With more than two dozen variants of the LS engine platform already in existence, choosing the right one for your stroker build can seem quite daunting. The Gen III/IV family covers the gamut, from plebian 4.8L truck motors to the beastly 638-hp supercharged LS9. Each has its pros and cons when asked to serve as the basis of a big-inch engine build. Some LS motors boast greater displacement potential, while others feature superior cylinder head castings. As is often the case, the most desirable members of the Gen III/IV motors are the rarest and most expensive, but several run-of-the-mill alternatives are cheap, plentiful, and pack some serious power potential. To help you select the ideal LS engine for your performance goals, the following run-down includes the critical specs of every Gen III/IV small-block ever built by GM, along with a synopsis of their strengths and shortcomings in the wake of stroker buildups.
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Although the one that started it all is already a relic, no one could have predicted the impact the original Gen III LS1 would have on the hot rodding public. The LS1’s greatest asset is its revolutionary 15-degree cylinder heads, which are capable of flowing more than 320 cfm in the hands of a skilled porter. So good were these castings, in fact, that it took the aftermarket more than five years to even attempt to top the factory design. Simply massaging the stock heads and swapping in a larger cam had LS1s easily approaching the 550-hp mark in no time. Furthermore, bone-stock LS1s routinely pushed F-bodies into 12-second quarter-mile times. Although F-body LS1s were rated at 40 hp less than their Corvette-spec brethren, they essentially produced the same power, despite slight differences in cam specs. All 2001 to 2004 LS1s were upgraded from the factory with the same valvesprings and high-flow intake manifold as found in the LS6.
One of the biggest drawbacks of the LS1 is its thin iron cylinder liners that can only be bored about .010 inch over, which, when combined with a 4.000- inch crank, limits displacement to 383 ci. Anything larger requires re-sleeving the block with aftermarket liners, which isn’t cheap, but doing so enables displacement figures well in excess of 400 ci. Additionally, the standard 3.900-inch bore isn’t compatible with the latest-andgreatest GM L92 cylinder heads.
Nonetheless, as long as a 400-plus-ci build isn’t in the cards, the original LS1 provides more than enough power potential for the vast majority of hot rods.
The 400-hp LS2 was unveiled in the 2005 Corvette, and it represents the first of the Gen IV small-blocks. Compared to its LS1 and LS6 forebears, it boasts a larger 4.000-inch bore while retaining a 3.622-inch stroke, which bumps displacement to an even 6.0 liters. Making the large bore size possible are siamesed cylinder walls, which eliminate coolant passages between the cylinders. At its core, the LS2 resembles an enlarged LS6. It utilizes LS6 cylinder heads, as well as a 2001-spec LS6 camshaft. Subtle differences include a larger 90-mm throttle body (75 mm on LS1/LS6), a higher 10.9:1 compression ratio, and a different intake manifold. Interestingly, the LS2 intake manifold features slightly greater plenum volume and re-contoured runners, which actually flows less than the LS6 intake. For hot rodders, one of the key advantages the LS2 has over its smaller-bore counterparts is its compatibility with the highly desirable rectangleport GM L92 cylinder heads.
Covering the LS3’s history chronologically first requires examining the L92. This trick Gen IV mill made its debut in the 2007 Cadillac Escalade and is rated at 403 hp. Its outstanding output is largely attributable to a set of revolutionary rectangle-port cylinder heads, which borrow their basic port design from the LS7. Unlike the LS1 and LS6 heads, which are hampered by a relatively low intake port entrance, the L92 castings incorporate raised intake runners to take full advantage of their flat 15-degree valve angle. These architectural tweaks equate to 330 cfm of flow out of the box, and the heads are available for just $800 fully assembled from GM Performance Parts. (All prices represent 2011 market values.)
Blurring the line 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 using a lower-profile intake manifold, GM created the LS3 to serve as the base motor in the 2008-and-up Corvette. In addition to having a slightly stronger block than the LS2, the LS3 is fitted with a 2001 LS6 cam that’s been modified with a smidgen more intake lobe lift. The result is 430 hp and 428 ft-lbs. As with prior generations, the base Corvette motor also powers the top-of-the-line fifth-gen Camaro. However, automaticequipped SS Camaros have an L99 under their hoods, which is a slightly detuned LS3 with active cylinder deactivation that produces 400 hp and 410 ft-lbs.
The oddball of the LS family, the Gen IV LS4 was designed specifically for transverse mounting in front-wheeldrive Impalas and Monte Carlos. To accomplish this, GM shortened the LS4’s overall length—from crankshaft to flexplate—by 13 mm 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 it 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 and 303 hp. However, they’re almost as expensive as LS1s and LS6s on the second-hand market and have very limited displacement potential, so it’s of little value to muscle car buffs seeking a swap candidate.
For the 1999 model year, GM expanded the Corvette lineup by adding a stripped-down, lightweight, more stiffly sprung version of the C5 dubbed the fixed-roof coupe. When it proved to be a sales flop, GM squeezed an extra 40 hp out of the LS1 to create the LS6, and Chevrolet dropped it into the hardtop chassis in 2001, renaming the car 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 horsepower to 385 in 2001 and to 405 in 2002, 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. Like the LS1, the non-siamesed LS6 block must be re-sleeved for bore diameters exceeding 3.910 inches.
Although it falls 133 hp shy of the LS9’s staggering output, which is substantial in anyone’s book, in many respects the 505-hp 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 oldfashioned way with lots of cubic inches and airflow. In essence, it’s the ultimate factory stroker motor. The Le Manswinning factory Corvette racing program heavily influenced the design of the LS7, and, as such, it’s stuffed with loads of bona fide 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 smallblocks, 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, 11.0:1 hypereutectic pistons, and doweled steel main caps. With nearly .600 inch of lift, the 211/230-at-.050 cam is huge for stock, 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 as impressive. These CNC-ported, 12-degree castings feature 2.20/1.61-inch valves (the intakes are titanium), and they flow an astounding 370 cfm. That’s enough to put most big-block heads to shame. Best of all, factory LS7 heads flow enough to feed the largest and hungriest of stroker combinations, and they are available from GM Performance Parts (GMPP) for about $2,500. The end product 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.
The big hoss in LS land is the factory-supercharged 638-hp small-block that powers the sixth-generation Corvette ZR1. Not only is the Gen IV LS9 the most powerful engine ever conceived by GM, it easily produces the fattest torque curve of any Chevrolet motor in history. Although its torque peak of 604 ft-lbs at 3,800 rpm is very impressive, the fact that it belts out 350 ft-lbs at just 1,000 rpm is downright breathtaking.
At its core, the LS9 shares more in common with the LS3 and L92—found in base Corvettes and Cadillac Escalades, respectively—than the LS7. To enhance block rigidity, GM passed on the LS7’s 4.125-inch bore dimensions for the thicker cylinder walls afforded by smaller 4.065-inch holes. Furthermore, the block is cast from 319-T7 aluminum and features larger bulkheads, which makes it substantially stronger than previous LS units. It encases a steel crank, titanium rods, and forged 9.1:1 pistons.
With a remarkably efficient 2.3L Eaton blower huffing out 10.5 psi through a dual-core intercooler, the exotic race-ported 12-degree LS7 cylinder heads were deemed unnecessary. Instead, GM opted for 15-degree rectangle-port castings that are very similar in design to the L92 and LS3 heads, but built from more durable A-356T6 aluminum.
GMPP offers complete LS9 crate motors (PN 19201990) for about $22,000. Granted, that isn’t cheap, but it’s still a heck of a lot less than trying to replicate a motor of this caliber that’s also emissions legal and capable of lasting 100,000 miles. Although they can be hard to find, the rugged LS9 block is an excellent foundation for LS stroker buildups.
The LSA is essentially the LS9’s detuned little brother. Even so, the LSA’s 556 hp and 551 ft-lbs have helped make the 2009 Cadillac CTS-V the quickest four-door sedan to ever lap Germany’s famed Nürburgring road course. Major differences between it and the LS9 are the use of hypereutectic pistons instead of forged slugs, and powdered metal connecting rods instead of titanium units. Although the LSA also utilizes an Eaton blower, it’s slightly smaller at 1.9L and produces 1.5 fewer psi of boost. It’s a very impressive setup, indeed, but the limited production numbers of Cadillac’s top dog means there are very few LSAs to extract from your local boneyard.
As the LS6 was being developed inside GM, engineers were so enamored with its performance that they decided to adapt some of its technology to the truck engine line. By bolting LS6-style heads to a big 4.000-inch-bore iron block, GM created the LQ4. Offered as the top-of-theline gasoline engine in full-size pickups and SUVs, the LQ4 was rated at a stout 300 hp and 360 to 370 ft-lbs. In 2002, Cadillac wanted a piece of the action, too, and it added a bigger cam and more compression to boost output to 347 hp.
Due to their rugged iron blocks, generous bore diameters, and excellent cylinder heads, the LQ4 and LQ9 are among the most coveted Gen III/IV motors on the second-hand 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 or LS6.
When it came time to improve upon the venerable LQ4 in 2007, GM bolted on a set of L92 heads and increased the compression ratio to create the LY6. These simple changes increased output to 352 hp. The addition of variable valve timing helps broaden the powerband. The LY6 is currently offered for heavy-duty hauling applications in 3/4-ton pickups and SUVs. Although it’s too new to be filling up boneyards just yet, expect it to be a very popular choice among engine swappers in a couple of years.
Used primarily in light-duty trucks, the L76 is essentially an aluminumblock variant of the LY6. Major differences include a higher compression ratio and a slightly larger cam, which boosts output to 366 hp and 376 ft-lbs. Like the LY6, the L76 utilizes variable valve timing, but ups the ante even further with active cylinder deactivation. Interestingly, the L76 also powered the 2008–2009 Pontiac G8 GT. The car version of the L76 drops variable valve timing and features an LS3 intake manifold, which sacrifices some horsepower while picking up some torque.
The smallest of the Gen III/IV platform is also the least desirable. Although they’re very capable mills for their intended application and can power stock Silverados to respectable 14-second ETs, their lack of cubes makes them unlikely candidates for engine swaps. This assessment is only reinforced by the fact that they’re just as expensive as the 5.3L at the wrecking yard. The Gen III LR4 was built from 1999–2006 for fullsize trucks and SUVs, and it was replaced in 2007 by the Gen IV LY2. Other than tweaks universal to all Gen IV motors, the difference between Gen III and Gen IV 4.8L small-blocks is negligible.
Many consider the 5.7L LS1 as “the new 350 Chevy,” but that title more accurately goes to the 5.3L Vortec truck motor. As the bread-and-butter smallblock from 1999 onward, GM installs the 5.3L in the vast majority of its full-size trucks and SUVs. Considering that GM has built way more trucks than cars in the past 10 years, the 5.3L is far more plentiful and cheaper than its 5.7L, 6.0L, 6.2L, and 7.0L big brothers. At roughly $500 at your local boneyard, complete 5.3L motors can be had for a fraction of the price of an LS1 or an LS6. Price alone, however, isn’t what makes the 5.3L the biggest sleeper in the Gen III/IV camp. Its cylinder heads flow just as well in ported trim as 5.7L LS1 castings. In fact, in the early days of Gen III tweaking, before aftermarket heads became widely available, many enthusiasts preferred 5.3L heads to 5.7L LS1 heads due to the slight bump in compression that their smaller combustion chambers afforded.
For those who see the 5.3L’s smaller displacement as a drawback, it has sufficient cylinder wall thickness to easily accommodate the same 3.900-inch bore diameter as the 5.7L. Throw a 4.000-inch stroker crank in a punched-out 5.3L block, and you’ve got yourself a nice 383-ci short-block. The added durability of an iron block is tough to beat, as well. From 1999–2007, GM built several versions of the Gen III Vortec 5300, of which the LM7 is the most common. The LM4 and L33 are aluminum-block variants of the LM7, while the L59 is a flexfuel spinoff. GM began phasing in Gen IV 5.3Ls in 2005 with the launch of the all-aluminum LH6, which replaced the LM4 in mid-size SUVs. Then in 2007, the iron-block, 320-hp LY5 was introduced as an update to the stalwart LM7 for use in full-size trucks and SUVs. Also that year, the LMG and LC9 were unveiled as flex-fuel versions of the LY5 and LH6, respectively. Finally, the LH8 is a slightly detuned 300-hp 5.3L that powers the 2009-and-up Chevy Colorado pickup.
Written by Barry Kluczyk and Posted with Permission of CarTechBooks
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