Effectiveness of eliminating BOV with throttle body?

[wgknestrick]

Theory:
In turbocharged application, a blow off valve (BOV) can effectviely be replaced by a 2nd throttle body that is placed right in front of the turbo compressor inlet.

Why it works:
All turbo charged systems need some way of elminating compressor surge upon the throttle being closed rapidly on shifts. Normally a valve (BOV) is opened at this point allowing the compressor to vent air to atmosphere because the compressor is still spinning at a high RPM and supplying a larger ammount of air than the engine can use now that the main throttle is closed.

With a turbo throttle in front of the compressor, you can prevent the compressor from ever seeing any more air to compress as it closes with the main throttle. This turbo throttle operates as a binary valve either full open or full close

Why it is better (in theory)?:
The compressor wheel is allowed to spin in a vacuum once the turbo throttle is shut and therfore does not decellerate as much as if it were still in air (in a BOV system). This would help eliminate turbo lag on fast shifts and provide a more responsive turbo charged engine.

What do you guys think about this theory? Where are the shortcomings? Would the benefits be significant enough to justify the cost?

 

[ebola]

Intersting idea...Should be tried somedays...

 

[SMOKEY44211]

I think the idea has merit.------Phil

 

[TurboXS]

There are two types of BOV. One is the BOV you described and vents to atmosphere. Which of course can make the noise that many love to hear.

The other type is a bypass valve which recirculates the air back to the turbo. Factory turbo cars have this fitted as standard. This helps keep the turbo spinning between shifts.

Which is better, your idea or a bypass valve, I'm not sure.

 

[dcasto]

see thread thread71-177194

You'll surge the compressor.

 

[Majik]

research turbo bmw F1 engines of the late 70s and early 80's.. They did what you describe.. they also replaced turbos every race...

 

[wgknestrick]

That doesn't really mean that it was because of the throttle in front of it. Most race teams just replace them before every race for reliability reasons in many of the top organizations.

I still don't think it would surge either based on the (zero) information provided. There has to be someone who has tried this.

 

[BrianPetersen]

What about overspeed? If the turbo compressor is spinning in a partial vacuum then it will have proportionally less load on it. Obviously not a concern at idle, but there might be a part-load situation where the engine is under enough load to spin up the turbo, but the reduced intake manifold pressure means the wastegate (if it operates conventionally) will be driven closed. Might need some trickery with the wastegate controls to make this work without overspeeding the turbo.

 

[mattgti86]

Regarding the compressor surge: draw-through systems where the carbs are upstream of the compressor inlet have been used for decades, so there should be a good body of information out there for the effects of closing the throttle in front of the turbo.

Also, formula SAE competition rules require the throttle upstream of the turbo. required order: throttle --> restrictor --> turbo ...

 

[Fabrico]

The theory of running in a vacuum would certainly support the possibility of overspeeding. Some turbos designed for quicker throttle response are sensitive to this. If the turbo did not cause a lag on throttle opening then the voided air just might. Why not have the air recirculate momentarily?