IndigoBlueWagon said:
Just to be clear: You're posting a map you "think" is from a 52mm wheel, that you "think" should behave similarly in a hybrid, and your plots are where you estimate the boost/RPM numbers should go.
That map is from the turbo from a
2.5 5-cylinder TDI (AXG/AHY; 074 145 703E) which from what I've been able to find is a VNT20
52V, I think you have the capability to check that VW part number against garret numbers and confim that, or refute it.
Second, that compressor wheel does not care if it is in a hybrid or stock VNT22, its properties regarding compression of air will remain the same.
Third, TDIMeister taught all of us how to accurately plot points on a compressor map, its fairly easy really. I have the utmost confidence in TDIMesiter's knowledge when it comes to anything automotive, I stand my my numbers as accurate. Feel free to double check them.
You say the turbo is surging at low RPMs, yet I've never had any audible or logging evidence of surge. And you estimate the turbo is out of its efficiency range almost all the time.
As was posted previously by rub87 in another thread, turbos can run a bit outside the map and not surge, but that is a fine line that most of us without big stacks of new turbos waiting in our shop don't want to play with.
BTW, if this stuff is correct, where does that leave the VNT-20? What size is its compressor wheel? If it's running 22 or 24 PSI is it surging then out of its efficient range all the time?
A VNT20 with a 52mm comp wheel running 22-24 PSI is far different. If we assume it has a tune where the redline is stock 24 PSI at redline lands just over the choke line, instead of WAY over it, besides, VNT20s from Kerma come with programming (or they used to, not sure if they still do) that reduces the boost at high revs to prevent choke, I know my tune does that and I know several others with aligator tunes that do the same thing. I've read of Jeff saying that he drops boost as revs rise to avoid choke, so I'm not sure why yours is holding 25 till 5700 RPM.
As the 20 spools slower there is also less danger of it crossing the surge line at low RPMs.