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Old 09-02-2019, 09:28 PM
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Tom Vaught Tom Vaught is offline
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Default Turbo A/R and what it means

I was over on the Speed talk forum for a few minutes and saw a post about A/R and what it means.

Here is the wording. Good explanation, by the way.

"The A/R ratio doesn't have units because it's actually NOT an area/radius ratio, but supposed to tell you how quickly the turbine area shrinks down to the final nozzle as it travels around the scroll- and the distance from the center of the area to the centerline of the turbo is how they decided to denote distance from the wheel. So it's really area1/area2, hence, no units. (more technically dA/dR, I suppose, but for any REAL turbine, that is NOT a constant ... not even close)

The problem I have with A/R ratio is that no one seems to have come to a consensus on which areas we are comparing. Obviously one is the turbine nozzle, but how far out is the other? Nobody designs turbine scrolls which really have a constant A/R ratio, so where on the scroll do you take that measurement? Maybe I just missed where someone decided that part?

Hence I prefer the system of simply measuring the nozzle area, even though there are similar "standards" issues there as well.

-Adrian

Garrett, Borg Warner, and others all have maps and turbo selection software and formulas but they do not go into much detail about the specific parts so Adrian (above) is correct in his post.

https://www.garrettmotion.com/racing...hoose-a-turbo/

Tom V.

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