Turbocharging
How it works: Turbocharging and supercharging are forms of forced induction. Both components act as pumps that push compressed air into the combustion chambers. This compressed air charge is far denser than the air flow into the cylinders under normal atmospheric conditions. When the denser air charge is combined with an increased amount of fuel, the combination creates a more powerful burn, which exerts greater pressure on the pistons and therefore increases the engine's power output.
One of the key differences between a turbocharger and a supercharger is the way they function. Inside a turbo's snail-shaped compartments are two finned wheels, joined by a common shaft. One wheel is the turbine, spun by exhaust gases leaving the engine. As the turbine spins, so does the compressor wheel at the other end of the shaft. The compressor takes fresh, incoming air and pressurizes it into the dense intake charge headed to the combustion chambers.
The turbo's reliance on exhaust gases to operate is a good-news/bad-news situation. The good: turbo advocates call it "free power" meaning that it places no mechanical drag on the engine, so doesn't use horsepower to make horsepower. The bad: big turbos - those with the potential to make huge power - require a fair amount of exhaust pressure to spool up. The time it takes for that to occur is known as turbo lag. A drag racer can use lag to maintain traction during initial launch, but it's no fun on the streets or a road course, where instantaneous throttle response is of more value.
Turbomakers say lag is a thing of the past, since a properly optimized turbo can make power nearly instantaneously. Those in competing camps disagree, as you'll see below.
Gauging the size of the turbo and the amount of boost that's right for your car is based on a number of factors ranging from how you'll use the car, to whether or not you want to reinforce the bottom end to withstand the greater stresses forced induction will put on them. The driven end of the car makes a difference, too. Enough boost to blow off the tires in three gears can be fun in a RWD car, but scary in a front-driver.
Where it works best:
The streets, to drag race.
Bang for the Buck rating:
"If you want to get a certain amount of power for a given amount of dollar, turbocharging is the easiest way to do that."
- Doug Macmillin, Hondata
Dope:
"Power is addicting. Once you get a taste, you want more and more and more. With a turbocharger, you can run 8 psi on pumped gas on the street, go to the track, fill up with 100-octane race fuel, and then turn up the boost with the boost controller. You can't do that with any other power adder."
- Tyler Tanaka, Turbonetics
"If someone wants to spend very little money and make good power, a simple bolt-in kit is the best way. The best bang for your buck is a turbo kit. If they want push in the seat, with a really hard hit, then turbo is the way to go."
- Charles Madrid, Skunk2 Racing
"Turbos can work extremely well on a car with rear-wheel-drive. You can put a manual boost controller on it and a "press to pass" button like the Indy cars do, so you'll have an extra amount of horsepower when you need it. But it's like an off-on switch. You want something more progressive on a front-wheel-drive, because you're steering with the same wheels that you're powering with."
- Brian Gillespie, Hasport
Nope:
"There's a satisfaction that comes with building power naturally-aspirated. Anybody can slap a turbo on a motor, even a crappy one, to make power."
- Tony Shagday, Skunk2 Racing
"It's harder to kill a naturally-aspirated engine from poor tuning than with a turbo. Poor tuning will kill it very quickly."
- Doug Macmillin, Hondata
"With a turbo you supply gas, which adds exhaust, in turn creating boost, which causes more exhaust, leading to more boost and forming even more exhaust. You can keep a constant foot on the gas and the power still goes up. In the end, you wind up with too much acceleration."
- Brian Gillespie, Hasport