How does Variable Turbine Geometry work?
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.
August 16, 2006 @ 4:06 pm
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
August 16, 2006 @ 4:50 pm
So its something like Variable Valve Timing Turbo?
August 16, 2006 @ 4:50 pm
does BorgWarner manufacture DSG gearbox as well ? Paul, thanks for sharing all these knowledge.
August 16, 2006 @ 4:55 pm
In the cutout diagrams, does that mean that exhaust gas is recirculated into the combustion chamber?
August 16, 2006 @ 5:57 pm
here come the technology’s.
best for Paul!.
August 16, 2006 @ 5:58 pm
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!
August 16, 2006 @ 6:38 pm
i wonder can apply this technology into an evo.. sure stunning!
August 16, 2006 @ 6:42 pm
Very informative; now i know of another method car makers use to eliminate turbo-lag, thanks!
August 16, 2006 @ 7:59 pm
Now this is the way to explain a technology.
Indeed really sexy mechanical beauty, and innovative.
August 16, 2006 @ 8:42 pm
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?
August 16, 2006 @ 9:02 pm
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!!
August 16, 2006 @ 9:05 pm
And if i’m not mistaken also those little vanes from the VGT has some sort of ceramic coating.
These dudes are mental……
August 16, 2006 @ 10:24 pm
Must be very very very expensive due to the space technology material.
August 17, 2006 @ 1:09 am
Hi Paul + guys. This is my first comment on here.
If i may add, Paul you wrote:
“If you notice, some of the exhaust gas does on hit the turbine blades, instead exits through the left side of the turbine. This is where all the excess exhaust pressure goes, effectively eliminating the need for a wastegate.”
To my understanding, in the illustration the gas that does not hit the turbine blades merely goes around and comes round the other side. Remember that gasses are hitting the turbine blades at all 360 degrees.
Looking at the cutaway, the only way for exhaust gasses to exit the system is through the turbine blades, therefore for proper boost control, there seems to be the need for an external wastegate.
Please correct me if I’m wrong.
August 17, 2006 @ 1:10 am
hi guys, I have edited my post to remove the wastegate info until i can double confirm how boost is controlled without a wastegate.
August 17, 2006 @ 2:10 am
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=22873
there’s a nice gif animation of vtg in action here.
August 17, 2006 @ 10:30 am
great info Paul!
August 17, 2006 @ 1:44 pm
icic
August 17, 2006 @ 2:51 pm
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!
August 17, 2006 @ 3:16 pm
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.
August 17, 2006 @ 8:09 pm
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.
August 17, 2006 @ 8:27 pm
I cant just imagine if I can just fix one of this tech into my sisters Kancils…
August 17, 2006 @ 9:10 pm
sorento ?
fuyo , da koreans is tryin sth new long time ago .
August 19, 2006 @ 2:19 am
“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..
August 21, 2006 @ 1:11 am
[...] The new Porsche 997 Turbo’s main highlight is the new engine that comes with Variable Turbine Geometry. The 3.6 liter flat-6 engine is twin turbocharged with two VGT turbines on each bank of cylinders, as well as two intercoolers. The result is 480hp at at 6,000rpm and 620Nm of torque between 1,950rpm to 5,000rpm. Fantastic torque curve. For more information on how VGT works, check out my previous blog post “How Does Variable Turbine Geometry work?” [...]
October 8, 2006 @ 4:28 pm
[...] This particular model shown is a turbodiesel model, which can be identified by the CRDi badge on the boot – a 2.0 liter CRDi with a Variable Geometry Turbocharger, similiar to the one found in the Porsche 911 Turbo. Of course, VGT has been around in turbodiesels for quite some time already. Performance stats are 138hp at 4,000rpm and 305Nm of torque between 1,800rpm to 2,500rpm. The turbodiesel is also equipped with a Diesel Particulate Filter for better emissions. If you prefer petrol, the UK market has a 2.0 I4 CVVT and 2.7 liter V6, but in other markets there is also a 2.4 liter I4 CVVT. [...]
December 6, 2006 @ 3:21 pm
[...] The 2.5 liter Duratorq engine is a DOHC 16-valve turbodiesel unit, featuring Bosch common rail direct fuel injection and a variable geometry turbocharger. It makes 141hp and 330Nm of torque, up from the current Ranger available in our market’s 2.5 liter SOHC indirect injection turbodiesel which makes 121hp and 262Nm of torque. [...]
April 9, 2007 @ 12:44 pm
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_FREEWHEEL.jpg
February 28, 2009 @ 3:06 pm
this technology rocks dude!!!!!! can i get technical papers on vtg and r2s systems?
March 9, 2009 @ 10:59 pm
Wow! That’s a real-time, concise even fully-functionally-described piece of work.
Thanks a ton, Paul
April 7, 2009 @ 3:37 am
Excellent staightforward explaination even for an absolute novice to turbocharger technology.
August 23, 2009 @ 8:10 pm
U can include some animation figures that shows how this vanes work……