To help make more power and...
To help make more power and protect the engine from detonation, an intercooler is used to cool the IAT. When coming out of the turbocharger, IATs can measure between 250 and 375 degrees. An effective intercooler can lower that IAT to 150 degrees or lower before it enters the intake manifold and the engine.
"The key is to keep duration and overlap to a reasonable level," Squires says. "Lobe centers on turbo cams are typically going to be in the 114-116 range, and duration at 0.050 inch is typically not going to exceed 230 degrees. Too much valve overlap will leave your cylinders contaminated with exhaust and rob you of significant amounts of power."
Going along with the camshaft choice is the accompanying valvetrain, specifically the valvesprings. With high lift, without question better valvesprings are needed. If you were running the stock cam, however, you would think the stock springs would work, right? Think again.
"We typically see stock valvesprings start to float around 7-9 pounds of boost," Squires says. "The added intake and exhaust pressure will tend to hold the valves open and rob you of top-end power. Changing the springs is relatively easy and inexpensive, and will help when using the stock cam or cams."
Other Aspects of Turbocharging
Sorry to inform you, but we aren't done yet. We haven't talked about blow-off-or bypass-valves, turbo maintenance, and intercooling. Grab something to drink because we might be here all night.
The wastegate bleeds off boost pressure to keep the boost level and turbo speed in check, protecting the engine. But what protects the turbo when the throttle is slammed shut? A simple device called the blow-off valve. Also known as the bypass valve, this component bleeds off pressure in the intake tubing while allowing the turbo to freewheel. This prevents the boost from causing reversion that can slam into the compressor wheel, causing crazy harmonics when the throttle is shut under boost.
"This component (the blow-off valve, or BOV), dumps the boost out of the intake tubing during a specific condition, which is when there is boost in the intake tubing and vacuum present in the manifold," Squires says. "This is a condition that occurs mostly in a manual-transmission car during a shift. If the BOV is used, the turbo will freewheel during shifts and maintain most of its turbine rpm. Without the BOV, the turbine can dramatically reduce its rpm, which would require more spool-up time when the throttle is applied in the next gear. At high boost level-15 pounds or more-this component becomes critical in turbocharger longevity and prevents a condition called compressor surge, which can damage the turbo."
"Once the throttle is closed after positive pressure is achieved, there is a pressure buildup that occurs between the turbo and the closed throttle blades," Page says about compressor surge. "To prevent that pressure buildup from abruptly stopping the turbo, it must be relieved.
Another important part of utilizing a turbo is maintenance. A turbo is lubricated by oil plumbed from the crankcase, so the oiling system must be properly set up and oil changes must be made on time. "Providing adequate oil pressure and flow through the turbo prevents it from damaging itself in the harsh environment in which it lives, which is one of extreme tempera-tures and extreme rpm," Squires says. According to the experts, that 3,000-mile oil change you are supposed to make should be shortened to 2,500 miles and not missed.
Idling down the turbo isn't needed if you operate the car under normal driving conditions. If you are planning on using the car mostly at the strip, however, idle it after use or employ a turbo timer. If you don't, oil will heat up dramatically in the super-hot turbo and can burn, dramatically shortening its life.
In an effort to make more power and keep the engine out of detonation, use of an intercooler is a no-brainer. An intercooler is a component that lowers the temperature of the intake charge after it comes out of the turbo and before it enters the engine. There are two common types of intercoolers available: air-to-air and air-to-water. You can also employ the usage of a methanol injection system to cool the intake charge.
"Since compressing air increases the temperature of the air, an intercooler is typically used to reduce the temperature of that air," Squires says. "We typically see about a 1/2hp gain for each degree that you can drop the intake's temperature, so an intercooler is a good investment. Lowering the intake temperature also lowers cylinder and exhaust temperatures, which reduces the risk of detonation and cylinder damage."