The number of variations on the popular LS engine is downright scary if you are new to the game and trying to figure out which one to grab at the junkyard or online. So let’s start from the beginning. The Gen III small-block V-8 era began with the 1997 Corvette’s 5.7L LS1. Like all Gen III and IV engines, it had the same 4.40-inch bore spacing as its small-block predecessors. The clean-sheet design had a deep-skirted block with 6-bolt mains that would be carried throughout the lineup, as well as a new firing order (1-8-7-2-6-5-4-3) and high-flowing, 15-degree cathedral port aluminum heads to top it off. The LS1 was just under 350-cubes (346cid to be exact) with a 3.89-inch bore aluminum block and 3.62-inch stroke. The rotating assembly consisted of durable hypereutectic aluminum pistons, 6.089-inch powdered metal connecting rods, and a nodular iron crankshaft. Aside from the later and higher horsepower Gen IV engines, this was also carried throughout in varying sizes. A few changes were made to the camshaft and intake, which accounted for the varying power levels from the LS1’s initial launch through its use in the Camaro, Firebird, and GTO. A higher performance version was created for the 2001-2004 Corvette Z06, dubbed the LS6, with higher flowing heads, hotter cam and an improved block. This engine was later used in the first generation Cadillac CTS-V.
In the mean time, GM had taken the original LS1 design and cast it in iron for trucks. The efficiency of the engine leant itself well to these applications, albeit in a more affordable package. The 4.8L LR4 and 5.3L LM7, L59 and LM4 have become something of internet folklore – make 1,000hp with your junkyard engine! All four share an identical block that is very rigid. The difference in displacement is due to the 3.27-inch stroke crank on the LR4. The camshaft and even the pistons vary among the five 3.78-inch bore blocks, including the aluminum L33. However, all five can be honed to 3.89-inches to use LS1 or LS6 pistons. If it is a large bore that you crave, the 6.0L blocks (LQ4 and LQ9) are the best of the Gen IIIs. These iron anchors were used in the heavier duty trucks, SUVs, and vans. Unlike the 5.7L aluminum blocks, which only take a light hone, the 4.00-inch bores could be enlarged .030 over like a typical small-block. In fact, some blocks have proven capable of even larger bores (around 4.125-inch) through magnafluxing. On average, though, any 6.0L will go up to 408 cubic-inches by taking the stroke up to 4.00-inches. Longer stroke cranks are available, but not recommended with this block because it has the shortest cylinders of the bunch. As the piston pops out of the hole (at bottom dead center) it becomes unstable and causes premature skirt wear. In case you’re wondering, the easiest way to tell the iron truck blocks apart is via the engine size cast onto the front and back of the block. Unfortunately, though, there is no way to tell the 4.8L from the 5.3L externally.
Among the Gen III engines produced from 1997 to 2007, there are essentially two to three head designs. The early design is the most common, which is based off the original LS1 (“241” casting) head. You’ll find this on every 5.3L or 4.8L truck engine. The others vary only in valve and combustion chamber size. The LS1 has 67.3cc chambers with 2.00/1.55-inch valves. Meanwhile, the “852” and “706” heads from the 4.8L/5.3L have 61.15cc chambers and 1.89/1.55-inch valves. These are more suited to high compression builds with larger valves and porting, but pale in comparison to the LS6-based “799” castings from the L33. The LS6 based designs took the cathedral design to the next level with larger intake (210cc vs. 200cc) and exhaust (75cc vs. 70cc) runners that were reshaped.
Though a “243” casting may be a rare find in a junkyard, it is easy to tell the higher flowing design by the D-shaped exhaust ports. Earlier designs are oval. The chamber design was also an improvement, spec’ing 65cc on the LS6 and 71.06cc on the LQ9/LQ4 (“035” or “317”). Fun fact: the early LQ4 heads (1999-2000) were actually made of cast iron, bearing casting number “873.” Given the cost and performance increase of aluminum heads, there is no reason to mess with these. [For more info check out the book GM LS-Series Cylinder Head Guide from CarTech.]
There was some crossover with the years, but the Gen IV officially kicked off in 2005 with the C6 Corvette’s LS2. The LS2 was essentially an aluminum version of the 6.0L truck block with flat-top pistons, LS6 heads, and an LS1 cam. It is a great motor for swaps and stroker kits, due to its exceptionally long cylinder sleeves and the power potential of the larger bore. Unlike the iron block, it will only take a .005-inch hone, so 402-416 cubic-inches is about the limit. Also in 2005, GM quietly started producing Gen IV versions of the 4.8L/5.3L truck engines such as the aluminum LH6 and LC9, iron LY5, LY2, LMG and L20. There was even a front-wheel drive 5.3L LS4, but stay away from this unless you plan on building something with a transaxle (the transmission mounting points are different). We’ll cover the difference between Gen III and IV engines another time, but for now just be aware that although parts are physically interchangeable between all generations and variations – the electronics are different.
The mighty 7.0L LS7 debuted in the 2006 Corvette Z06. This 505-horse monster used 12-degree heads with square intake ports similar to the C5.R race engine that were CNC-ported from the factory with huge 2.20/1.61-inch valves for the 4.125-inch bore. These are a rare find in a junkyard, but can sometimes be found as a take-out engine from a build (though not cheap). Perhaps the next best thing is a 6.2L L92, LS3, or L99. The L92 debuted in 2007 and was used in the truck lineup until 2014 when the Gen V took its place. It was essentially a mini LS7 with a 4.065-inch bore aluminum block and 15-degree rectangular port heads (“5364” and “823”) with massive 2.165/1.59-inch valves. The differences between the three different engines were the camshaft (variable valve timing was used in the L92 and L99), lifters/valley cover (Active Fuel Management in the L92 and L99), and the valves.
The LS3 (“821”) had hollow-stem valves, as did the supercharged LSA (“863”), which came later. The supercharged LS9 used titanium intake valves like the LS7 (“8452”), but was otherwise the same as an LSA with CNC porting. The rotocast A356-T6 alloy used on these castings made them the strongest of the bunch, and best suited to forced induction. One other Gen IV worth mentioning is the group of L92-headed 6.0L engines used in trucks as well as the Pontiac G8 GT and Chevrolet Caprice. Aside from the LY6 from the HD and ¾ ton trucks, these had aluminum blocks like the LS2. Again, the material and engine size on the exterior of the block helps differentiate which block you have. Like the LS2, the LS3/L92 block will take a 4.00-inch and slightly larger stroke for 416-427cid with the right piston selection. The LS7 was built for a 4.00-inch stroke, but can easily handle up to a 4.125-inch stroke and 441cid. The only downside is that this engine is dry sump, and requires some work if you want to convert it to wet sump. The same goes for the LS9. Additionally, these two engines, along with the LSA, can pose issues when it comes to the unique accessory drive systems. Any other engine can use a variety of OEM or aftermarket solutions for the truck, Corvette, or earlier F-body style arrangements.
There is a lot to cover, so hopefully I didn’t lose you up until this point. However, I would like to conclude by briefly discussing the engine internals throughout the generations and variations. If you are planning to use a factory camshaft with a cathedral headed LS engine, the later LS6 is usually considered the top choice at .551/.551-inch lift, 204/218 degrees of duration at .050 and a 117.5 LSA. With the rectangular port heads, the LS9 is the most aggressive of the bunch with .558/.562-inch lift, 211/230 degrees of duration, and a 122.5 LSA. The different flow characteristics of the heads require radically different designs. While these two cams may not be ideal for all combinations, they will deliver the most top end power compared to other factory cams. That said; an aftermarket cam is highly beneficial. When it comes to the rotating assembly, the pistons, rod bolts and the rods – in that order – are the weak links to the factory short-block. These are the areas to upgrade if you plan on adding higher levels of boost or nitrous. Only the LS9 received forged pistons, making the ring land a weak spot on most LS pistons for boost and nitrous. All LS rods are powdered metal except for the LSA (forged), LS9 and LS7 (titanium). Without detonation or some other failure, they typically hold up well with moderate nitrous or boost. Rod bolts, on the other hand, have been known to fail, especially on engines that see sustained high rpm. Thankfully there are aftermarket options.
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Engine Displacement Bore x Stroke HP/TQ Compression LS1 5.7L (346cid) 3.89 x 3.62 305-350/350 10.2:1 LS6 5.7L (346cid) 3.89 x 3.62 385-405/400 10.5:1 LR4 4.8L (293cid) 3.78 x 3.27 255-285/285-295 9.47:1 LM7/L59/LM4 5.3L (327cid) 3.89 x 3.62 270-295/315-335 9.5:1 L33 5.3L (327cid) 3.89 x 3.62 310/335 10.0:1 LQ4 6.0L (364cid) 4.00 x 3.62 300-325/360-370 9.5:1 LQ9 6.0L (364cid) 4.00 x 3.62 345/380 10.0:1 LS2 6.0L (364cid) 4.00 x 3.62 400/400 10.9:1 L76 6.0L (364cid) 4.00 x 3.62 361/385 10.4:1 LY6 6.0L (364cid) 4.00 x 3.62 385/400 9.6:1 LY2/L20 4.8L (293cid) 3.78 x 3.27 260-302/295-305 9.1:1 LH6/LY5/LMG 5.3L (327cid) 3.89 x 3.62 300-320/320-340 9.9:1 LC9/LH8 5.3L (327cid) 3.89 x 3.62 300-320/320-335 9.5:1 LS7 7.0L (427cid) 4.125 x 4.00 505/470 11.0:1 L92 6.2L (376cid) 4.065 x 3.62 403/415 10.5:1 LS3 6.2L (376cid) 4.065 x 3.62 426-430/424 10.7:1 L99 6.2L (376cid) 4.065 x 3.62 400/410 10.7:1 LSA 6.2L (376cid) 4.065 x 3.62 556-580/551-556 9.1:1 LS9 6.2L (376cid) 4.065 x 3.62 638/604 9.1:1
