Couple Questions - BOV
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Evolving Member
Joined: Feb 2004
Posts: 105
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From: Northern NJ
Originally Posted by Fluid1
EVO-lust.
If you have a serious question, and have tried to find the information, then ask it, and I'll help you search.
I thought I made this equally clear in my second post in this thread. If you ask a well thoguht out question, everyone would love to help. If you ask what a BOV is when in fact your car comes stock with a DV, then you should start by reading your owner's manual.
If you have a serious question, and have tried to find the information, then ask it, and I'll help you search.
I thought I made this equally clear in my second post in this thread. If you ask a well thoguht out question, everyone would love to help. If you ask what a BOV is when in fact your car comes stock with a DV, then you should start by reading your owner's manual.
I didn't ask what a BOV was... I didn't ask what it does... I asked WHY people here are installing new ones.
....whatever... forget it...
There's a lot of stipulation between what people call a BOV and a diverter valve. Evo's come stock with a diverter valve. But it's also called a BOV. In all actuality they are pretty much the same thing accept for the fact that one blows the air out into the atmosphere, and the other recirculates the air back into the intake. They even make BOV's that you can choose to vent to atmosphere or recirc. And there are BOV's that can do both at the same time. So in true definition, the Evo comes stock with a diverter valve.
People install new ones for numerous reasons. A leaking stock BOV because of high boost pressures, a different sound, or for the look of something extra under the hood are all reasons that people change out their stock BOV.
People install new ones for numerous reasons. A leaking stock BOV because of high boost pressures, a different sound, or for the look of something extra under the hood are all reasons that people change out their stock BOV.
"People" are isntalling new ones so they can hold more boost without it leaking through the crappy plastic stock DV. When you get a new DV or BOV make sure you keep it installed in the same configuration as the stocker. As warrtalon said, the stocker will leak at about 13psi, which you can imagine, makes efficiency in the system, well, inefficient. The JDM MR DV and the Forge RS DV will be your best choice, as they are made to hold just about all the boost we can, or will throw at it, rather. Good luck! Hope we helped.
Thread Starter
Evolving Member
Joined: Feb 2004
Posts: 105
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From: Northern NJ
Originally Posted by occultworks
Hey, his searching methods may be flawed, that's okay. So yeah, he didn't know it had a DV, which is quite basic. But he does now, and maybe he'll be able to find more answers than he did before. I think his question was why people put aftermarket DVs and BOVs on this car. Even if he didn't know it came with a DV, that's still a legitimate question, I guess. I think he was just confused because he had seen more than one explination and the reason for DVs and BOVs. I think reading that a BOV was to prevent too much pressure from building up in the combustion chambers would throw me off too, when in fact it is to prevent compressor surge and damage to the turbo. Anyway...
Here is a quote from something I read earlier that might have confused me. I was asking why people install BOV's because I thought what the EVO had was a "wastegate". Is that such a crime? I guess my big mistake was that I looked around on the interenet to find information because... frankly... the information I got from this amazing "search button" you all praise and sing about was 90% crap. And I also read threads that seemed to contradict eachother.
Originally Posted by some dude
The blow-off valve should not be confused with a waste-gate. The waste-gate is a
device that by-passes the turbine wheel of the turbocharger, limiting the
shaft-speed of the turbocharger. Therefore, limiting the boost
(pressure) that the compressor generates and keeping the turbocharger
from over-speeding.
A blow-off valve is mounted in the intake plumbing between the
turbocharger compressor and the throttle plate. The blow-off valve is a
second safety measure against the turbocharger over-boosting and damaging
the engine.
The blow-off valve is more commonly used to keep the turbocharger spinning
when the throttle plate is suddenly closed. When the turbocharger is
generating maximum boost pressure at full throttle and then the throttle
is suddenly closed, compressed air coming from the compressor slams
against the throttle, generating extremely high pressures that travel
backwards to the compressor stopping the compressor from spinning. When
the throttle plate is again opened, the engine must spool the turbocharger
shaft again. The effects of this high pressure can also be very damaging
to the turbocharger.
device that by-passes the turbine wheel of the turbocharger, limiting the
shaft-speed of the turbocharger. Therefore, limiting the boost
(pressure) that the compressor generates and keeping the turbocharger
from over-speeding.
A blow-off valve is mounted in the intake plumbing between the
turbocharger compressor and the throttle plate. The blow-off valve is a
second safety measure against the turbocharger over-boosting and damaging
the engine.
The blow-off valve is more commonly used to keep the turbocharger spinning
when the throttle plate is suddenly closed. When the turbocharger is
generating maximum boost pressure at full throttle and then the throttle
is suddenly closed, compressed air coming from the compressor slams
against the throttle, generating extremely high pressures that travel
backwards to the compressor stopping the compressor from spinning. When
the throttle plate is again opened, the engine must spool the turbocharger
shaft again. The effects of this high pressure can also be very damaging
to the turbocharger.
Thread Starter
Evolving Member
Joined: Feb 2004
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From: Northern NJ
Ok... thanks to those that answered my questions. It's just annoying that I had to spend more time defending myself than getting information. Next time I guess I just wont bother.
Originally Posted by EVO-Lust-VIII
Ok... thanks to those that answered my questions. It's just annoying that I had to spend more time defending myself than getting information. Next time I guess I just wont bother.
And it's real sad that someone "new" to the site has this opinion. I, at one time, didn't know much about turbo cars, BOV's, and waste gates myself. Fortunately I had my questions answered elsewhere before ever joining evoM. You almost have to watch the forums for a few months and see what to, and what not to ask.
Ahh, see that's where you got confused. BOVs/DVs are completely different from wastegates, and have 2 different functions. Like the quote says, the wastegate basically helps to control boost levels, while BOVs realease pressure in off-throttle situations to prevent compressor surge, which can damage the turbo.
Am I understanding the situation correctly now? I think you were trying to ask about blow off valves, but instead asked about wastegates, and that threw you off, yes?
Am I understanding the situation correctly now? I think you were trying to ask about blow off valves, but instead asked about wastegates, and that threw you off, yes?
Originally Posted by occultworks
Ahh, see that's where you got confused. BOVs/DVs are completely different from wastegates, and have 2 different functions. Like the quote says, the wastegate basically helps to control boost levels, while BOVs realease pressure in off-throttle situations to prevent compressor surge, which can damage the turbo.
Am I understanding the situation correctly now? I think you were trying to ask about blow off valves, but instead asked about wastegates, and that threw you off, yes?
Am I understanding the situation correctly now? I think you were trying to ask about blow off valves, but instead asked about wastegates, and that threw you off, yes?
He was asking the difference between waste gates, BOV's and Diverter valves in a nut shell. and why do we add aftermarket BOV's.
Yeah, and don't let the flame wars get you down. For the most part they are correct in saying that you should always search before asking basic questions. The flames were unwarrented of course, but that was the point that was trying to be conveyed. Now we have a 5 page thread added to the millions of other threads explaining BOVs. Which makes it difficult for people like yourself to search for the answers. Try the advanced search function, that will help narrow down the sea of worthless information.
Originally Posted by Warrtalon
Evo-Lust, the big point that you're missing is that every Evo has a BOV. If we didn't have one while pushing 19-20psi, we'd absolutely destroy the compressor wheel. Half of what you said was correct - the part about when the throttle plate closes, the built-up pressure must escape somewhere, else it goes back to the compressor causing it to spin backwards. The resulting effect is called compressor surge, and it can be very damaging. With a proper BOV, we purge this additional pressure back into the intake.
Key point that may help you understand here. Technically, our Evos don't have a BOV, but rather a Diverter Valve (DV) or Compressor Bypass Valve (CBV). The second name there should ring a bell after the above explanation about compressor surge. Our stock DV recirculates the pressure back into the MAF pipe, which is the section of hose between the intake (MAF) and turbo inlet (compressor housing). A real Blow-Off Valve (BOV) is one that vents the air to atmosphere. This is a bad thing on the Evo, because it has a Mass-Air Flow (MAF) sensor that meters the air as it crosses. If this air is vented to atmosphere, then the engine supplies the wrong amount of fuel for the metered amount of air. We are not supposed to use true VTA BOVs until we have a system that bypasses the MAF - something like a speed density system using Manifold Absolute Pressure (MAP) with a standalone EMS.
So, basically, with your VIII, you have a total POS plastic DV that works fine when stock, but when raising the boost, you need to replace it. The key is to get a fully-recirculating DV like the Forge RS (fully-adjustable and holds up to 38-40psi) or the JDM MR DV (non-adjustable and holds to 24-25psi). I've used both with great success and highly recommend both, depending on your application.
Key point that may help you understand here. Technically, our Evos don't have a BOV, but rather a Diverter Valve (DV) or Compressor Bypass Valve (CBV). The second name there should ring a bell after the above explanation about compressor surge. Our stock DV recirculates the pressure back into the MAF pipe, which is the section of hose between the intake (MAF) and turbo inlet (compressor housing). A real Blow-Off Valve (BOV) is one that vents the air to atmosphere. This is a bad thing on the Evo, because it has a Mass-Air Flow (MAF) sensor that meters the air as it crosses. If this air is vented to atmosphere, then the engine supplies the wrong amount of fuel for the metered amount of air. We are not supposed to use true VTA BOVs until we have a system that bypasses the MAF - something like a speed density system using Manifold Absolute Pressure (MAP) with a standalone EMS.
So, basically, with your VIII, you have a total POS plastic DV that works fine when stock, but when raising the boost, you need to replace it. The key is to get a fully-recirculating DV like the Forge RS (fully-adjustable and holds up to 38-40psi) or the JDM MR DV (non-adjustable and holds to 24-25psi). I've used both with great success and highly recommend both, depending on your application.
Last edited by karlzhot; Apr 2, 2006 at 07:08 AM.
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