercooler and the turbo) would be a good place wouldn't it? that way we wouldn't slow the turbine down and we would have that pressurized air that would have otherwise been thrown out, ready in a really good place when we need it. On top of that eve got still got the correct air/fuel ratio going since we're not throwing and air out, just moving it from one place to another within the intake system. Instead of having to suck in air for the turbo to pressurize, we've got some pressurized air with the correct fuel amount already waiting. Now we've got all the benefits of a blow off valve and then some. That's a re-circulating valve. Let's all order re-circulating valves then and skip the blow off valves completely. They're probably gonna cost a bit more than the blow off valves since they work a little better right? Now the big surprise... Re-circulating valves were engineered into the design of the 90+ twin turbo z on the drawing board... you've already got them...
In conclusion: You could always disconnect your stock re-circulating valves (which you have to do to install blow off valves) and spend 500-600 bucks for blow off valves and what will you get? better performance? No, basically you do get the cool sneeze sound though you aren't going to be any faster than you were before (but you might sound like you are). If by chance you are running boost levels that exceed the airflow capacity of the re-circulating valves (600+ hp on a 300ZTT) then you've probably spent enough money and have enough experience and knowledge to know where the benefit reverses.
Again, this would only apply to Zeds...if you have another car, it could be completely different
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Joined: Jul 2001
Posts: 7,335
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From: Overland Park, KS
QUOTE]Originally posted by foolio
Hey thanks for all the info; you described it very nicely.
However, I think you meant rerouting the air back to the front of the turbo inlet, after the MAFS:
If you route the air back "between the intercooler and the turbo", you're not relieving any back pressure off the turbo are you? [/QUOTE]
jeeezhssh sweet girls in ceaser salad.....you read ALL that?
hehehe. Now you have me thinking...I am tearing up my whole system in October/November...how about if I let you know then...I think I am sticking w/my theory
Hey thanks for all the info; you described it very nicely.
However, I think you meant rerouting the air back to the front of the turbo inlet, after the MAFS:
If you route the air back "between the intercooler and the turbo", you're not relieving any back pressure off the turbo are you? [/QUOTE]
jeeezhssh sweet girls in ceaser salad.....you read ALL that?
hehehe. Now you have me thinking...I am tearing up my whole system in October/November...how about if I let you know then...I think I am sticking w/my theory
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Joined: Aug 2001
Posts: 1,607
Likes: 0
From: Santa Clara
Recirc valves put the blown-off air back in front of the turbo. The pressure is lower before the turbo, and the high-pressure blown-off air flows that way. If you routed the blown-off air after the turbo, there'd be no pressure differential, and no flow.
When the blown-off air is recirculated to the front of the turbo, it effectively makes a little closed loop of air -- little air is entering the engine (since the throttle is closed), and little new air is coming into the turbo (it's all coming from the recirc valve after the turbo). The turbo is just blowing the same air around in circles (and staying spooled at full speed) until the throttle opens up again.
- Warren
When the blown-off air is recirculated to the front of the turbo, it effectively makes a little closed loop of air -- little air is entering the engine (since the throttle is closed), and little new air is coming into the turbo (it's all coming from the recirc valve after the turbo). The turbo is just blowing the same air around in circles (and staying spooled at full speed) until the throttle opens up again.
- Warren
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Joined: May 2002
Posts: 200
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From: Colorado Springs
go to the A4 forum at www.audiworld.com and you will get a resounding no for putting a BOV on an A4. The A4's system wasn't designed to use one, and will gain you nothing.
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May 22, 2002 01:02 AM