Sounds like we need a kit for measuring EMP!

[Hades]

Holy sweet mother of Jeebus...
If only I was something other than a broke college student...
Thanks though

 

[Fix_Until_Broke]

I wonder if you could measure IAT with these different turbos? That's the best way to measure efficiency, at least on the compressor end.

I've got a temp sensor (0-150 C) but it's slow to respond - like 10 second time constant slow - so it'd be kind of useless for the typical driving around 3rd gear data.

I would think that mass airflow would be the best way to evaluate overall efficiency. I don't really care what temp the air is at or what pressures are made - I want to move more mass airflow, right?

 

[KERMA]

MAF, correct, but the reading you see in vag-com may not be 100% correct, because it can change indirectly thru some other maps that deal with IAT for example- and these IAT maps can vary quite a bit depending on which ecu and physical car combination. For example, there's a map or two that's coolant temp vs airflow... explained by the egr cooler configuration. (some of the "Euros" don't have an EGR cooler for instance) Then there's the offsets people like to change in vag-com, etc, so the bottom line is: MAF is calculated, while IAT is more directly measured, but they are both fundamental variables when trying to map the efficiency of your turbo. Just look at one of the old vnt-17v/a/b maps that were done back when garrett was still allied signal for example, it's always explained as isometric corrected, but nothing is truly isometric, so the comp maps you see on the garrett website for instance are kind of like a cartoon or characature without knowing IAT. The efficiency contours are derived from IAT. So measuring IAT directly, ideally before and after the compressor and intercooler is the best way IMO to get a handle on comp efficiency and which is better suited for the application under what operating conditions. I think if you do this you will find some surprising things.

 

[Fix_Until_Broke]

I wasn't thinking of vag-com data - more like a laminar mass airflow meter like you'd see on an engine development dyno.

Well, within the discussion of centrifugal compressors (turbos), yes, nothing is isometric (constant 1/densitiy) otherwise it wouldn't work very well .

I think the notes on the maps you are referring to are just a standard correction to "standard temperature and pressure" just like you'd find on a flow bench or anything else pneumatic (or otherwise highly squishy) in nature if I had to guess (without seeing the maps).