• That turbo makes a lot of torque, which must be addressed in the drive line.turbo image by Elijahu from Fotolia.com
  
  Turbochargers don't increase horsepower; they increase torque (the amount of force the engine can exert per revolution). Horsepower increases only happen when the turbocharger helps to sustain torque at high RPMs. The downside of all that torque is that it also increases at fairly low RPMs, which puts a great deal of stress on the clutch and flywheel.
  
  

Strength

• By far the most important aspect of clutch selection is holding power. How well the clutch holds the transmission input shaft to the flywheel depends on three basic factors: clutch/friction material surface area (size), clutch material and spring tension. When selecting a clutch, you need to start at the minimum size/type/material/strength combination that will actually transfer all that torque to the wheels. A slipping clutch is not only detrimental to performance, extreme slippage (and overheating) can actually cause the clutch pack or flywheel to explode under certain circumstances.
  
  

Progressivity

• One very important aspect of turbo clutch design is "progressivity," or how much "play" you have between partial and full engagement. A theoretically perfect setup would allow you to slip the clutch in indefinite increments for hours at a time without overheating, but would still lock the engine and transmission together under full engagement. Unfortunately, many clutches that use material strong enough to lock a powerful turbo engine to its transmission under full throttle have little to no progressivity; they're either on or off. An on/off clutch will make the car difficult to drive and prone to stalling, especially when the engine is "off boost." Organic material clutches are very progressive, but burn easily and aren't suited for racing applications. On the other end of the spectrum, sintered (powdered and fused) iron clutches weld themselves to the flywheel when engaged, but are about as progressive as a light switch. Kevlar can clamp very powerfully and progressively but can easily be ruined by overheating. Carbon ceramic clutch material can withstand almost as much power as sintered iron but is much more progressive. Although ceramic clutches are a little "notchy" during engagement, they offer perhaps the best compromise for a powerful turbo car.
  
  

Drivability

• Single-plate turbo clutches often require very strong springs to engage while the engine is under boost, which can be a serious pain in the quadriceps when it's not. The fact is that unless you're driving a mid-1990's F1 car on the street, you're going to spend 99 percent of your time well below full boost. One way to keep your clutch strong and your left leg happy is to increase clutch surface area by using a two- or three-disc clutch pack. In theory, using a triple-disc clutch pack (which will actually only increase surface area by a factor of about two) should get you the engagement power of a single-plate setup with a spring that's twice as stiff. The triple-plate's lower spring pressure equates to a huge difference in comfort and effort when driving in stop-and-go traffic.