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I just was wondering why you never see a bov on a diesel? Besides the noise that i'm sure most people don't like (I happen to like thats why i'm asking) are they just not needed, does the wastegate just take care of that issue??? anybody have any info on this
 

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^^

You can install one but it wont do anything... a BOV lets the pressure between the turbo and the throttle plate bleed off when you close the throttle... otherwise it would stall or slow the turbo rapidly which can cause failure...

Anyways... you can put one in but it wont do anything on a diesel due to not having a throttle plate or any control over airflow...

-Chris
 

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sorry to burst ur guy's bubble, but they can be found on high performace diesels, with lots of air. they help limit surge. it would be something used in conjunction with a wastegate, but like i said, only in high performace applications!
the problem with them is, if it is used instead of a wastegate to control boost it can overspeed a turbocharger. as soon as it dumps the trubo boost drops off but the shaft speed goes up because of the reduced amount of work to push the air. again...not the best idea
 

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The nissan terrano runs an over boost valve (aka blow of valve sorta) from factory its the 4 cylinder version of the td42
I was checking it out yesterday while helping a mate do some tunning it was nothing but trouble so we deleted it.
 

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There are a few newer diesel engines out there with throttle plate that are used as part of the emissions control system. The 4.5L duramax that never went into production was designed with one.
 

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A bov actually is a good idea on any turbo engine. Just because there's no throttle plate doesn't mean that the turbo doesn't get hurt going from 30psi to zero instantly. Ever heard of turbo bark? Its not tough to bark a turbo on any newer diesel. Just mash the pedal til you start hauling ass then completley let off. You'll hear several short bursts of air, that's turbo bark. The boost in the cac and intake tubes takes the easiest route to atmosphere which is right through the compressor wheel.

The reason there aren't bov's on diesels is because it's almost impossible to correctly trigger them. On a gas burner, when the throttle plate closes, you trip the bov. Can't do that on a diesel. BD Diesel sells a bov kit for diesels, at least for the dmax anyway, but its $6xx! Lots of electronics to make it work properly.

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A bov actually is a good idea on any turbo engine. Just because there's no throttle plate doesn't mean that the turbo doesn't get hurt going from 30psi to zero instantly. Ever heard of turbo bark? Its not tough to bark a turbo on any newer diesel. Just mash the pedal til you start hauling ass then completley let off. You'll hear several short bursts of air, that's turbo bark. The boost in the cac and intake tubes takes the easiest route to atmosphere which is right through the compressor wheel.

The reason there aren't bov's on diesels is because it's almost impossible to correctly trigger them. On a gas burner, when the throttle plate closes, you trip the bov. Can't do that on a diesel. BD Diesel sells a bov kit for diesels, at least for the dmax anyway, but its $6xx! Lots of electronics to make it work properly.

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Turbo bark isn't a huge problem, the engine on the other end is still consuming air and it's not until the turbo slows beyond the surge point for that pressure that the air can blow back through. It's nothing like slamming a throttle plate shut on a petrol. Some modern engines use the EGR valve to vent intake pressure to the exhaust with a rapid dumping of load, probably more for consumer perception than turbo life.
 

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The other issue, as I understand it, is that diesels can run a ton of boost and will only make power for fuel they have. So the max amount of fuel is what dictates if there is too much air. There aren't the issues with lean/rich pinging etc that can affect gas engines...
 

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There are a few newer diesel engines out there with throttle plate that are used as part of the emissions control system. The 4.5L duramax that never went into production was designed with one.
since some gasser engines are coming without the throttle plate (such as the multiair from fiat or some bmw engines with the valvetronic system), it ends up quite strange to see a diesel with a throttle plate as part of the emissions control system...
 

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Turbo bark isn't a huge problem, the engine on the other end is still consuming air and it's not until the turbo slows beyond the surge point for that pressure that the air can blow back through. It's nothing like slamming a throttle plate shut on a petrol. Some modern engines use the EGR valve to vent intake pressure to the exhaust with a rapid dumping of load, probably more for consumer perception than turbo life.
This is true and false I guess. On a 100% stock motor, you probably won't bark the turbo. On a modified motor? Its easy. Heck even my 12 valve with manual tranny and just the fuel plate slid forward, and wastegate set for 30psi I can bark the turbo hard between every gear. My dmax will hit 38 psi on my hottest tune and if I chop the throttle it'll bark hard too. Stock tune on the dmax makes 30psi and will bark too sometimes. Almost any diesel with a manual tranny is very susceptible to it. The bigger the cac and intake tubing system, the more compressed air the system holds and the more likely it is to have turbo bark.

When you cut fuel the loss of drive pressure is instant, turbo bark happenes so fast that there isn't time for the engine to consume the rest of the boost in the intake tract.


I wont argue that you don't see a ton of turbo failures (ie broken shafts) from it. But I guarantee that its a big factor in bearing wear and seals that go bad.

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Some of the newest heavy duty diesels use BOV's to help with emissions and throttle response. Volvo D11D's in the 2012 model trucks have them. It vents boost pressure back into the air intake going into the turbo. They don't call it a BOV of course. Can't remember the name right now.
 

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This is true and false I guess. On a 100% stock motor, you probably won't bark the turbo. On a modified motor? Its easy. Heck even my 12 valve with manual tranny and just the fuel plate slid forward, and wastegate set for 30psi I can bark the turbo hard between every gear. My dmax will hit 38 psi on my hottest tune and if I chop the throttle it'll bark hard too. Stock tune on the dmax makes 30psi and will bark too sometimes. Almost any diesel with a manual tranny is very susceptible to it. The bigger the cac and intake tubing system, the more compressed air the system holds and the more likely it is to have turbo bark.

When you cut fuel the loss of drive pressure is instant, turbo bark happenes so fast that there isn't time for the engine to consume the rest of the boost in the intake tract.
Just thinking out loud and blue skying, without concerns for possible side issues, but what would happen if the BOV output is dumped directly into the exhaust manifold ahead of the turbine? (restoring (partial?) drive pressure). If this is patentable, I get at least 10%.
 

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Just thinking out loud and blue skying, without concerns for possible side issues, but what would happen if the BOV output is dumped directly into the exhaust manifold ahead of the turbine? (restoring (partial?) drive pressure). If this is patentable, I get at least 10%.
Already done. Car makers are using the EGR valve to dump pressure from intake to exhaust.
 

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EGR dumps exhaust into the intake, not the other way around. It uses the burnt exhaust gas as an "inert gas" to reduce the volume of fuel and air at partial throttle to effectively reduce the displacement of the engine.
 

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EGR dumps exhaust into the intake, not the other way around. It uses the burnt exhaust gas as an "inert gas" to reduce the volume of fuel and air at partial throttle to effectively reduce the displacement of the engine.
Think about this a little harder. Which pressure is higher when engine load has just been dumped? Exhaust or intake?
 

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Some of the newest heavy duty diesels use BOV's to help with emissions and throttle response. Volvo D11D's in the 2012 model trucks have them. It vents boost pressure back into the air intake going into the turbo. They don't call it a BOV of course. Can't remember the name right now.
i've never heard about this setup, but seems interesting... i've already seen some people working around hoses to silence the bov...
 
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