Variable Turbine Geometry technology is the next generation in turbocharger technology where the turbo uses variable vanes to control exhaust flow against the turbine blades. See, the problem with the turbocharger that we’ve all come to know and love is that big turbos do not work well at slow engine speeds, while small turbos are fast to spool but run out of steam pretty quick. So how do VTG turbos solve this problem?
A Variable Turbine Geometry turbocharger is also known as a variable geometry turbocharger (VGT), or a Variable Nozzle Turbine (VNT). A turbocharger equipped with Variable Turbine Geometry has little movable vanes which can direct exhaust flow onto the turbine blades. The vane angles are adjusted via an actuator. The angle of the vanes vary throughout the engine RPM range to optimize turbine behaviour.
In the 3D illustration above, you can see the vanes in a angle which is almost closed. I have highlighted the variable vanes so you know which is which. This position is optimized for low engine RPM speeds, pre-boost.
In this cut-through diagram, you can see the direction of exhaust flow when the variable vanes are in an almost closed angle. The narrow passage of which the exhaust gas has to flow through accelerates the exhaust gas towards the turbine blades, making them spin faster. The angle of the vanes also directs the gas to hit the blades at the proper angle.
Above are how the VGT vanes look like when they are open. I’ve not highlighted where the vanes are in this image since you already know where they are, as to not spoil the mechanical beauty that it is 
This cut-through diagram shows the exhaust gas flow when the variable turbine vanes are fully open. The high exhaust flow at high engine speeds are fully directed onto the turbine blades by the variable vanes.
Variable Turbine Geometry has been used extensively in turbodiesel engines since the 1990s, but it has never been on a production petrol turbocharged car before until the new Type 997 Porsche 911 Turbo. This is because petrol engine exhaust gases are alot hotter than diesel engine exhaust gas, so generally the material used to make VTG turbos could not stand this heat. The 997 911 Turbo uses a BorgWarner VTG turbocharger which uses special materials derived from aerospace technology, hence solving the temperature problem.
I hope I have helped you understand how VTG works. Watch out for full tech details on the new Porsche 911 Turbo.
After dabbling for years in the IT industry, Paul Tan initially began this site as a general blog covering various topics of personal interest. With an increasing number of readers paying rapt attention to the motoring stories, one thing led to another and the rest, as they say, is history. An avid electronic gadget aficionado as well as big-time coffee lover, he's also the executive producer of the Driven motoring TV programme.
wow! very informative Paul… now if only our national car makers would have put their minds to more R&D instead of some crappy facelifts every few months, perhaps there would be hope yet… hahaha
So its something like Variable Valve Timing Turbo?
no
does BorgWarner manufacture DSG gearbox as well ? Paul, thanks for sharing all these knowledge.
In the cutout diagrams, does that mean that exhaust gas is recirculated into the combustion chamber?
here come the technology's.
best for Paul!.
Great and well-researched feature there, Paul!
I read somewhere that the facelift Sorento got VTG too and an increase of about 20bhp – with better FC at the same time!
The beauty of high tech advancement!
i wonder can apply this technology into an evo.. sure stunning!
Very informative; now i know of another method car makers use to eliminate turbo-lag, thanks!
Now this is the way to explain a technology.
Indeed really sexy mechanical beauty, and innovative.
May i know….. is it a fix status thingy whereby mechanically linked up, the angles will ONLY vary according to speed/acceleration/exhaust volume OR, it is actually constantly variable through the implementation of an ECU that actually calculates information then calculates the angles needed?
Thanks a lot for that! Really illumating, that was. This is really ONE awesome turbocharger…no wonder the 997 Turbo's a real cracker.
Long live forced-induction!!
Thanks again Paul!!
And if i'm not mistaken also those little vanes from the VGT has some sort of ceramic coating.
These dudes are mental……
Must be very very very expensive due to the space technology material.
Oh looks like I made a mistake about the gas recirculation. nvm that.
Paul it seems that the excess boost is controlled by the vanes. My guess is that once the engine speed drops the vanes are kept wide open so the turbine spins more slowly. Then the vanes close base to assume low rpm profile.
http://www.f1technical.net/forum/viewtopic.php?p=…
there's a nice gif animation of vtg in action here.
great info Paul!
icic
VTG technology debuts in the new 911 Turbo. Wonder where you get link to such info Paul?
Anyway, its great of you to illustrate what Porsche(or Borgwarner) have done to the turbocharger. If you look at how it works, it is actually almost commonsense way to wring out more energy from the turbocharger and in fact it has been used for some time now in aerospace but only now Porsche has managed to introduce it in the 911.
So, no, I don't think it is present in any other car, particularly in a Sorento!
SatriaGuy: actually VTG has been on turbodiesels since the 1990s, the Sorento VTG is a turbodiesel. this is the first VTG on a mass production petrol car.
there has been VTG petrol powered cars before this, but in limited runs like 500 units.
Chysler has used VNT [variable nozzle technology] turbo in th 90s. Porsche is not the first.
Germans talk crap. VW is showing off everyone that they made a supercharged turbo engine for their polo but in fact Nissan did that in 1989 in their Nissan March using K10 engine.
VTG, VNT, VATN are all the same thing like how VVTi, Vanos, CVTC, DVVT or whatever you want to call it.
I cant just imagine if I can just fix one of this tech into my sisters Kancils…
sorento ?
fuyo , da koreans is tryin sth new long time ago .
"VTG, VNT, VATN are all the same thing like how VVTi, Vanos, CVTC, DVVT or whatever you want to call it."
- u wanna rectify ur phrase or sumthin? variable valve timing and variable turbo are totally different parts..
btw paul, this is an essential info to me.. thanx a lot.. wanted to know how it works since the 911 debut..
I wonder if Twincharger is made of; Combining Supercharger and Turbocharger by cuopling them with FREEWHEEL gear transmision. It is like a bicycle, in low RPM, power is get from pedal (SC). But when riding down hill, when wheel is faster, the pedal can be free. So asume wheel is a TC, it powered wihout drag from SC anymore to the engine. Is it going to work?
http://yovitadiah.bravehost.com/TWINCHARGER_FREEW…
this technology rocks dude!!!!!! can i get technical papers on vtg and r2s systems?
Wow! That's a real-time, concise even fully-functionally-described piece of work.
Thanks a ton, Paul
Excellent staightforward explaination even for an absolute novice to turbocharger technology.
U can include some animation figures that shows how this vanes work……
My ride has VGT technology, powerfull compared to its rivals without.
VGT and wastegates are thoughtless .
My Honda B18b aircraft engines retard intake camshaft to
dynamically lower the compression ratio . This precisely controls
Turbo boost , at all altitudes .
Its an amplified effect , a slight retard of camshaft will drop boost quickly .
On takeoff , at 200 HP / 7500 rpm , a 5 degree retard will drop
H.P. to 170 .
itsss amaizing…..
Is there any difference between VGT and VTT,
As per my understanding of VGT is that there will be movable vanes near turbine which can minimise or maximise gas flow onto the turbine.
Where as in VTT I’m told that turbine blades are movable.
Please Clarify.
thats great,we have two vtg in two engines of rolls royce.but one is manual and other is automatic/digital.so i need some kind of manual or instruction for this do you help me ya??
code 2383 curent below normal or open
2387 vgt activator driver circuit (motor)mechanical system not responding or out of adjustment
2388 vgt actuator position failed automatic calibration procedure-out of calibration
9122 vgt actuator over temperature (calculated) data valid but above normal operating range- least severe
2963 engine coolant temperature high-data valid but above normal operationg range least severe level
What to check after visual checking wires and fuses both apear ok
where to get electric dignostic tree information. I hope to trouble shoot this issue
Excellent Paul! a nice read, very desciptive and illustrative
Wonderful explanation of VGT……I have never see such detailed explanation…thanks:)