LS3/L92/L99
Adequately covering the LS3's history requires first examining the L92. This trick Gen IV mill debuted in the '07 Cadillac Escalade, and is rated at 403 hp. Its outstanding output is largely attributable to a set of rectangle-port cylinder heads that borrow their basic port design from the LS7. These castings flow 330 cfm out of the box, and are available for just $800 fully assembled from GMPP. Blurring the lines between GM's car and truck lines of engines, the L92 was the first Vortec motor with an aluminum block, and the first GM small-block ever to utilize variable valve timing. The bump in displacement to 6.2L over the LS2 and Vortec 6000 comes courtesy of a larger 4.065-inch bore. By dropping the L92's variable valve timing capabilities and fitting a lower-profile intake manifold, GM created the LS3 to serve as the base motor in the '08-and-up Corvette. In addition to a slightly stronger block than the LS2, the LS3 is fitted with an '01 LS6 cam that's been tweaked with a smidgen more intake lobe lift. The result is 430 hp and 428 lb-ft. As with prior generations, the base Corvette motor also powers the top-of-the-line 2010 Camaro. However, automatic-equipped SS Camaros have an L99 under their hoods, which is a slightly detuned LS3 with active cylinder deactivation that produces 400 hp and 410 lb-ft.

DISPLACEMENT: 376 ci
BLOCK: Cast aluminum
HEADS: Aluminum 15-degree rectangle port
BORE/STROKE: 4.065 x 3.622
COMPRESSION: 10.7:1
CAMSHAFT (LS3): 204/211 @ 0.050; 0.551/0.525; 116
OUTPUT: 400-430 hp and 410-428 lb-ft
WHAT IT’S IN: '08+ Corvette, '10 Camaro , '08+ G8 GTP (LS3), '07+ Escalade, Tahoe, Silverado, Yukon, Sierra, Hummer H2 (L92), '10 Camaro automatic (L99)
GMPP PN (LS3): 19201992

LS4
The oddball of the LS family, the Gen IV LS4 was designed specifically for transverse mounting in front-wheel-drive Impalas and Monte Carlos. To accomplish this, GM shortened the LS4's overall length-from crankshaft to flexplate-by 13mm and streamlined the accessory drive. Furthermore, it shares the same 3.780 x 3.622-inch bore and stroke dimensions as Vortec 5300 truck motors, but is based on an aluminum block and topped with LS6 cylinder heads. Despite their displacement handicap, LS4s are relatively stout for their size, producing between 290-303 hp. However, they're almost as expensive as LS1s and LS6s on the secondhand market, so it's of little value to muscle car buffs seeking a swap candidate.

DISPLACEMENT: 325 ci
BLOCK: Cast aluminum
HEADS: Aluminum 15-degree cathedral port
BORE/STROKE: 3.780 x 3.622
COMPRESSION: 10:1
OUTPUT: 290-303 hp and 325 lb-ft
WHAT IT’S IN: '06+ Impala SS, '06-07 Monte Carlo SS, '05-08 Grand Prix GXP, '08+ LaCrosse