It may be the same "engine" but there is a lot more involved then a different intake...
The 3.6L Direct Injection engine is the premium engine option for the 2008 CTS. This technology on the 3.6L VVT engine contributes greatly to a 15-percent increase in horsepower; 8-percent increase in torque, and 3-percent improvement in fuel consumption. Additionally, the application of direct injection reduces cold-start hydrocarbon emissions by 25 percent and it is designed to operate with regular unleaded gasoline. The engine also helps the CTS achieve zero to 100 km/h performance of 6.3 seconds and a top speed of 249 km/h (electronically limited).
Gasoline direct injection differs from the fuel delivery process of a conventional fuel injected engine by delivering fuel directly into the combustion chamber, where it is mixed with air drawn in the chamber; the conventional design mixes the air and fuel prior to delivery into the combustion chamber. The advantage is improved fuel control and a more complete burn, which generally requires less fuel than a conventionally injected engine of the same size and configuration.
With the 3.6L direct injection engine, fuel is introduced directly to the cylinder during the intake stroke. As the piston approaches top-dead center, the mixture is ignited by the spark plug. The fuel injectors are located beneath the intake ports, as the intake ports only transfer air. Direct injection also permits a slightly higher compression ratio than if the fuel were delivered with conventional fuel injection. The result is better fuel consumption at part and full throttle. The engine uses conventional spark plugs similar to other high-feature V-6 engines.
A high-pressure, returnless fuel system is employed. It features a high-strength stainless steel fuel line that feeds a variable-pressure fuel rail. Direct injection requires higher fuel pressure than conventional fuel injected engines and an engine-driven high-pressure fuel pump is used to supply up to 1,740 psi (120 bar) of pressure. The system regulates lower fuel pressure at idle approximately 508 psi (35 bar) and higher pressure at wide-open throttle. The exhaust cam-driven high-pressure pump works in conjunction with a conventional fuel tank-mounted supply pump.
Direct injections fuel delivery enables very efficient combustion to help reduce emissions, particularly on cold starts the time when most tailpipe emissions are typically created. Also, direct injection permits a higher compression ratio 11.3:1 in the case of the 3.6L which has a positive influence on fuel economy.
3.6L Direct Injection VVT
The 3.6L Direct Injection VVT engine is based on a sophisticated 60-degree dual overhead cam (DOHC) V-6 design. It is the latest member of a growing family of V-6 engines developed for applications around the world, drawing on the best practices and creative expertise of technical experts in Australia, Germany, North America and Sweden.
Features found on the 3.6-liter VVT DI include:
Aluminum engine block and cylinder heads
Dual overhead cams with four valves per cylinder and silent chain primary drive
High-pressure, engine-driven fuel pump
Advanced multi-outlet fuel injectors developed to withstand high pressure and heat
Stainless steel, variable pressure fuel rail
Four-cam phasing (VVT see description below)
11.3:1 compression ratio
Aluminum pistons with floating wrist pins and oil squirters
Polymer coated piston skirts
Forged steel crankshaft
Sinter-forged connecting rods
Structural cast-aluminum oil pan with steel baffles
Electronic throttle control with integrated cruise control
Advanced direct injection capable engine control module (ECM)
Optimized exhaust manifolds with close-coupled catalytic converters
Fully isolated composite camshaft covers
Outstanding noise, vibration and harshness control
Maximum durability with minimum maintenance
Common manufacturing practices for efficiency and exceptional quality
The 3.6L Direct Injection VVT employs four-cam phasing to change the timing of valve operation as operating conditions such as rpm and engine load vary. The result is linear delivery of torque, with near-peak levels over a broad rpm range, and high specific output (maximum horsepower per liter of displacement) without sacrificing overall engine response and driveability. When combined, direct injection and cam phasing technologies result in an unmatched combination of power, efficiency and low emissions in gasoline V-6 engines.
Cam phasing pays big dividends in reducing exhaust emissions by optimizing exhaust valve overlap and eliminating the need for a separate exhaust gas recirculation (EGR) system.
By closing the exhaust valves late at appropriate times, the cam phasers allow the engine to draw the desired amount of exhaust gas back into the combustion chamber, reducing unburned hydrocarbon emissions. The return of exhaust gases also decreases peak temperatures, which contributes to the reduction of oxides of nitrogen (NOx) emissions. In tandem with the dramatic 25-percent reduction in cold-start hydrocarbon emissions brought on by direct injection, the 3.6L Direct Injection VVT V-6 surpasses all emissions mandates, and does so without complex, weight-increasing emissions control systems such as EGR and air injection reaction (AIR).