A blow-off valve is designed to prevent compressor surge on turbo-charged engines. Compressor Surge occurs when the engine's THROTTLE PLATE is suddenly closed, giving the Charge from the Turbo compressor, no where to go. So the blow-off is plumbed in somewhere between the Compressor's outlet and the Engine's Throttle body, allow unwanted Boost Pressure to be vented to Atmosphere or Intake stream before Compressor inlet. So, that being said, it should be obvious why most modern Turbo-charged, direct-injected Diesel Engines would have no need for a "blow off valve". A diesel engine is controlled by fuel, thus not requiring it to have a "intake air throttle plate". In a diesel engine, all mixing of FUEL/AIR occurs in the Combustion Chamber, by design the Diesel operates in EXCESS AIR situations, it can pump up to 600X times more air than it needs @ low idle. A Diesel builds peak power and Manifold Boost when UNDER-LOAD, so when you cut fuel to that engine while under load, the Manifold boost still has a place to go since the engine is still pumping air. The manifold boost tends to drop off quickly since it is being displaced by the cylinders, and since the turbine drive pressure will be less as well. This is why diesels provide higher levels of engine braking over petrol/gas engines as the amount of air to be compressed is still the same as if the engine was running at full speed and Jake brakes and other compression braking systems raise the engine braking performance even higher again.

 

wow i feel a little dumber now

 

And that proves you can copy and paste? Have you ever barked the turbo on your truck? If you answered yes... A bov will not let that happen. Soooooo I'm pretty positive it can be utilized on diesel apps as well.

 

The stacking or "surge" between shifts is not the one you want to really worry about damaging your turbo, it's the full throttle surge that really destroys it. i.e. when the turbo is under full load and trying to force more air in the engine than it can injest and putting the compressor on the left hand side of the surge line on the map.

You can look at it as a high speed resonance or vibration of the compressor wheel if you want to. Not very good.

Diesels can still make it happen and my truck will do it on stock boost, stock turbo, when lifting at full boost. Still not very damaging, but damaging some.

They do make BOVs for diesels. It will help a slight amount for keeping the turbo spinning and getting back into boost between shifts. Probably not a whole lot, but I have no experience with them on diesels. I haven't seen a whole lot of gain running with and without them on my gas engines.

Just because a diesel doesn't have a throttle plate doesn't mean you cant surge a turbo on one.

 

Red rattler- ya i copied and pasted because maybe they can explain it better than me. Sure you can use a bov if you want; but come one, for 500$+ and a kit to create vacuum or the electronics to actuate it, is it REALLY worth it? Do you see big rigs using bov's? Do you see really any medium duty diesel pickups using them? Not really.

And as guhfluh said, its the full throttle surge that hurts. And no amount of bov's is going to fix that.

 

Did you read all of my posts? Never said it was for every truck on the face of the earth. If your goin to spend 500 on one your gonna have a use for it. Also that's why bov were created... For releaving compressor surge, full throttle or not. A compessor surge is a surge no matter what. This thread is getting good...

 

And did you read MY post? I was making a generalization. Obviously there are exceptions. But in general, a bov on a diesel is silly.

 

This whole thread has gone beyond useful. Yes I read "your" post its off of a gasser website from someone elses mouth. I've had experience with them but what's that matter? Straight pipe newb to turbo expert... I give up

 

diesels have vacuum also!!!

 

Well I wouldn't say "beyond useful".. but this is a highly spoken of topic on ANY diesel board. In general bov's are silly unless on gassers. Hell, Grand Nationals didn't come with BOV's and you dont see those motors blowing (though it does become a problem with higher boost, again that vehicle is controlled by a fuel plate; our diesels are not.)

No, diesels do not produce vacuum