Quote:
Originally Posted by williamsvts
i dnt see how you can notice loads of lag without, as without you already have boost pressure ready when you open the throttle, without it you need to build all the pressure up from atmospheric.
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The reason is simple physics. When you come off throttle, the boost that's in that pipework tries to take the path or least resistance. During transient throttle positions, that path is into the engine (the engine draws air in, whilst there is pressure from the turbo pushing more air out). When the throttle body is closed, that air still wants to take the path of least resistance - it cannot pass the (closed) TB, so attempts to go back out the turbo compressor, trying to vent to atmosphere via your air filter. The turbo stalls because the air in the intake pipes is fighting the rotational force of the exhaust gasses still coming out of the exhaust and subsequent centripetal forces of the shaft.
The noise you hear (the flutter) is the air being forced across the compressor blades the wrong way.
The lag is caused by the turbo spinning to a STOP by these reverse forces - when the dump valve is introduced, the boost is lost, but the turbo is allowed to continue spinning, improving response.
I have listed many respected sources who have said that a dump valve should be used - including two separate turbo manufacturers (one of those being Garrett who you say your contact works for). Other than your posts, I'm yet to see anyone in a respected area of the industry vote against the dump valve.
In your last post you mention the guy had pressure without the dump valve remaining at 0.7 bar. Of course he did. There was no where for it to vent to. As it can't go down the TB, where do you think it's going to try and go? Reversing into the compressor wheel, stalling it.
I'm interested to see another perspective on the idea, but it's contrary to established and recognised industry practice - including the makers of the very components we're discussing. It's also something I've not come across in the 15+ years I've been modifying turbo cars.
