Twin Turbo V6 Vs. V8

by Richard Rowe

That old adage about there being no replacement for displacement is beginning to look more time-worn than time-tested. Twin turbo V6's are making serious inroads into the performance community, competing with and even surpassing many competitive V8 designs in many ways. However, in 2010, the differences between the two aren't as great as you might think, at least in stock form.

Comparison

The Nissan GT-R's VQ-based 3.8L V6 puts out between 480 and 500 horsepower (each engine is hand-built, so there's always some variation), making it a good match to the 7.2L Corvette LS7's 505 horsepower. Ford's new 365 horsepower, 3.5L Ecoboost V6 (as used in the Ford Taurus SHO) would similarly give the new Camaro's 400 horsepower, 6.2L L99 a run for it's money.

Basic Differences

V8's like those mentioned above rely on the vacuum created by falling pistons and atmospheric pressure to draw air into their cylinders. This approach has worked well for many years, but such "natural aspiration" doesn't work efficiently all the way across the engine's RPM band; power is generally biased to either low-end torque or high-end horsepower. Turbocharged engines (which use a compressor to shove air into the cylinders) can get around most of the RPM biasing with careful tuning and good turbo selection.

Torque

Naturally aspirated V8s tend to have a fairly bell-shaped torque curve, which tends to start out fairly low and creep upward to a peak; after that peak, torque tends to taper off toward the engine's redline. Because they use two small compressors (turbos), twin-turbocharged engines tend to make huge torque at low RPM and maintain it well throughout the RPM band.

Flexibility

An engine's "powerband" is loosely defined as the area between the peak torque and peak horsepower. The wider the gap between these two peaks, the more useable and flexible the engine will be while driving. Twin-turbo engines (like the VQ and Ecoboost) triumph in this area, with a 3,000 and 2,000 RPM spread respectively. The LS7 and L99 only manage a 1,300 and 1,800 RPM powerband.

Average Power

There's more to engine potential than just peak numbers; average power (power produced all through the RPM band) has a huge impact on performance. Although the LS7 and VQ may produce almost identical horsepower and torque figures, the turbocharged engine maintains over 400 ft-pounds of torque for a whopping 3,000 RPM (compared to the 1,100 RPM of the LS7). Although the LS7 and L99 aren't quite as "peaky" as older and less sophisticated designs, they still make comparatively little power outside their peak zones. The turbo engines ability to maintain more power across the RPM band makes for a quicker car on the racetrack and the street.

About the Author

Richard Rowe has been writing professionally since 2007, specializing in automotive topics. He has worked as a tractor-trailer driver and mechanic, a rigger at a fire engine factory and as a race-car driver and builder. Rowe studied engineering, philosophy and American literature at Central Florida Community College.

Photo Credits

  • photo_camera corvettes image by michael langley from Fotolia.com