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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
Originally Posted by RarlyL8 View Post
...The compromise was to use a slightly over-sized pipe exiting the turbo outlet...
Intuitively that sounds like a reasonable compromise and I do not know if we are talking big or little differences.

As to that, the above Turbo Theory article says:

" There's more to it, though-- if a larger bellmouth is excessively large right at the turbine discharge (a large step diameter increase), there will be an unrecoverable dump loss that will contribute to back-pressure. This is why a gradual increase in diameter, like the conical diffuser mentioned earlier, is desirable at the turbine discharge. "

Also most of us do not seem to be concerned with the increase in exhaust back pressure that comes with the small hot sides and big compressor wheels that are the rage. They make for early boost and extended the boost up top but possibly at the expense of lost VE or HP. It would be interesting to see a back to back or measured back pressure using the 7200 v 7006 turbine wheels. The fact that we are seeing some over-boost with the newer big turbos with some using a .8 bar spring to deliver 1 bar boost is kind of part of this I suspect.

Old 03-15-2009, 01:09 PM
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