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have a look a this link I thinck it mentions something about, The unique ported shroud was designed to minimize compressor surging at the mid-range rpms.

http://www.dragsport.com/issue/2006/0706_tech.shtml

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RBSandy they are the vent paths for the ported shroud within the inlet boss . 2rismo I'm not sure what you mean by they are covered by the filter or inlet ducting ? So long as the vent paths can vent air from the radial slot in between the main and splitter compressor blades to the atmosphere side of the boss they will work . I have a feeling that HKS do this partly for bling factor (marketing) but I also get the feeling that doing it like this or by having the trumpet mouth insert like say their GT3037's have reduces the shrieking screaming noise that the more common port shroud like say a GT30R (GT3076R) tends to have .

Thanks for the link as well , always wanted to see inside the HKS TO4Z comp cover .

Cheers A .

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the holes on the comp cover are a workaround for compressor surging

it allows air to enter onto the compressor wheel on the outer edge to balance out the some of intake sucking, which is commonly associated with surging. think of it as an anti surging device.

the bulk of the air enters the snout, thanks to the vacuum effect of the compressor wheel sucking in air, but a very small amount enters through the holes also to side step around surge

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wonder if it would surge with the holes blocked off. logic would say yes.

i guess that was the only comrimise they could come up with to avoid surging. must be a really wacko compressor/housing combo (sounds logical??)

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It's not very hard to picture. How many of you run no filter on your turbo? Do you all have a pipe from the compressor inlet to an air filter? Would the holes be obscured/covered on a T04Z like this?

Tell me what they're for in that situation?!?!?

Adrian

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2rismo I can't follow you logic , if you mean "covered" as in out of sight then 99.99% of port shrouded compressor covers the world over are covered . This does not prevent them working as they were designed to . Many Diesel turbos have port shrouding and very rarely are they run without ducting to an air filter . If the manufacturer wanted it not to work the gas ports would exit the cover through the outside of the boss ie the parallel section behind the barb .

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asmuch as i would like to believe that its just bling factor, HKS have obviously done some R&D into this turbo with a particular housing combo and realised it surges, whether its engine and boost specific or whatever. 2rismo, doesnt matter if thier plumbed back into the induction pipe. thier there to releave flow when its surging.

and if its all bling why wouldnt they do it with all thier other turbos?

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It's not very hard to picture. How many of you run no filter on your turbo? Do you all have a pipe from the compressor inlet to an air filter? Would the holes be obscured/covered on a T04Z like this?

Tell me what they're for in that situation?!?!?

Adrian

I dont get what you mean either, the pipe sits OVER the housing, not inside it.

So the holes, no matter if a pipe fed the bellmouth or not, would still flow air as designed

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It's not very hard to picture. How many of you run no filter on your turbo? Do you all have a pipe from the compressor inlet to an air filter? Would the holes be obscured/covered on a T04Z like this?

Tell me what they're for in that situation?!?!?

Adrian

Im not getting you either :wave:

Silicon joiner gets hose clamped to the outside of housing, holes on inside. Why would the holes be obscured?????

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