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  #1  
Old 07-24-2012, 01:21 PM
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Blowoff valve?

Has anyone experimented w/ a pressure relief valve or a throttle-off vent of the turbo? I remember seeing throttle-off venting (and combustion out of the cylinder) used to keep a turbo spooled.

Turbo Anti-lag systems - A technical description
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Old 07-24-2012, 01:57 PM
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How does a blowoff relate to out of cylinder combustion? It didn't explain how a blowoff is involved, seems it's routing air around a gasser's throttle to facilitate the out of cylinder combustion.

So it says nothing about how a blowoff might keep the turbo spooled.
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  #3  
Old 07-24-2012, 03:27 PM
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Without a blowoff valve, when you close the throttle, the compressed air has nowhere to go but back through the compressor. This causes compressor surge, which is when the compressor wheel stalls out and makes a neat warbling sound. With a blowoff valve, when the throttle is closed, the increased intake pressure is released through the valve instead of being pushed back through the turbo.

...on a gasser.

On a diesel motor, there is no throttle plate to close. The accelerator pedal modulates fuel, not air. When you let off the pedal, all that compressed air still gets pushed into the combustion chamber. This means that there is no air charge reversion, thus no compressor surge, thus no need for a blowoff valve.
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Old 07-24-2012, 03:28 PM
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Quote:
Originally Posted by aaa View Post
How does a blowoff relate to out of cylinder combustion? It didn't explain how a blowoff is involved, seems it's routing air around a gasser's throttle to facilitate the out of cylinder combustion.

So it says nothing about how a blowoff might keep the turbo spooled.
Useless on a diesel
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Old 07-24-2012, 03:29 PM
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Originally Posted by Secondaries View Post
Without a blowoff valve, when you close the throttle, the compressed air has nowhere to go but back through the compressor. This causes compressor surge, which is when the compressor wheel stalls out and makes a neat warbling sound. With a blowoff valve, when the throttle is closed, the increased intake pressure is released through the valve instead of being pushed back through the turbo.

...on a gasser.

On a diesel motor, there is no throttle plate to close. The accelerator pedal modulates fuel, not air. When you let off the pedal, all that compressed air still gets pushed into the combustion chamber. This means that there is no air charge reversion, thus no compressor surge, thus no need for a blowoff valve.
Ah you beat me to it! What he said ^.
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Old 07-24-2012, 06:37 PM
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I thought we could get surge on our diesels?
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Old 07-24-2012, 06:49 PM
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yes we can get surge. Need to look at a compressor map, there is a line on the left that if you run to close to it then it can surge.Trying to remember now if it is basically a too small turbo or too large, think too small.
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  #8  
Old 07-24-2012, 06:58 PM
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Why, and how would there be a pressure spike in your intake? It only happens in gassers because of the the throttle plate and in big truck engines cuz their turbos are equally big and need load to keep then spinning.

Last edited by Secondaries; 07-24-2012 at 07:59 PM.
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  #9  
Old 07-26-2012, 06:47 PM
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Even though we do not have a throttle plate if the engine speed drops quicker then the turbo speed, and boost pressure, we can surge. This would be like in shifting gears. this would also not be a stock setup.
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  #10  
Old 07-26-2012, 09:56 PM
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Quote:
Originally Posted by moon161 View Post
Has anyone experimented w/ a pressure relief valve or a throttle-off vent of the turbo? I remember seeing throttle-off venting (and combustion out of the cylinder) used to keep a turbo spooled.

Turbo Anti-lag systems - A technical description
Sounds like a VNT Turbo set up.
The only pics I have seen is between the Exhaust Manifold and the Turbo Charger there is a Butterfly Valve added by way of a insert with the Valve.
At lower rpms the Butterfly Valve partly block of the exhaust Gas from coming out of the Exhaust Manifold and that increases the exhaust pressure.
The increased pressure causes the Turbocharger to spin sooner than it would without the Butterfly Valve.

What is not clear is what operates the Butterfly Valve.
I guress it could be hooked to the Throttle Linkages or some how use the intake manifold pressure with some pneumatic valve to operate it.
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  #11  
Old 07-27-2012, 03:55 PM
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A diesel engine can benefit from a BOV, but for a high boost application, Engines that see WOT then no throttle.. Ie, drag racing, sled pulling. When on the track in my truck, after I cross the finish line I go from WOT to no throttle and brakes, thus getting the turbo shutter. It is bad for the bearings, the boost pressure is trying to go back into the compressor, stalling the shaft, while the turbine is still being driven by the hot exhaust. On a daily driven low HP vehicle like these Mercedes, it is pointless. It serves no purpose but a safety device to protect the turbo(s).
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