Millions of Turbos Can't Be Wrong

Illustration for article titled Millions of Turbos Cant Be Wrong


SEMA reports via BorgWarner statistics that the number of direct-injected turbocharged gasoline engines is expected to keep growing, up to over two million engines by 2011. The good lot of this growth will occur in Europe, while China, Japan, and North America will also experience an increasing number of underhood hair dryers. New variable vane or variable turbine geometry (VTG) technology developed by BorgWarner and Porsche for the 911 Turbo will come down in cost and become available on more mundane machines. VTG does away with the need for a wastegate by changing the geometry of the hot side turbine vanes on-the-fly. A single turbo can boost efficiently at both low and high engine rpm. Two turbos in one! This amounts to smaller engines thinking they're much bigger, and increased fuel efficiency with no performance compromise. VTG turbochargers are nothing new to the lower exhaust gas temperature world of oil burners. Superior technology now has VTG turbochargers cooking with gas.

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TURBOCHARGED GAS ENGINES TO REACH 2 MILLION [SEMA.org]

Related:
Geneva Premiere: Porsche Rolls Out the Turbo; Porsche to Introduce New Turbine Technology with 911 Turbo [Internal]

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DISCUSSION

VTG doesn't completely replace a wastegate. And it's also more complex than a traditional wastegate.

VTG is a refinement of the variable nozzle technology that has been around for along time. The old turbo MR2 had a dual-entry turbo, which did the same thing. Twin scroll turbos are similar also.

The idea is like working with a garden hose. At high flows, you get a certain amount of pressure with a large opening. As the flows drop, the pressure drops (think of the distance the water flows out of the hose against gravity as the pressure). You can restore the pressure by putting your finger over the end of the hose. The flow doesn't go up, but the water that does come out is going faster.

So a small opening is best for low flows, a big one for high flows. These variable entry devices all do that. They maximize the use of the energy in the exhaust, especially at low flows (revs).

But a high pressure system still requires a system of bypassing the hot side vanes. That is because the power builds, the turbo pulls in more intake air, which is burned and turns into more exhaust air, which then pushes the fanes and makes even more intake air, until the turbo overspeeds and blows up.

You can make a system where the gain in airflow is lower, and thus won't overspeed (think of Saab's asymmetric turbocharging), but these systems are all inherently low pressure turbos and don't provide the kind of power boost that a turbo is good at producing.

@MurileeMartin:

Seconded. It should be etched into the rear bumper or better yet lit up at night by being printed on a lit panel between the taillights like a 944 Turbo.

@rgseidl:

Read Corky Bell's turbocharging. Book. Twin (symmetrical) turbos don't increase power or reduce lag. They're only used to make packaging the turbos easier by eliminating exhaust crossflow in V engines.

Shaft-driven superchargers are great devices for making a lot of power, but they hurt mpg a lot more than turbocharging (as turbocharging uses the otherwise wasted heat energy in the exhaust), and so don't make as much sense for the mass market.