Hi.
Which system has better - spool time, controlling boost, less back pressure, higher efficiency? Which is lighter, stronger and simple?

2 slightly different ways to accoplish the same thing(from my experience).

VNT being(in the case of the Garrett GT3782VA from the 6.0L Ford powerstroke) 9 vanes that pivot on a unison ring to change the angle of the exhaust hitting the turbine wheel and also altering the a/r.

VGT being(in the case of the Holset HE351VE from the 6.7L cummins) a large slide that restricts the exhaust by moving linearly in/out.

There is one moving part in the exhaust with the Holset and 11 in the Garrett( 9 vanes, 1 unison ring, 1 actuator). I had 0 problems with reliability with the Garrett, no experience yet with the Holset. The Holset will flow much more air though as the GT3782VA is only really good for around 400 CFM if I remember correctly. I think the Holset will do more like 600 CFM.

Are there 2 particular turbos you had in mind for a particular project?

I think to do some project with one of them but i am thinking about which system is better.

I don't know much about either, but I would have to guess that VGT is better, simply because it has fewer moving parts, thus would be more reliable.

I do like the simplicity of the VGT over VNT. I think VNT may control boost on a gasoline engine better. VGT I should shed heat better, and handle higher EGTs since all the vanes are cast together.

Beyond that I don't know, not enough stuff is out there now for any kind of real comparison. I would really like to experiment with a VNT turbo.

One thing about VNT stuff, there are a lot more sizes to choose from. In the VGT world the HE341V is the smallest I've seen. VNT goes all the way down to the VNT15 in the TDI jettas. If they can handle the heat, it opens up a lot of options for smaller engines.