less weight=faster.

LS4
5.3 L LS4 V8 in a 2006 Chevrolet Impala SS

LS4 can also refer to a 454 CID Chevrolet Big-Block engine of the 1970s

The LS4 is a 5,328 cc (5.328 L; 325.1 cu in) version of the Generation IV block. Though it has the same displacement as the Vortec 5300 LY5, it features an aluminum block instead of iron, and it uses the same cylinder head as the Generation III LS6 engine. The bellhousing bolt pattern differs from the rear-wheel drive blocks.

This engine is adapted for transverse front-wheel drive applications. According to GM, "The crankshaft is shortened 13 mm – 3 mm at the flywheel end and 10 mm at the accessory drive end – to reduce the length of the engine compared to the 6.0L. All accessories are driven by a single serpentine belt to save space. The water pump is mounted remotely with an elongated pump manifold that connects it to the coolant passages. Revised oil pan baffles, or windage trays, are incorporated into the LS4 to ensure that the oil sump stays loaded during high-g cornering."[6] Active Fuel Management is also used. Output of this version is 303 hp (226 kW)/300 hp on LaCrosse Super and 323 lb·ft (438 N·m).

Applications:

2006–2009 Chevrolet Impala SS
2006–2007 Chevrolet Monte Carlo SS
2005–2008 Pontiac Grand Prix GXP
2008–2009 Buick LaCrosse Super

The LS4 is a beast, and it actually has an aftermarket, the Northstar does not.