Adiabatic Efficiency: The amount of heat generated when air is compressed by the supercharger or turbocharger in relation to the amount of the air compressed. Superchargers and turbochargers typically have adiabatic efficiency ratings of 50 to 75 percent. A 100-percent efficiency rate equals no heat generated during compression.
Air Compressor: With either a supercharger or a turbocharger, it is the fanlike device that blows pressurized air into the engine’s air inlet.
Air Density Ratio: The difference between the denser air under boost and the outside air.
Air/Fuel Ratio (AFR): The mass difference between air and fuel during the combustion process. For gasoline engines, the optimal (see Stoichiometric) AFR is 14.7:1, or 14.7 times the mass in air to fuel. A higher number indicates a leaner mix (lower fuel content in the mix). A lower AFR number indicates a richer mix (one with greater fuel content). A lean mixture (one with a higher air/fuel ratio) can lead to detonation.
Blow-off Valve: A vacuum-actuated valve that releases excess boost pressure in the intake system of a supercharged or a turbocharged engine when the throttle is lifted or closed. The excess air pressure is released to the atmosphere.
Boost: The pressure of compressed air at the intake manifold that is generated by the supercharger or turbocharger. It is generally measured in pounds per square inch (psi) or bar. A 1-bar measure is equal to 14.7 psi.
Boost Controller: A device used to limit the air pressure that acts upon a turbocharger’s wastegate actuator to control the maximum boost at the engine. It can be a mechanically or electronically controlled device.
Bypass Valve: Similar to a blow-off valve, it is a vacuum-actuated valve designed to release excess boost pressure in the intake system of a turbocharged car when the throttle is lifted or closed. The air pressure is recirculated back into the nonpressurized end of the intake (before the turbo) but after the mass airflow sensor.
Charge Cooler: A radiator-like device that is used to dissipate or reduce some of the heat generated by the compression of the boosted air charge, enabling greater power and/or helping reduce or eliminate the tendency for detonation.
Detonation: Abnormal and uncontrolled flame activity in the combustion chamber that can cause engine damage, typically due to excessive heat. In a forced-induction engine, detonation is generally caused by a lean fuel mixture, too-high compression, improper tuning, or a combination of all three.
Heat Exchanger: The radiator-like part of a charge-cooling system.
Intercooler: See Charge Cooler.
Preignition: Similar to detonation, preignition is a potentially catastrophic condition whereby heat retained in the cylinder causes the spark plug to act like a diesel engine’s glow plug, igniting the incoming fuel charge before the piston reaches the top of its stroke. A cooler air charge can reduce the chance of preignition.
Stoichiometric Combustion: The ideal combustion process that completely burns the air/fuel mixture. Generally speaking, an AFR of 14.7:1 in a gasoline engine delivers Stoichiometric combustion (see Air/Fuel Ratio).
Turbine: The part of a turbocharger that is acted upon by the engine’s exhaust gases. Hot exhaust gases flow into the turbine, spinning it. In turn, the turbine spins the corresponding air compressor that blows fresh air into the engine.
Turbo Lag: The time difference between the application of the throttle and the power boost delivered by the turbocharger.
Wastegate: A boost-pressure-activated valve that allows excessive exhaust gas to bypass the turbocharger’s turbine. It is used to control boost pressure.
Real-World Project: Larry Dye’s 1,300-hp Gen V Camaro SS
“Small” isn’t part of a Texan’s vocabulary, so it should come as no surprise that when Gen V Camaro enthusiast Larry Dye wanted to hit the street and strip with something that would make a big impression, he didn’t bother messing around with the stock 6.2L LS3 for very long. He went with a force-fed LS-based 427 engine boosted by a couple of turbos and a 200-shot of nitrous waiting in the wings for that final push over the edge.
“It makes about 1,300 horsepower to the tires,” says Dye. “That may seem like overkill for a street/strip car, but it actually is drivable. You can drive it on the street comfortably or drive it to the track, change the tires and rip off a few 9-second ETs.”
What’s even more intriguing is the deceptive appearance and street-driving demeanor of the car. Apart from the roll bar inside, the interior is pretty much stock; at least, it’s not a gutted, tin-covered race car cabin. The same goes for the exterior. There are no wings, extraneous scoops, or other race car accoutrements.
“The understated appearance wasn’t necessarily intentional, because I didn’t set out to build a dedicated race car at first. I just wanted a fast street car,” says Dye. “The car evolved from a 650-horsepower supercharged combination with the original LS3 to a twin-turbo system on the LS3, which wasn’t up to the power and punched a rod through the aluminum block. It was then that I doubled down with a new builder with a built-for-bear LSX engine, but we found the limits of that block before it was recently improved. Now, we’re using a Dart LS Next block for the foundation.”
Larry Dye’s twin-turbocharged street/strip Camaro SS runs low-9-second ETs.
With 23 pounds of boost feeding the engine in Larry Dye’s Camaro, a sheet metal intake is used for safety instead of a factory-style plastic intake that could crack or shatter. The engine makes 1,300 hp with a pair of Precision Turbo & Engine ball-bearing turbos.
Along with the Dart block, there’s a Callies Magnum forged-steel crankshaft (4.000-inch stroke), a set of Wiseco pistons (4.125-inch bores), and 6.125-inch-long Callies Ultra H-beam connecting rods. There’s also a custom-grind COMP Cams camshaft. Atop the rotating assembly sits a pair of LSX-LS7 six-bolt, high-flow ported cylinder heads delivering 410 cfm worth of airflow on the intake side and 275 cfm on the exhaust side (at 0.600-inch lift). The heads feature Del West 2.20-inch titanium intake valves and Manley Inconel exhaust valves measuring 1.61 inches, all complemented by Manley 0.700-inch-lift dual-coil valve springs and COMP
Cams tool steel retainers. They are secured to the block via ARP 2000 head studs.
It’s a solid, durable long-block that absorbs 23 pounds of boost generated by a pair of Precision Turbo & Engine hybrid 62/66-mm ball-bearing turbochargers. They blow into a Precision Metal Craft sheet metal intake manifold, where the pressurized air charge is mixed with fuel delivered via 140-lbs/hr injectors mounted in Aeromotive LS7 fuel rails. There are a couple of TiAL Q-series blow-off valves, too, to relieve pressure, along with an HKS EVC-V boost controller. The injectors are fed by a Weldon fuel pump in addition to the output from the OEM fuel pump.
The car makes this power on a street-friendly 93-octane tune, though they do use just a hint of water/methanol injection (from a custom-fabricated tank in the trunk) as a safety factor to help keep the charge temps down in the blistering Houston summer heat.
It’s a combination that has proven durable on the street and strip, proving there’s virtually no limit to boosted LS performance.
CHAPTER 2
SUPERCHARGER TYPES AND SELECTION
Superchargers come in many different shapes and sizes, but they are related by a common attribute: they generate boost pressure via an engine-driven mechanism. Typically, superchargers are driven by a belt connected to the crankshaft.
When it comes to the commercially available superchargers for LS engines, there are two basic types: