I’ll be the first to admit I really don’t know much (okay, I don’t know anything!) about the mechanical workings of a car. I can stumble through a stereo install, maybe change the oil, and drive the thing. That’s about it. I wish I knew more, which is probably why I regularly dream about buying an old 911 or 912, tearing it apart and figuring out how to put it back together in working order. My wife reminds me this really would NOT be a good idea.
For now, I’m trying to learn a bit more about what makes Porsche cars such technological wonders. Today I ran across a couple of articles about Porsche’s Variable Turbine Geometry (VTG) and thought I’d post up my non-mechanical summary along with some links in case any others want to join me in the virtual mechanic’s garage.
Variable Turbine Geometry has actually been around for a while now and used in turbo diesel engines since the 90s. Porsche’s inclusion of VTG in it’s 2007 911 Turbo (997) is the first time it’s made it into a production gas vehicle. This is because the material used to make VTG turbos couldn’t withstand the hotter exhaust gases from the gas engines. Porsche solved this problem by using a BorgWarner VTG turbohcharger in the 997 911 Turbo. The BorgWarner VTG turbocharger uses special materials borrowed from the aerospace industry that are able to handle the increased temperatures encountered.
The biggest problem with turbochargers of old is that big turbos take too long to spool up, especially at slower engine speeds (remember the big turbo lag complaints in the old 911 Turbos?). Small turbos on the other hand spool up fast, but run out of juice quickly. VTG solves this problem through the use of variable vanes allowing the turbocharger to respond differently depending on what is needed at that moment.
In non-mechanical terms, it’s like multiple turbochargers in one. Making the latest 911 Turbo even more of a rocket. Here’s what Porsche has to say about the real world effects of VTG:
Maximum torque is reached at lower rpm and is retained across a wider rev range. A full 460 lb.-ft. is available from as low as 1,950 rpm up to 5,000 rpm. Every throttle input is met with exceptional response and phenomenal acceleration. [Via Porsche.com]
We all could use a little more “phenomenal acceleration” in our lives!
If you want to read more, check out the following articles:
PaulTan.org – Paul has a nice little post with some great pictures and illustrations. Start here.
MotionTrends.com – A decent article on VTG with some pics and an overview of 100 years of turbochargers.
Porsche.com – A good technical explanation, but a bit over my head.
BorgWarner’s Site – Again pretty technical, but straight from the horse’s mouth.