The fourth generation of the GM small block V8 continued on the LS platform started in the third generation. This generation added support for Active Fuel Management and Variable valve timing, although neither feature is common to all fourth-generation small blocks.
As of this writing, there are four engines in this family: LS2, LS3, LS7, and LS9.
First introduced in the 2005 Corvette and Pontiac GTO, the LS2 included several evolutionary improvements to the LS1. Rated at 400hp, displacement was increased to 6.0L (364ci). A new set of heads, a different cam, and a change to a 58-tooth reluctor wheel round out the major differences.
First used in the 2005 Grand Prix GXP, this engine displaces 5.3L and produces 303hp and 323 lb-ft of torque, features Active Fuel Management, and is available in a transverse layout for front-wheel-drive applications.
The LS7 was introduced in 2006 with the Corvette Z06. Displacing 7.0L (427 cubic inches) and rated for 505hp, the LS7 introduced a new head design (known as L92) with massive airflow improvements. Previously unheard of in the automotive manufactoring community, GM hand-built each LS7, even CNC-porting the heads from the factory! A forged steel crankshaft, titanium connecting rods and intake valves, sodium-filled exhaust valves, a dry-sump oiling system and more allowed for a 7000rpm redline.
Introduced in the 2008 Corvette to replace the LS2, the LS3 increases displacement to 6.2L, horsepower to 430 (436 with an optional exhaust), and torque to 424 (428 with the optional exhaust). LS3 adopts the L92 heads introduced with the LS7, introduces a new intake manifold, and makes further improvements to the valvetrain compared to the LS2. The block is 20% stronger than the LS2.
To be released with the 2009 ZR1 Corvette, the LS9 is essentially a supercharged, intercooled LS3 with several reinforcements and some borrowed components from the LS7. Horsepower is expected to be at least 620, with torque around 600 lb-ft. The LS9 uses Eaton's new sixth-generation, four-lobe, roots-type supercharger, which provides thermal efficiency near that of a turbocharging system, but without the turbo lag. Maximum boost is 10.5psi, with a 9.1:1 compression ratio. The block is 20% stronger than the previous LS3 block (although 2009 and up LS3 engines will use the newer, stronger casting as well). The flywheel bolts to the crankshaft with nine bolts instead of six, and the heads bolt to the block using 12mm bolts instead of 11mm. The crankshaft and main caps are forged steel. The connecting rods are titanium. The head gaskets are four-layer steel instead of two-layer. There are fins in the intake manifold to help direct airflow.