LS6
First introduced in the '01 Corvette Z06, the Gen III LS6 is basically a hopped up version of the LS1. In fact, it shares much more in common with the LS1 than the LS2, LS3, or LS4. Compared to the LS1, the LS6 boasts improved cylinders heads, a larger camshaft, a better-flowing intake manifold, a more durable valvetrain, a bump in compression, and stronger main bearing bulkheads. Furthermore, the LS6 head design features a raised port floor, and a smoother transition at the short-turn radius for improved flow. The exhaust ports were also altered from an oval to a D-shaped design. These mods bumped hp to 385 in '01, and to 405 in '02 thanks to an even larger cam. There was a time when factory LS6 heads were the hot ticket for enthusiasts, but the design has long been superseded by superior factory and aftermarket offerings.

DISPLACEMENT: 346 ci
BLOCK: Cast aluminum
HEADS: Aluminum 15-degree cathedral port
BORE/STROKE: 3.900 x 3.622
COMPRESSION: 10.5:1
CAMSHAFT (’01): 204/211 @ 0.050; 0.525/0.525; 116
CAMSHAFT (’02+): 204/218 @ 0.050; 0.555/0.551; 117.5
OUTPUT: 385-405 hp and 385-400 lb-ft
WHAT IT’S IN: '01-04 Corvette Z06, ’04-05 CTS-V
GMPP PN: 17801268

LS7
Granted it falls 133 hp shy of the LS9's staggering output-which is substantial in anyone's book-but in many respects the 505hp LS7 is an even more impressive engineering feat. Without the assistance of a factory-installed blower, the Gen IV LS7 gets the job done the old-fashioned way, with lots of cubic inches and airflow. Its design was heavily influenced by the Le Mans-winning factory Corvette racing program, and as such, the LS7 packs loads of bonafide race-bred hardware. To achieve its epic 427 ci of displacement, the LS7 incorporates press-fit iron cylinder liners in lieu of the cast-in sleeves found in lesser Gen III/IV small-blocks, which enables boring the block out to 4.125 inches. The short-block is further fortified with a 4.000-inch forged steel 4140 crank, titanium rods, 11:1 hypereutectic pistons, and doweled steel main caps. With nearly 0.600 inches of lift, the 211/230 @ 0.050 cam is just epic, and the dry sump oil system is simply unheard of for a production motor. Displacement is just half of the battle, and the LS7's cylinder heads are equally impressive. These revolutionary CNC-ported 12-degree castings feature 2.20/1.61-inch valves (the intakes are titanium), and flow an astounding 370 cfm. That's enough to put most big-block heads to shame. Best of all, these castings are available from GMPP for about $2,500. The end product of all this pimp hardware is a motor that revs freely to 7,000 rpm and spits out 505 hp, which makes it the baddest naturally aspirated small-block ever built.

DISPLACEMENT: 427 ci
BLOCK: Cast aluminum
HEADS: Aluminum 12-degree rectangle port
BORE/STROKE: 4.125 x 4.000
COMPRESSION: 11:1
CAMSHAFT: 211/230 @ 0.050; 0.591/0.591; 120.5
OUTPUT: 505 hp and 470 lb-ft
WHAT IT’S IN: '06+ Corvette Z06
GMPP PN: 7802397