Back in the early 1990s the Gen II LT1 and LT4 engines powered GM’s hottest performance cars, but GM read the tea leaves and knew that this platform would not be able to get them where they would eventually need to be in terms of emissions, CAFE standards, or even performance. A new V-8 was needed and in 1993 work began on what would eventually be labeled the LS1. Replicating the success of the original small-block was a huge undertaking, GM kept the basic structure of a single cam pushrod V-8, but nearly everything else was reworked from the deep skirt block to the firing order. A coil-near-plug arrangement replaced the trouble prone Opti-Spark and to save weight the blocks would be cast aluminum with iron sleeves. The new LS1 displaced 5.7 liters, which pencils out to 346 cubic inches, very close to the 350-inch engines they were slated to replace.
The LS1 debuted in the 1997 Corvette and moved to the Camaro in 1998. In 1999, different versions of the LS design, such as iron blocks with varying displacements, started showing up in trucks and SUVs. Over 18 years of production GM came up with many variants suited for different applications, and the best part for those of us in the hot rodding world is that, for the most part, all the various iterations of the LS platform play well with each other in terms of parts interchangeability. Want to bolt the front drive system of an LS1 Camaro to the front of an LS3? No problem. Toss LS3 heads onto an LS2 block? Yep, you can do that to so long as you have the right intake manifold. A lot of this is possible due to the similarities shared across the LS line over the years. Some of these similarities include:
* 4.40-inch bore centers (same as previous small-blocks)
* Six-bolt, cross-bolted main bearing caps
* Center main thrust bearing
* 9.24-inch deck height
* Four-bolt-per-cylinder head bolt pattern
* 0.842-inch lifter bores
* Coil-near-plug ignition system (no distributor)
* Common bolt patterns for items like the timing cover, rear cover, oil pan, front engine accessory drive systems, and valve covers (except the early perimeter bolt heads)
The new firing order of 1-8-7-2-6-5-4-3 gave the LS1 a unique sound compared to its Gen I and Gen II cousins, and the overall size was kept close to that of a Gen I small-block making it easy to swap into almost anything. The LS1 debuted with 3.89-inch bores, a 3.62-inch stroke, hypereutectic aluminum flat-top pistons, a nodular iron crank, and 6.089-inch powdered metal rods. For the most part, this formula was carried forward through the Gen III and Gen IV engines with the exception of some of the higher performance engines. Let’s take a look at the LS engines you’re most likely to come across out there.
The LS1 (5.7L, 346ci) was the engine that started it all and was given the Gen III designation. Introduced in the 1997 Corvette and moving to the Camaro/Firebird in 1998, it was a huge departure from the previous LT1 (Gen II) powerplant and included features such as a deep skirt block, coil-near-plug ignition, and an aluminum block. For the Camaro the LS1 was rated at 305 hp and came in 95 pounds lighter than the LT1 it replaced. 1997-’98 Corvettes and 1998 Camaros had less-desirable perimeter-bolt valve cover heads. 1999 saw a move to a center-bolt design (241 casting) that was carried on through all subsequent LS variants. Around 2002, some of the LS1 engines started receiving the improved LS6 parts such as the intake manifold, heads, and stronger block. The 2004 GTO also fielded the LS1 (350 hp).
The LS6 (5.7L, 346ci) was an improved version of the LS1 and designed for the 2001 Corvette Z06 with an advertised output of 385 hp (in 2002 power ticked up to 405 hp). Manufactured through 2005, it also found its way into the Cadillac CTS-V. While it shares displacement with the LS1, it features a revised block with improved bay-to-bay breathing, greater strength, higher compression, revised pistons, and other small tweaks. The LS6 also received better (243 castings) heads, a slightly more aggressive cam, and a much improved intake manifold. The LS6 cam is the most aggressive cam GM put out for cathedral port headed LS engines.
The LS2 (6.0L, 364ci) was a large evolution of the platform and was given a Gen IV designation. The LS2 debuted in 2005 in the Corvette (400 hp), GTO (350 hp), and the concept-car-inspired SSR (390 hp). It also found its way into the Trailblazer SS (395 hp) and the Holden sourced 2008 Pontiac G8 GT (361 hp). Early LS2 engines had 24x reluctor wheels and 1x cam sprockets while later ones transitioned to the 58x reluctor and 4x cam sprocket arrangement. The increased displacement meant more power and the increased bore meant it works with LS1/LS6 heads as well as the newer LS3/L92 versions. Depending on the year and platform, the LS2 could have come with either head. While there were vast differences between the Gen II V-8 and the Gen III V-8, the differences between Gen III and Gen IV engines are nearly unnoticeable at first glance. Provisions for active fuel management were added to most of the blocks and the bore size increased to 4.000 inches. Sensors also moved around and changed a bit. For example, the cam sensor moved from behind the intake to the front timing cover and the crank sensor changed from black (24x) to grey (58x). Due to the long cylinder sleeves LS2 blocks are great for stroking, a 4.000-inch crank will make a 408.
The LS3 (6.2L, 376ci) hit the market in 2008 in the new C6 Corvette and really ratcheted up the performance with the power output jumping to 430 horsepower! More strength was added to the LS3 block (which helped handle the power from the supercharged LS9 for the ZR1 Vette). The Pontiac G8 GXP also received the LS3 (415 hp). In 2010, the relaunched Camaro SS got the LS3 (426 hp) in the manual-equipped cars and an L99 (400 hp) version with Active Fuel Management (cylinder deactivation). The increased displacement was due to a bump in bore size to 4.065 inches. Add a 4.000-inch stroke and end up with a 415ci mill.
The LS4 (5.3L, 327ci) is fairly uncommon to come across. It’s centered around a 5.3L block, like the trucks, but one that’s made from aluminum instead of the far more common iron. These were rated at 303 horsepower and were found in front-wheel-drive Pontiac Grand Prix GXPs and Chevrolet Impalas. If you need a transaxle swap LS, then this is the engine to find, if not, then it’s not a good swap candidate due to the different transmission mounting points.
The LS7 (7.0L, 427ci) was developed specifically for the C6 Corvette Z06 and is the largest LS variant offered by GM, featuring a unique 4.000-inch stroke. Its large bores (4.125 inches) required a Siamese-bore cylinder block. The LS7 is full of race ready parts and tech including titanium intake valves and rods, which helped churn out the 505 rated horsepower. It was also designed around a hybrid dry/wet oiling system (but referred to as a dry-sump system), a first for GM. LS7s were hand assembled for the Corvette at the GM Performance Build Center in Wixom, Michigan. In 2014 and 2015 the LS7 was used in the Camaro Z/28 where it was also rated at 505 hp. It can handle up to a 4.125-inch stroke (making it 441 cubic-inches), but given the extra amount of work involved with converting it to a wet sump you’re better off leaving it as is.
The LS9 (6.2L, 376ci) was the first LS variant to get a supercharger, making it the most powerful LS from GM at 638 hp. To handle the boost, the LS9 used the improved LS3 block with stronger steel main caps (as opposed to the powder metal standard LS3 main caps), larger 12mm head bolts, and forged pistons. More power was derived from the roto-cast cylinder heads and a 2.3L Roots-type supercharger. Like the LS7, it was a dry-sump engine and was hand built at the Wixom Performance Build Center. The ZR1 was the first Corvette to break the 200-mph mark, and it couldn’t have done it without the LS9.
The LSA (6.2L, 376ci) was a detuned version of the LS9 and came stuffed into the 2009 Cadillac CTS-V. It received eutectic pistons instead of the forged ones found in the LS9, a smaller 1.9L supercharger with a top mounted intercooler arrangement. Power rating for the Caddy was an impressive 556 hp. A reworked version of the LSA was used in the 2012-’15 Camaro ZL1 where it churned out 580 hp! The LSA also used nodular iron main caps for strength and, like the LS9, employed piston oil squirters to reduce piston temperature.
Vortec Truck and SUV Variants
While the performance car engines carried the LS designation, those designed for trucks and SUVs were given the Vortec name. The biggest difference between them and their car cousins were the use of iron blocks and that they were often smaller in displacement. The good news is they are plentiful in scrapyards and the iron blocks don’t mind a little boost or nitrous. They accept all the front drive systems of the car versions, although some might require a boss or two to be drilled out and tapped. There are a ton of variants out there with most using a naming convention starting with L (LQ4, LQ9, LMG, LC9, etc.). Even so, we still call them LS engines given the parts commonality and how easy they are to adapt to performance use.
The LQ4 (4.8L, 293ci) is the smallest LS ever produced. It shares its iron block with the 5.3L engine and even has the same 3.78-inch bore size. The drop in displacement comes from a shorter stroke crank (3.27 inches). It’s impossible to tell a 4.8L from a 5.3L engine from the outside.
The LC9, with its 5.3L displacement is the most common LS engine on the planet and carries a pretty retro-cool displacement of 327 cubic inches. The longer stroke (3.62-inch) is what separates it from the 4.8L and—like all LS variants—it has aluminum heads. Later versions received Active Fuel Management and some applications even received aluminum blocks.
The 6.0L Vortec is typically found in 3/4- and 1-ton trucks, and while the blocks are usually iron (LY6) there are some aluminum (L76) blocks variants out there. Widely, used, these engines can be found with Active Fuel Management as well as variable valve timing systems. Iron 6.0L blocks are the go-to block for big-boost/big-power builds. The bores can be taken to 0.030-inch over (or larger through magnetic inspection), and they can be stroked up to 4.000-inches. A longer stroke is possible, but these blocks have the shortest cylinders of the line so it’s not a great idea due to piston rock at BDC.
The 6.2L—L92/L94/L9H—coded engines are the closest you’ll find to the performance LS car engines. They have aluminum blocks and the latest in CAFE friendly tech such as variable valve timing. High-end SUVs such as the GMC Yukon Denali and Caddy Escalade got this gem under the hood. The GMC Sierra (SLE/SLT), Sierra Denali, Suburban, Avalanche, and others, also received this engine.
A key component of the LS engine’s success lies in the evolving design of its cylinder heads
Like the blocks, the cylinder heads used on the various LS engines continued to evolve over the course of the program. As John Rydzewski, Assistant Chief Engineer Small-Block Engines and former LS Cylinder Head Designer explained, “The original LS cylinder head was one of the keys to producing the airflow and future power levels that the LS is known for. We knew from the beginning we had to have great airflow so replicated ports were a must. The four-bolt attachment pattern also was key to freeing up the ports to maximize airflow. To make every port exactly the same seems like common sense now, but this represented a significant amount of trial and error work that we knew we had to get right. The head design was also the foundation for the new in plane, low friction, valvetrain. As I look back, the team that had a hand in the cylinder head and valvetrain design are some of the most respected engineers in our business, including Ron Sperry, Jim Hicks, and Dennis Gerdeman.”
Technically, you can bolt any LS head to any LS engine, but due to varying bore and valve sizes you could run into piston-to-block clearance issues. So, a good rule of thumb is that LS1 and LS6 engines can only run LS1, LS6, and LS2 cathedral port heads (and their truck equivalents). LS2 engines, due to the larger 4.000-inch bore design, allows it to run LS1, LS6, and LS2 cathedral port heads in addition to the newer rectangular port LS3/L92 heads. The LS3 engines (or any of the 6.2L based variants like the L92, LSA, etc.) can run any head except the LS7 rectangular-port heads. LS7 engines can run any LS-series head, but running the smaller heads would be nonsensical from a performance standpoint. So, for the best results make sure to match the cylinder to the bore size you’re working with.
Nearly all LS engines utilize the same cylinder head bolt pattern, which is why the heads are so easily swapped around. Most have four 11mm bolts per cylinder (for a total of 10) along with an upper row of five 8mm bolts. The LS1 engines (including the LS6) had bolts of different lengths (in regards to the 11mm fasteners), but from 2004 forward all went to the same length. To better withstand boost, LS9 engines received 12mm bolts. Also, keep in mind that each head variant requires a compatible intake manifold, so an LS3 intake won’t fit LS7 heads and so forth. Of course, there’s a nearly endless array of aftermarket heads to choose from, some of which are hybrids (cathedral ports but with large LS3 sized intake valves, LS3 port but with LS7 rockers, etc.). Here are the four main factory cylinder heads you’ll encounter.
Debuting on the LS1, the cathedral port heads were named for the distinctive shape of the intake port. Any intake manifold (LS1, LS6, LS2) will work with these heads as well as Vortec intakes from cathedral port headed variants. 241 castings (the casting number is found near the corner of the head) are the most common since they were used on every 4.8L and 5.3L truck engine as well as the early LS1s. The LS1 heads have 67cc chambers with 2.00/1.55-inch valves. Other heads you’ll run into are 852 and 706 castings, which have smaller 61cc chambers and 1.89/1.55-inch valves. These are best for high-compression builds and really need larger valves and porting work. 799 heads (65cc chamber and 210cc intake runner) are pretty much 241 LS6 heads worked over for truck engines and thus are a real treasure to find when hunting through boneyards. Aside from the casting number, they have distinctive D-shaped exhaust ports. 243 castings are harder to come across and are sometimes called LS2 heads. On the truck side, these would be 035 or 317 castings (LQ9/LQ4) and featured 71cc chambers. You may even find 873 castings from the early LQ4 engines, but they are iron and not worth bothering with. Also, the early perimeter-bolt heads (933 and 806) are far less desirable. Remember, not all 243 heads are LS6 heads, but all LS6 heads are 243 castings. True LS6 heads will have the stainless steel hollow-stem valves.
Common cathedral port production casting numbers:
933 ’97 aluminum perimeter bolt 5.7
806 ’97-’98 aluminum perimeter bolt 5.7
853 ’99-’00 (LS1) aluminum center bolt 5.7 – 66.67cc
241 ’01-’03 (updated LS1) aluminum center bolt 5.7 – 66.67cc
243 ’04-up (LS6/LS2) aluminum center bolt 5.7. Also in some ’05-up trucks – 64.45cc
373/873 LQ4 iron heads – 71.06cc
706/852/862 ’99-up 4.8L-5.3L truck heads – 61.15cc
035 /317 ’99-up LQ9 and LQ4 6.0L truck heads – 71.06cc
799 ’05-up 4.8L-5.3L truck heads (these are basically 243 heads)
L92 heads (often referred to as LS3 heads) moved to a rectangular port and are some of the best LS heads ever made, far outflowing their cathedral cousins. This port design is also found on some 6.0L truck engines (and on the Pontiac G8 6.0L mill) as well as the Cadillac CTS-V and the LS9 in the Corvette ZR1. Due to an enlarged intake valve these heads use an offset rocker on the intake side. The major difference in the various heads are the types of valves used. The LS3 821 heads had hollow-stem valves, as did the LSA supercharged engine with the 863 heads. Heads for the LS9 used titanium intake valves like the LS7. The main difference between and LSA and LS9 head are the valves. The LSA heads also used a stronger rotocast A356-T6 alloy.
Common rectangular port production casting numbers:
716/821 LS3 heads – 68cc
863 ZL1/CTS-V LSA heads – thicker deck for boost – XXcc
823/5364/2716 L92 heads – 68cc
LS7 heads (452 castings), like the L92 heads, employ rectangular ports (a bit wider and shorter compared to the L92/LS3 ports). The 12-degree valve angle design (as opposed to the 15-degree valve angle used on all other LS engines) supports a straight-through airflow and utilizes 270cc intake ports. Also unique are that the ports and combustion chambers are CNC-ported straight from the factory. These heads only use LS7 intake manifolds or an aftermarket equivalent. These were also known for using titanium intake valves and sodium-filled exhaust valves, something previously unheard of in a pushrod V-8. They easily support over 600 hp naturally aspirated and the huge valves necessitate 4.125 or larger bores.
For the most part, all LS cranks are of the same design and have 2.10-inch rod and 2.56-inch main journal sizes. They are all iron with the exception of LS9, LS7, and LSA, which are forged steel. LS7 cranks have a 4.000-inch stroke while all the rest have a 3.622-inch stroke (except 4.8L cranks which are 3.270-inch). LS7 and LS9 (dry sump) cranks have a longer snout (about 1-inch) for their two-stage oil pumps, but can be used on wet-sump engines with the right parts and a modification or two. Another major difference between LS cranks is the reluctor wheel used for crank timing. Early ones will have a 24x wheel while later cranks will have a 58x wheel (shown). The reluctor wheels can be changed by any qualified machine shop.
Most LS rods are interchangeable and made from powdered metal. The exceptions would be LS9 (5.990-inch) and LS7 rods (6.067-inch), which are forged titanium (LS7/9 rods only work with LS7/9 pistons). The common length is 6.098-inch, except for 4.8L engines, which use 6.275-inch rods. LS7 rods have a unique bearing size that requires a different bearing than other LS rods. The weak point of all LS rods would be the rod bolts. This is especially true of pre-2000 engines. LS6 rod bolts (PN 11600158) would be an upgrade, and an even better option would be a set of ARP rod bolts. Remember that LS rods use a “cracked cap” design. That means each cap is an exact match to its rod, so never get them mixed up!
All LS engines, with the exception of the LS9, use hypereutectic aluminum pistons. An exception would be LSA pistons which are eutectic. Eutectic, with respect to piston material is the amount of silicon in the mix. 12-percent is considered eutectic and if more is present then it is hypereutectic. The LSA range is 11-13-percent silicon and the LS3 is 14.8- to 18-percent silicon. The biggest differences between the various pistons are the diameter, due to bore size changes, and those changes that effect compression ratio, such as a dish. Like cast pistons, they don’t like detonation and are good up to 550-600 hp, tops. Gen III pistons are held to the rod by a pressed in (interference fit) pin, so a machine shop will need to take them apart and reassemble. Gen IV (and Gen III LQ9) used “full floating” pins held in by locking rings.
|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)||3.78 x 3.62||270-295/315-335||9.5:1|
|L33||5.3L (327cid)||3.78 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)||3.78 x 3.62||300-320/320-340||9.9:1|
|LC9/LH8||5.3L (327cid)||3.78 x 3.62||300-320/320-335||9.5:1|
|LS7||7.0L (427cid)||4.125 x 4.000||505/470||11.0:1|
|L92||6.2L (376cid)||4.065 x 3.622||403/415||10.5:1|
|LS3||6.2L (376cid)||4.065 x 3.622||426-430/424||10.7:1|
|L99||6.2L (376cid)||4.065 x 3.622||400/410||10.7:1|
|LSA||6.2L (376cid)||4.065 x 3.622||556-580/551-556||9.1:1|
|LS9||6.2L (376cid)||4.065 x 3.622||638/604||9.1:1|