LQ4/LQ9
As the LS6 was being developed inside GM, engineers were so enamored with its performance that they decided to spread some love to the truck line as well. By bolting LS6-style heads to a big-bore iron block, GM created the LQ4. Offered as the top-of-the-line gasoline engine in fullsize pickups and SUVs, the LQ4 was rated at a stout 300 hp and 360-370 lb-ft. In '02, Cadillac wanted a piece of the action too, and added a bigger cam and more compression to boost output to 347 hp. Due to their rugged iron blocks, generous 4.000-inch bore diameters, and excellent cylinder heads, the LQ4 and LQ9 are among the most coveted Gen III/IV motors on the secondhand market. With the exception of their larger combustion chambers, the LQ4/LQ9 heads are virtually identical to the LS6 castings. Furthermore, their 4.000-inch bores enable them to be paired with GM L92 cylinder heads. By bolting a set of these budget $800 rectangle-port castings to a stock 6.0L short-block, you can make some serious power for peanuts. Unless you're excessively fastidious about saving a few pounds, it makes little sense to pass up on an LQ4/LQ9 for a comparably priced LS1/LS6.

DISPLACEMENT: 364 ci
BLOCK: Cast iron
HEADS: Aluminum or iron 15-degree cathedral port
BORE/STROKE: 4.000 x 3.622
COMPRESSION: 9.4:1-10:1
CAMSHAFT (’99-00 LQ4): 191/190 @ 0.050; 0.457/.0.466; 114
CAMSHAFT (’01-04 LQ4 AND LQ9): 196/207 @ 0.050; 0.467/0.479; 116
OUTPUT: 300-347 hp and 360-380 lb-ft
WHAT IT’S IN: '99-04 Silverado, Suburban, Yukon, and Hummer H2 (LQ4); '02-06 Escalade, '03-07 Silverado SS and Sierra (LQ9)
GMPP PN (LQ9): 19156262

LY6
When it came time to update the venerable LQ4 in '07, GM bolted on a set of L92 heads and increased the compression to create the LY6. These simple tweaks bumped output to 352 hp. The addition of variable valve timing helps broaden the powerband as well. The LY6 is currently offered for heavy-duty hauling applications in 3/4-ton pickups and SUVs. While it's too new to be filling up boneyards just yet, expect it to be a very popular choice amongst engine swappers in a couple of years.

DISPLACEMENT: 364 ci
BLOCK: Cast iron
HEADS: Aluminum 15-degree rectangle port
BORE/STROKE: 4.000 x 3.622
COMPRESSION: 9.67:1
OUTPUT: 352 hp and 382 lb-ft
WHAT IT’S IN: 3/4-ton '07+ Silverado, Sierra, Suburban, and Yukon