NefMoto

I was looking for a theoretical base for tuning my boost curve, and found some usefull documents on the Garrett website. Since I did not feel like typing all the numbers in my calculator all the time, I made an excel file that helps a bit. Nothing fancy, but it works  :) If/when I ever find out how I can graph these numbers into an overlaying line graph onto the compressormap, I'll update this, but in the mean time just plot the data manually onto your compressor map of choice  ;D
(If you like to work with imperial system, feel free to adapt. I added some conversions for metric)

Example of how I plot the data in paint  ::)
(http://i284.photobucket.com/albums/ll32/tijnvanesch/228020compressor20plot20LPG_zps52ycaeff.jpg) (http://s284.photobucket.com/user/tijnvanesch/media/228020compressor20plot20LPG_zps52ycaeff.jpg.html)

ecuxplot will plot flow vs pr

I've clicked the button once, but I dont recall that it made any sense to me at the time. Does it consider VE and BSFC? For me it is important to choose different settings because I tune on various fuels...

Neither apply to pr vs airflow plots.

The main question is we have no way to measure compressor outlet pressure - IC drop is the main source of inaccuracy.

Well, VE does actually influence the amount of air that will flow vs a given PR. (But I understand in EcuXplot this is integrated because it plots from actual data)
About the pressure drop, yes that is the missing piece (as is VE actually)I have accounted for it in the calculations, but I have not measured my actual setup. I was actually discussing this with a friend today, about the possibility the pressure drop acts as a percentage either than an offset when airflow increases. My guess is that on the intake side, the vacuum between filter and turbo will increase when the turbo is sucking in more air than the filter will flow.. Anyone measured this? Or just measure vacuum at maximum flow and use it as a worst case scenario..
I did read about one user here that installed a compressor outlet pressure gauge, I could tap into the compressor housing and record my gauge, this will give a real world comparison of my personal setup :-)
(Come to think of it, I will actually do this before I change my intercoolers)

I measured some pre-turbo pressure drop.

Post (http://www.myaudis4.com/2015/10/09/pre-turbo-pressure-drop/)

Excellent imperical info, this is a great way to test fow ability between intakes. It does make a performance difference, because every psi you have to overcome in the intake, you have to add to the compressor to net the same MAP. It could make the difference between surge and no surge.

If you look at how the pre vs post turbo pressure losses change the turbo PR you can see that pre turbo losses have a greater affect on the PR.

How is that possible? IC drop is on the order of 4-8 psi ... seems to me that has a much larger effect on PR (assuming PR<3) than 1 psi of intake drop.

You measured vacuum between filter and turbo on 2 intakes, what was the PR difference between the two after the turbo? That data should provide more insight on the behaviour of the post turbo pressure drop caused by pre-turbo vacuum.

I wasn't clear, I am referring to the general affect that pre turbo losses have on PR versus how post turbo losses affect PR.  I'd expect post turbo losses to be larger as you say, but for an equivalent drop in pressure those on the pre turbo side will have more affect on the PR than the same loss post turbo.

According to the formulas used by Garrett, this is not true. I am curious about the real life effects though, but I take it you did not measure post turbo pressures at the housing and manifold?

Ah yea I reread your post. Agreed 100%

As the pre turbo losses approach atmospheric pressure, holding post turbo fixed, what does the PR do?  Do the same the same exercise with post turbo losses holding pre turbo fixed, what does PR do?

Even without approaching atmospheric pressure the PR will rise more rapidly with changing pre turbo losses than with post turbo losses.  About a quarter of the way down this page (http://www.myaudis4.com/y-pipe-flow-test/) I put a chart showing what would be the typical change for some hypothetical changes to pressure losses.

My opinion is that there are more opportunities to make gains post turbo, but pre turbo changes carry more weight for an equivalent amount of change.

In reality though, post turbo drop goes up much faster than pre turbo drop, such that it DOES impact PR more.

I can't agree or disagree with that from what I know right now. It might not be that clear cut, and would be partly hardware dependent.

I was sleeping I guess  ;D yes pre turbo pressure drop has a larger effect on PR in the calculation.
But this counts also above pr3, not just below: 50/14.7=3.40 51/14.7=3.47 50/13.7=3.65
Another motivation to keep your air filter clean!

Apologies if this is a stupid question, but what variable should we log for plotting this graph?

For a 1.8t I have mshfm_w which appears to be the calculated airflow (mlhfm - mlofs offset etc.)

Also I have mlhfmm_w which appears to be the real measured airflow at the sensor.

Mlhfmm is significantly higher by around the bosch sensor offset - 200kg/h (55.5g/s)