There are threads suggesting a 4 digit number associated with many Borg Warner turbos gives compressor wheel exducer diameter and inducer diameter as a percentage of the exducer diameter. For example some of the older K03 turbos may have '2075' as this 4 digit number. The exducer is 2.0" in diameter and inducer is 75% of this. This formula doesn't always seem to work, but on the MCS turbo, it seems to add up and correspond well with numbers for some other (older) K03 dimensions.

The number on my turbo is 4972. Assuming the formula above, and assuming the 49 corresponding to the exducer is in millimeters, not inches, you get the following:

-->inducer = 35.3mm, exducer = 49mm giving a calculated 52 trim.
In inches, this is 1.389"/1.929"
-This is just slightly bigger than a mitsu 09B wheel - giving a predicted flow of 275-285 CFM or somewhere around 21.3 lb/min.

I know it's really rough comparing to an old compressor wheel from a different manufacturer, but it's driving me crazy not having a compressor map for this particular turbo. 21.3 is lower than I would like so I hope this is wrong. If the compressor wheel dimensions above are corrrect, I bet the actual flow is within 10% of the 21.3 number.

My follow-up question - Has anyone measured these dimensions???

-my 0.0199992

 

Going a little too technical... I'm from the VW world.... KKK turbos SUCK imo. Bad on spool, even on a k03 or k04 (have you ever seen how small it is??)... they're peaky and crap. The new engine management fixes a lot of problems, along with twin scroll. The turbo inlet pipe is the size of a quarter. Seriously. Can we get some garrett GT series love? *cough* alta *cough*

 

Based on the 9.4Lb/Min flow rate the stock turbo reaches full spool [with a 2.1:1 PR], and it's apparent upper limit of flow rate [~22Lb/Min] vs. pressure ratio, I'm comfortable in saying the stock R56 MCS K03 is comparible in sizing to Garrett's GT2052-1. This is so small it's not even a ball-bearing GT series.

 

W3rd! It's only a matter of time. the 2 liter FSI VW engine has been here for 2+ years and only now are we really starting to see progress from Garrett, APR, AWE in regards to big tubo (i.e. 28 series) upgrades. It will happen when more and more R56 tuners realize the absolute and inherent limitations of the K03 and even the K04.