recirculating dump? or run without?

[Rossp]

So anyway - to clear this up, as William said he spoke to someone who worked at Garrett, I emailed Garrett this AM, and have now got a reply. Here's what they say when asked the direct question about damage and spool up time.

Here's my email to them:

Guys

I hope you can quickly help clear up a discussion I’m having with your opinion on the matter.

I understood that adding a dump valve in the intake system will reduce compressor stall and decrease lag. Someone else is claiming that running WITHOUT a dump valve actually improves response (less lag).

Would you be so kind as to clarify the situation for me?

Thanks very much!

And their reply:

Hello Ross,

I’m not sure what you mean by “dump valve,” so I’ll address my best hypothesis which is that it is a blow off valve.

If this is what it means, then I highly recommend using one in order to reduce the occurrence of surge in the turbo and significantly increase the life of the turbo. Blow off valves should absolutely be used on gasoline engines.

I would tell the person with whom you seem to be having this discussion the same thing.

Regards,

Garrett Gearhead

I replied:

From: Dagley-Cleworth, Ross [mailto:Ross.Dagley-Cleworth@somewhere.com]
Sent: Monday, August 22, 2011 8:49 AM
To: Garrett Gearhead
Subject: RE: Turbo lag / dump valve

Hi again

I was under the impression that transient lag was reduced (ie, between shifts) – because of the buildup of pressure in the intake system forcing pressure back on the compressor wheel (stalling it).

Disregarding the damage that could be caused by not running a blow off valve, would you say the “pickup” of boost whilst shifting would be improved or worsened with a blow off valve?

Thanks very much for your thoughts thus far – it’s good to get it from “source”!

Ross

and finally, their reply:

Hello,

There will likely be some advantage between shifts to utilizing a blow off, or dump valve. It helps to keep air in the system, while preventing surging of the wheel. Your general argument is correct in that time that the wheel doesn’t have to recover from surging it time that it can be working to produce useful boost.

Regards,

Garrett Gearhead

Hopefully that settles it