Turbo Snails

Posted by admin on Wednesday, August 9, 2006 · Leave a Comment

Turbo Snails

Turbochargers: the best power for your penny

Few would debate that the Ford Taurus of past generations was about as unexciting and commonplace as a loaf of bread. But the new Taurus SHO (Super High Output) is attempting to shatter that dull image with the vibrancy of a very potent 365 horsepower engine. But this Ford offers more than just power. One of its main selling points is that this new Taurus has the power of a V8 and the fuel efficiency of a V6, in this case a 3.5 liter “ecoboost” V6. How did Ford manage to strike such an ideal compromise between horsepower and efficiency, and between excitement and utility? It certainly wasn’t due to new, innovative engineering, nor cutting-edge technology. They simply did what most car companies (including themselves!) did back in the late 1970s and early 1980s in response to the energy crisis: they added a turbocharger (two in the case of the new SHO) to an existing engine in their lineup.

Turbochargers allowed car companies to use eco-friendly, efficient, and small four-cylinder engines without completely sacrificing power. But as the energy crisis and obsession with efficiency and gas mileage waned in the early 1990s, naturally aspirated V6s and V8s (without turbos) made their triumphant return. Only a few manufacturers, such as Audi/VW, Volvo, and perhaps most ubiquitously, Saab, continued employing the proven formula of small turbocharged engines. And anyone familiar with Saabs knows of their legendary fuel efficiency—and it’s no coincidence that their cars used small turbocharged inline-fours almost exclusively.

Without a doubt, today the turbocharger has whooshed its way back into engine bays, and this time it seems that it will be here to stay. These new turbo engines are much more performance-oriented than their predecessors, and have found their way into sporty cars instead of pedestrian ones. Budget imports like Subaru’s WRX and Mitsubishi’s Lancer Evo, and domestics like the Dodge Neon SRT-4, all use turbos. The immense popularity and affordability of these cars, their reputation for thrilling performance, and movies like The Fast and the Furious, which abounds with turbocharged cars chirping their blow-off valves, have created a generation of car tuners lusting for that oversized snail lurking beneath the hood.

Above all, turbocharging in its various guises has become such a popular modification because it is by far the best bang-for-your-buck, assuming you know what you’re doing, of course. A large intercooler conspicuously showcased behind the front bumper, the “pshh” sound of a blow off valve between gear shifts, and the intoxicating, jet-like sound of a spooling turbo are all bonuses that tastefully alert any tuner to the fact that your car is packing a lot more than your average import.

Obviously, a turbo kit is a desirable upgrade for anyone looking to substantially augment their car’s power. But what exactly is a turbocharger, and what’s so special about it? At its most basic level, a turbocharger is simply an air pump/compressor driven by hot exhaust gases. On non-turbocharged engines, the exhaust gases from the engine run uninterrupted through an exhaust manifold(s) and through the rest of the exhaust system and out the tail pipe.

A turbocharged engine is a bit more complicated. On such an engine, instead of flowing straight through to the muffler, exhaust gases first travel through an exhaust manifold (turbo manifold), which collects and directs all of the exhaust gas into a large opening of the turbo that leads to the exhaust turbine (see picture below). From here, some of the gases flow out of the back side of the turbo, through a down pipe, and out the muffler like in a naturally aspirated engine. But the majority of the hot gases flow into the exhaust turbine, and in doing so the moving air spins the exhaust wheel (a small metal fan with many blades) inside of the exhaust turbine. This moving air causes the wheel to rotate very quickly—sometimes as high as 120,000 RPMs. The exhaust wheel sits on a shaft that rotates with it; on the other end of the shaft there is another wheel, known as the compressor wheel. This wheel spins at exactly the same rate as the one in the exhaust turbine, but it does nothing with the exhaust gases. Instead, ambient air is drawn through the turbocharger’s inlet pipe, where the rapidly moving compressor wheel literally compresses the air above atmospheric pressure, and then sends it out of the compressor’s outlet, where it then flows to the inlet of an intercooler en route to the engine’s throttle body and intake manifold.

The amount that this air is compressed varies widely depending on things like the stoutness of the engine’s internal parts and the fuel and engine management systems. This amount is measured in pounds per square inches, and is commonly known as “boost.” So low boost is around 5-10 psi (above atmospheric pressure), medium boost is around 10-15 psi, and high boost is 15-20+ psi. While this is a huge over-simplification, the more boost a certain engine produces, the more power is generated. In general, an increase of about 10 horsepower accompanies every 1 psi increase in boost. Right off the bat, it’s obvious that a lot of power can be made from boost—at only 5 psi the engine would still be producing roughly 50 more horsepower than if it did not have a turbocharger. Compare this power increase with what could be had by a set of expensive, difficult-to-install camshafts on a non-turbo engine, which might afford the engine 10-15 horsepower more, and it is obvious that turbocharging is the way to go for serious power increases.

Be sure to come back soon to the Raleigh Tuner Car page for the step-by-step process of turbocharging the engine of a Nissan 240sx, and in doing so increasing power from 155 to 400+!

Questions? mformeister@cox.net

About the Author

Marc Formeister is a Phi Beta Kappa graduate of the University of North Carolina at Chapel Hill. He has a bachelor’s degree in English and has been heavily modifying cars for almost a decade.

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