Gen III/Gen IV LS Engine: Specs, dimensions, and Engine History
We can easily trace the lineage of the current GM LS V8 powerplant all the way back to 1955 and the 265ci engine sitting in the engine compartment of a ’55 Bel Air. No other contemporary V8 engine can track its history back nearly 70 years. The Gen III LS engine began its domination of the domestic performance scene in 1997 with the introduction of the 5.7L LS engine in the Corvette followed quickly by a succession of smaller and larger variations on that original theme. While we could wax philosophic for paragraphs, it’s much more productive to get right into the heart of this engine family history. We have much to discuss.
Chevrolet prefers to debut its latest internal combustion accomplishments in the Corvette and quickly follow that with the rest of the line and so the fledgling 5.7L LS debuted in the new-for-1997 C5 Corvette. The powerplant was designed initially as an aluminum block, aluminum head engine, so strength was an integral part of the plan since power would be vastly improved over its Gen I predecessor.
In this story we break down the evolution of the LS engine in both Gen III and Gen IV configurations. The Gen III engines were the firstborn from the original LS1 in 1997 through 2002. These engines used a 24x crankshaft trigger wheel and a cam sensor mounted at the rear of the camshaft. Roughly in 2003, GM upgraded the LS into its Gen IV configuration with a number of changes. The upgrades included a 58x crank trigger wheel with the cam sensor moved to the timing chain cover.
The LS was eventually delivered in multiple cubic inch configurations that did not stray far from its ancestral roots. The LS 4.8L (293ci) is nestled near the Gen I 283ci, the 5.3L LS truck engine is close to the venerable 327 at 325ci, and the 5.7L LS is kissing-cousins-close to the classic 350ci small-block. The 6.2L (376ci) could be considered approaching the 1970 400ci Mouse motor and then GM broke the mold to build a 427ci small-block LS with the LS7 engine.
These engines also employ a dizzying number of regular production option (RPO) designators like LS1, LS2, LS3, LM7, LQ4, LS6, and LS7 – among many more. This RPO-speak expands into pure alphabet versions like the LSA which is a supercharged Gen IV 6.2L engine. A few of these RPO’s are retreads from previous generations. For example, the 2006 LS6 engine shares it’s RPO with a 1970 big-block 454 Chevelle engine.
The deep skirt block is the first obvious point of departure from its small-block roots. This deep skirt extends past the crankshaft centerline, allowing for horizontal cross-bolted main caps. Other changes include a cast aluminum oil pan and front and rear covers instead of thin steel stampings. This design also paid careful attention to minimizing leak paths, a persistent problem with earlier small-blocks. Bore spacing was maintained to the same dimension as earlier small-blocks at 4.400-inches in an attempt to minimize its length.
As the LS family expanded its displacement footprint, horsepower expectations grew almost overnight. Keep in mind that engine rating systems have long since changed from the old gross horsepower ratings of the 1960s - replaced by ever-stringent ways of both measuring and correcting horsepower. So a 350 horsepower rating from an L79 1966 Chevy II for example would produce far less than its rated power if tested under current test standards and would appear weak compared to a 1997 350 horsepower LS1.
All engines are air pumps and major revisions were enacted that radically enhanced power. Much of this newfound power is attributable to the significantly improved flow potential of the LS family of cylinder heads. Much of this is due to a revised 15-degree valve angle (compared to 23 degrees) but also to drastically improved combustion chambers and a valvetrain with hydraulic roller cam and stock 1.7:1 rocker ratio compared to the traditional small-block’s 1.5:1 effort. The intake system also enjoyed major improvements with composite intakes and large diameter throttle bodies. Even something as mundane as the exhaust manifolds are far better than earlier log manifolds.
As the LS evolved it also integrated many modern ideas that in the ‘60s would not have even been dreamt as possible. For example, GM soon added variable valve timing (VVT) to the LS package where computer-controlled hydraulic pressure can move the camshaft through as much as 60 degrees of potential advance or retard movement. Advancing the cam timing at lower engine speeds creates additional torque while retarding the cam at high speed can improve horsepower.
What soon followed was what GM calls AFM or Active Fuel Management which is a catchy acronym for removing four cylinders from the combustion process during light load highway cruising applications. This system was eventually upgraded to Dynamic Fuel Management (DFM) which expanded the cylinder dropping process to all cylinders and allowed a V8 to run on as few as two or three cylinders.
Another major departure was the LS permanently altered the traditional firing order. The new order is 1-8-7-2-6-5-4-3. The cylinder numbering sequence is still the same with odd cylinders on the driver side and even on the passenger bank. If you study this new firing order, you can see that this merely reshuffles the pairings of 1 -8, 4- 3, 6- 5, and 7-2.
To skin this LS orange and get at its juicier details, let’s start with the cylinder block and work all the way through the entire assembly. We’ll place a little added attention on the cylinder heads as that is where the secrets to real horsepower can be found
The LS is really an extension of the original small-block Chevy from 1955. This is based on GM retaining both the small-block’s 4.40-inch bore spacing along with the Gen I’s bellhousing bolt pattern (with a slight change). Excluding a couple of minor exceptions like rod bearings and lifter diameter, The Gen III is a whole new animal.
Engineers began their on-screen redesign assuming the LS would use an aluminum cylinder block. Later truck engines were produced in high-strength cast iron, but the block was always intended as an alloy casting with cast-in iron cylinder sleeves. The initial LS1 was configured with a smallish 3.89-inch bore but this quickly grew to 4.065 and eventually up to a 4.125-inch diameter for the LS7.
B eyond bore size, the real change was a move to what is called a deep skirt block where the oil pan rail is extended below the crankshaft centerline. This places support alongside the main caps using smaller, cross-bolted fasteners in addition to the four main cap bolts. Another major change was moving the thrust bearing from the tail of the crankshaft to the center main position that contributes to less deflection in the crankshaft.
The Gen I small-block employed 17 bolts to seal the head to the block while the Gen III version cut that count to just 10. Early LS blocks used staggered-length head bolts while later blocks equalized the bolt lengths. LS engines also use torque-to-yield, one-time use head bolts in an effort to equalize load on the gasket that is now a multi-layered steel (MLS) design that is far superior to older composition gaskets.
The new LS block also upgraded to a much larger 55mm (2.165-inch) diameter camshaft core. We’ll detail the reasons for this in our camshaft section but a larger steel core creates a much more stable platform for the valvetrain.
In the old small-block days, GM offered a new crank with almost any new displacement. The Gen III/IV engines minimized stroke length changes while offering multiple displacements. The smallish 4.8L engine use a specific 3.26-inch stroke while the 5.3L, 5.7L, 6.0L and even the 6.2L engines all spin a 3.622-inch factory arm. It’s also possible to interchange these cranks to allow using a 5.3L crank in a 6.0L block and balance will be close. GM achieved this by making its smaller bore pistons heavier so that balance between all the various displacements would not require massive machining.
We’ll get into more detail on the Gen IV applications at a later point but a significant differentiation occurred when the LS2 debuted in 2006 as Gen IV. The crank reluctor wheel changed to a 58x count instead of the previous 24x. The numbers reflect the number of teeth (x indicates 2 missing teeth) which means ECU’s for these engines do not interchange. Lingenfelter Performance Engineering does offer electronic interchange boxes that will allow some crossover if that is of interest.
Nearly all Gen III/IV cranks are nodular cast iron although there are a few exceptions. Gen IV engines like the 427ci LS7 and the supercharged LSA and LS9 engines all increase durability with a forged crankshaft because of a combination of high specific output and rpm. The LSA and LS9 cranks also employ an 8-bolt crankshaft flange as opposed to the more common 6-bolt arrangement. The LS7 crank is different not just because of its 4.00-inch stroke, but also because of a longer snout that accommodates the dry sump pump oiling system first employed on the LS7.
Unlike the traditional small-block that eventually witnessed three different main bearing journal sizes through its lifespan, all LS engines are consistent with main journals at 2.559-inches with a rod journal that is a carry-over from the late small-block Chevy at essentially 2.100-inch. In fact, the small-block and LS use the same rod bearing. That makes for an easy conversation starter at parties if you are at a loss for words.
With varying bore sizes, strokes, and rod lengths, it would take a small anthology to list all the different piston configurations, so we’ll stick to the more general information. Most, but not all, LS engines were configured with hypereutectic pistons using a dry, anti-friction coating on the skirts. The standard wrist pin diameter is slightly larger at 0.940-inch compared to the traditional small-block’s 0.927. This is important if you decide to change to a set of aftermarket pistons or connecting rods as these new performance parts come in both wrist pin sizes.
Perhaps the most important change in piston design was the move to a 1.5mm / 1.5mm / 3.0mm ring package. To make this easier to understand, let’s convert these ring thicknesses to a digital format. A standard small-block Chevy ring from 1970 was 5/64-inch ((0.078). A performance ring thickness is 1/16-inch (0.0625) while a 1.5mm (0.0585) is significantly thinner and barely more than 0.043-inch rings that used to be cutting edge in drag racing. The LS7 moved to a 1.2mm / 1.2mm / 2.0mm ring package and the trend appears to move even thinner.
While most enthusiasts think these thinner rings were aimed at performance, but in this case GM chose these anorexic rings to reduce friction, improve fuel economy and also boost power slightly. The real place where friction was reduced is with the thinner 3.0mm (0.187) oil control ring package. This ring pack creates substantially less friction (and therefore fees up even more horsepower) especially compared to the old 3/16 (0.1875) oil rings while still maintaining good oil control.
To improve combustion efficiency, most LS pistons are a pure flat top design, but there are exceptions. For example, early Gen III 6.0L truck engines use the same combustion chamber. A dished piston was used with lower compression LQ4 engines while higher compression LQ9 employed a flat top. Later Gen IV supercharged engines like the LSA and LS9 use dished pistons to reduce the static compression ratio. The LSA engine engines in the Cadillac CTS-V were fitted with a hypereutectic piston while the Corvette LS9 enjoyed a 4032 alloy forged piston.
Another area where the LS family of engines diverged from the small-block norm is with connecting rods. While the new LS rod is forged, it uses a different, powdered metal process. For production and mild performance engine use, these are acceptable, but they can suffer failures when abused by high engine speeds.
One reason to employ the powdered metal design is to take advantage of what is called fractured cap technology. When a traditional rod is forged, it is created in one piece and the cap is removed with a saw. Powdered metal rods are also forged in one piece but then the cap is essentially broken off, leaving a fractured area at the break that creates a very accurate way to locate the cap to the main body of the rod.
Unfortunately, fractured caps do not allow the big end to be traditionally resized since the cap cannot be trimmed and then the big end honed to the proper size. This is one place where if you are building a performance LS engine that it is worth the investment into a true 4340 forged steel connecting rod.
The most popular LS rod length is 6.098-inches but there are other lengths for certain special applications. The 4.8L LS uses a shorter 3.26-inch stroke. To compensate for this reduced stroke, GM lengthened the rod to 6.275-inch. If you do the math, you’ll see that this additional rod length is only about half of the difference in stroke, the rest is handled with a taller compression height in the piston.
Most LS enthusiasts are aware that the high-revving 427ci LS7 Corvette engine enjoyed the addition of a special titanium connecting rod. Not only is it titanium, making it both strong and light, but the length is also shorter than a standard LS rod at 6.067-inch and features a bushed small end for a full floating pin. While this might sound like a potentially desirable upgrade, the LS 7 rods have a narrowed wrist pin end that will require a custom piston. For this and other reasons, it’s less expensive and frankly a better idea to upgrade to an aftermarket forged 4340 steel rod.
While the floating pin is part of the LS7 package, GM began the process of converting all LS engines over to a full floating wrist pin in roughly 2005 which means you must be aware of this when upgrading early or late engines with performance parts such as a bushed connecting rod. This will need pistons with retaining clips to make the conversion work.
Starting with the basics, all LS engines use a 55mm core steel camshaft. The journal diameter is significantly larger than the stock small-block Chevy (2.165-inches vs. 1.875) which is a move in the right direction. A larger journal diameter is much stronger and more rpm-stable which also allows a larger base circle which also increases durability.
As you might expect, production camshafts offer rather conservative lift and duration numbers along with very wide lobe separation angles (LSA). A typical aftermarket performance camshaft will use an LSA of 110-114 degrees while a stock LS cam is between 116 and 122 degrees. This wider LSA creates a much smoother idle quality which is something that all production engines strive to achieve.
The camshaft is driven by a typical gear and single-row chain arrangement at the front of the engine. The Gen III engines placed the cam sensor at the rear of the camshaft. But with the introduction of the LS2, the cam sensor migrated to the front of the engine on the front cover. Over this same period, the camshaft retaining arrangement also evolved from its original 3-bolt to a single bolt. This obviously changes the cam gear drive and because of other subtle changes, this created a total of four different cam drive configurations that include both the 3-bolt and single bolt drives along with evolutions for cam sensor treatments.
All these changes mean that upgrading the camshaft has become a somewhat more complex decision-making process because you will need to know the engine’s vintage and application to ensure the proper cam core is selected. For example, a single-bolt cam won’t work on a Gen III engine because the cam sensor trigger wheel is not used on the newer 1-bolt cam gear. You could still do this but would require moving the cam sensor to the front of the engine with LS2 style parts. The point is that the ease of mixing and matching parts that everyone is used to with the small-block Chevy is not quite as simple when it comes to the Gen III/IV engines. There are more rules to follow.
As you can imagine, there is a huge spread of available lift and duration choices starting with the very short duration cams for trucks and SUVs transitioning all the way up to the LS7 camshaft that features some rather aggressive lift and duration numbers. But before you drop your cash on retro-fitting an LS7 cam to your 5.3L truck engine, be aware that while 211/230 degrees at 0.050 with 0.550-inch lift numbers sound impressive and are probably near 20 degrees more duration than your stock 5.3L cam, you may be disappointed with the results with regard to low-speed throttle response.
As just one example, if you want to experience a mild improvement with a stock factory cam for a 5.3L or even a much larger 6.0L truck engine, the factory LS6 cam would be a far better choice. The LS6’s cam offers similar valve lift numbers in the 0.550-inch lift range compared to the LS7 cam, but enjoys shorter duration at 0.050 and a narrower LSA – both of which are still improvements over the stock LQ4 cam. This would work very well in a truck, SUV, or street car engine swap while still delivering a solid power increase along with OEM idle quality.
All production LS engines are equipped with hydraulic roller lifters operating a very stable valvetrain. The overall engineering concept was aimed at stiffening the valvetrain while minimizing mass. To accomplish this, GM developed an excellent investment cast steel 1.7:1 rocker arm with a needle bearing pivot that reduces friction and lowers oil temperature.
To make the engine easier to assemble, GM designed what is called a net lash system where instead of a rocker using a single adjustable stud, the LS rocker is bolted directly to the cylinder head. Because the distance from the rocker pushrod cup to the lifter body is a fixed distance, pushrod length is used to establish the desired lifter preload. The stock pushrod length on a non-AFM LS engine is 7.40-inches, which adequately preloads the lifter by roughly 0.050 to 0.060-inch.
A now-common advancement in valvetrain stability included what are now called beehive valve springs. The description is accurate as the spring tapers as it approaches the top, creating a smaller and lighter retainer. By reducing the weight of the top half of the spring, the beehive increases the spring’s ability to control the valve at higher engine speeds. Therefore the spring is more stable over a wider rpm range, contributing to more power and increased durability.
Variable Valve Timing (VVT) became available with certain Gen IV engines, allowing an amazing 62 degrees of potential cam movement over the entire range of engine operation. Part of the Gen IV package included a faster and more powerful ECU that controls a hydraulic servo that advances or retard the cam based on engine speed and load (engines equipped with VVT). The ECU advances the cam at idle and low rpm engine operation to improve low-speed torque and throttle response. As rpm and load increase, the ECU will begin to retard the camshaft to enhance peak power.
This system works seamlessly and is another reason these engines make such outstanding power at low engine speeds relative to their displacement. A minor detraction is that VVT engines are limited in terms of camshaft upgrades because with a longer duration camshaft, a major position “swing” can cause piston-to-valve interference. Mild performance cam changes can be accomplished without limiting VVT operation but more aggressive cams will demand either a limiter that reduces the degrees of operation or complete VVT elimination.
Another step in the evolution of the LS was the integration of what GM calls Active Fuel Management (AFM) that is often been called displacement-on-demand. In the Gen IV version of AFM, four cylinders (1, 4, 6, and 7) are selected to be “dropped” during light load, highway cruising situations. This turns a 6.0L V8 essentially into a 3.0L V4 during AFM operation and the conversion in and out of AFM is seamless to the driver.
This cylinder deactivation is accomplished by using special, spring-loaded lifters that when signaled by the ECU uses hydraulic oil pressure to nullify valve action on both the intake and exhaust valves on the affected cylinders. The lifter continues to follow the cam lobe, but by disengaging the lifter, it becomes what can be described as a lost motion device. The lifter travels up and down, but the small piston inside the lifter does not impart lift to the pushrod so it does not move.
In many cases, older AFM LS engines experience drivability and performance problems when debris in the system clogs the activation passages in the lifters. This is often caused not because of faulty design but instead because of abused oil drain intervals that create sludge in the system. Many engine swappers deal with this by eliminating AFM.
The simplest way to classify the LS family of heads is into two categories: early cathedral and later rectangle port heads. These refer to the shape of the intake port. The Gen III cathedral port heads get their moniker from the tapered upper portion of the port that allows the fuel injector to aim directly at the back side of the intake valve. Oddly, the earliest truck engines for the first two years were equipped with iron castings, but GM quickly stopped that practice and all subsequent LS engines use alloy heads.
The focus on increased LS power and torque really centers on improving airflow. Much of this LS family’s drastic airflow increase can be attributed as much to a simple adjustment in valve angle. The traditional small-block employed a 23-degree intake valve, which is the relationship of the valve face to the engine’s deck surface. Racers and internal combustion enthusiasts have known for decades that a more vertical valve angle to the deck surface and matching that with a raised intake port will minimize the airflow direction change which will enhance airflow through the port.
GM engineers were well aware of this and bumped the original LS intake valve angle to an airflow-enhancing 15 degrees. So when someone tries to convince you that the small-block Chevy can run with the LS, numbers tell a different story.
The initial cathedral port heads came in several orientations with slightly different valve sizes and combustion chamber volumes. The original 5.7L LS1 and later hopped up LS6 used a head that still has value for small displacement engine builders using a 2.00-inch intake and a 1.55-inch exhaust. The 4.8L and 5.3L engines shared a tighter chamber with a smaller1.89-inch intake valve. Six liter Gen III truck engines employed the same intake valve diameter as the LS1.
Chamber sizes also vary greatly. The LS6 used a 65cc chamber to raise compression slightly while the smaller 4.8L and 5.3L truck engines were fitted with a 61cc chamber to maintain compression. The 6.0L truck engines enjoyed a larger bore, so to maintain a 9.5:1 compression these heads used 70-71cc chambers. A quick way to increase performance on a mild street 6.0L truck engine is to have a machine shop add a larger 2.00-inch LS1 valve to a set of 5.3L LM7 heads. The combination of the smaller chamber and larger intake valve is worth both added torque horsepower and improved drivability.
The headline news with the upgrade to the Gen IV package centered most attention around the massive rectangle intake ports, equally broad intake valve size and the almost unbelievable flow numbers that followed. These huge intake ports took the intake port volume from roughly 200-210cc’s to a portly 260cc. While the volume rose dramatically, so did the airflow.
Let’s take the LS3 or L92 head as an example. This head features an intake port volume of 261cc’s, an intake valve diameter of 2.165 coupled with a 1.59-inch exhaust valve. A stock as-cast intake port can flow upwards of 326 cfm at 0.600-inch valve lift even though production camshafts rarely reach beyond 0.550-inch lift. Compare that 325+ cfm number to a cathedral port that measures around 260 cfm and you can see why enthusiasts get excited. These huge ports do tend to slow the inlet velocity at lower engines speeds which would seem counter-productive compared to cathedral ports with a much smaller cross-sectional area.
Airflow is generally king but there are limitations. The large 2.165-inch intake requires a minimum bore size of 4.00 inches just so the valve will clear the edge of the cylinder. A larger bore, like 4.065-inch will always contribute to increasing airflow and power potential.
But even the LS3 head is not the pinnacle of production rectangle port evolution for a normally aspirated engine. GM achieved that with the LS7 head moving the intake valve angle even steeper to 12 degrees and increasing the bore size to 4.125-inch. The intake valve on these heads is an impressive titanium alloy to reduce weight since the valve size expanded to an unprecedented 2.20-inch. Airflow obviously took a giant leap forward, surpassing 370 cfm at 0.670-inch lift.
Most of this attention has been on the intake ports, but the exhaust side is also very much improved. While everybody tends to focus on the inlet side of the airflow chart, you can’t make power at high rpm if the exhaust gas struggles to leave the chamber. The exhaust on these heads can flow in excess of 210 cfm at 0.600-inch lift while the cathedrals are limited to the mid-180 cfm area.
While it may seem that with the massive flow potential, the rec port heads are the way to go. But airflow is not the entire answer as velocity also plays a part. For a mild normally aspirated street engine, cathedral port heads can be very rewarding. As an example, 550-plus horsepower is easily achievable with an iron Gen III 6.0L using aftermarket cathedral port heads and a strong camshaft on pump gas at 6,500 rpm.
For supercharged engines, the rec ports are the way to go as they represent less restriction to airflow. With a large intake port, a given supercharger will flow more air at less backpressure (boost) compared to a set of cathedral port heads. That’s one reason why the boost levels on the supercharged LS engines tend to be low. The blower doesn’t have to work as hard to push the air into the cylinders.
The most noteworthy evolution in the LS lubrication system was to relocate the oil pump over the snout of the crankshaft just in front of the cam drive assembly. The first thing this does is spin the oil pump at engine speed versus driving if off the camshaft at half engine speed.
Relocating the oil pump on the front of the engine required a much longer oil pump pickup tube since all LS engines still use a rear sump oil pan. This drastically lengthens the distance from the sump to the oil pump. This isn’t a huge problem, but does sometimes cause oil pressure issues for brand new engines when the oil pump is not primed. This may require external priming from an outside pressure source like a small pre-luber.
The LS oiling system does emulate its small-block Chevy cousin in that once oil is pressurized and exits the filter, it feeds two large galleries that direct oil first to the lifters. Once the lifters are pressurized, oil is directed down through holes in the main webs where the main and rod bearings are lubricated. Another less significant change is that all LS oil pans are cast aluminum and designed to be an integral part of the block as opposed to merely stamped steel appendages. There are multiple LS engine oil pan configurations depending upon body style. The truck pans tend to be very deep while passenger car pans will be in various different configurations.
For engine swappers, Holley makes a couple of cast aluminum pans that create crossmember and steering linkage clearance. One advantage to these aftermarket pans is they retain the factory oil filter orientation. Some sheetmetal pans require a remote oil filter location that can be both problematic in tight engine compartments and also significantly add to the overall expense.
While nearly all factory LS engines employ a wet sump orientation, the LS7 and some subsequent performance engines like the LT4 use what is called a semi-dry sump system. In a true dry sump, multiple scavenge stages pull all the oil from the pan and lifter valley. For the LS7 engine, it pulls oil from the oil pan and using a single scavenge side of a two-stage pump. This side then pushes the oil into a separate tank located alongside the engine.
The whole point of a dry sump is to remove as much oil from the engine as possible and store it in a separate tank that will always have oil available to the inlet of side of the pressure pump. The pressure side of the two-stage LS7 pump pulls oil from the tank, pressurizes like any normal pump and then pushes the oil through the engine where it lubricates and eventually returns to the sump where the process repeats.
Obviously, this system is much more complex than a standard wet sump and requires multiple external plumbing and fittings. To accommodate the two-stage LS7 pump, the LS7 crankshaft snout is longer than normal. Because of the crank snout and other components, the LS7’s dry sump cannot be easily added to factory LS wet sump engines.
Cathedral port cylinder heads on the Gen III engines require a specific cathedral port intake manifold that is not interchangeable with later rectangle port intakes. The cathedral port engines were generally fitted with a 3-bolt throttle body measuring between 78 and 90mm. From the earliest 5.7L LS1, Corvettes and electronic throttle control (ETC) were paired together, but truck engines and the Camaro were slower to adopt this improvement.
In roughly 2005, when GM upgraded to the LS2 Gen IV configuration, ETC became standard with larger, four-bolt throttle bodies. ETC also improved and was integrated into the faster and far more powerful ECU that also controlled VVT and AFM. ETC also requires an electronic throttle pedal. This becomes a separate component that must be ordered if you are considering one of Chevrolet Performance’s crate engine packages or perhaps one of the emissions-compatible E-ROD engines like the 6.2L LS3.
All LS engines use a composite intake manifold and there are several variations on this theme. Truck engines generally employ a taller manifold to accommodate longer runners that emphasize low-and mid-range torque for hauling heavy loads. Passenger car manifolds are much lower in profile with shorter runner lengths that offer more top-end power potential. In both cases, Gen III manifolds use three-bolt throttle bodies while the Gen IV versions use larger diameter four-bolt throttle bodies. As an example of size, the 1997 5.7L LS1 was fitted with a 75mm electronic throttle while it’s later and larger 6.2L cousin breathes through a 90mm throttle.
Common sense dictates that the larger, Gen IV rectangle port intakes will not directly interchange with earlier cathedral port head engines and vice versa. However, several aftermarket companies do make billet aluminum adapter plates that will allow running an LS3 manifold on an LS engine with cathedral port heads.
Among the popular factory intake manifold swaps for cathedral port Gen III engines is the LS6 intake which flows slightly better than the original LS1 although now becoming difficult to find as a used part. The LS2 intake is also a typical upgrade. What is less well known is that GM built a series of performance applications that included what became known as the Trailblazer SS from 2006 –‘09.
This 6.0L engine enjoyed a slightly more aggressive cam, good 243/799 heads, and an excellent intake manifold. Of interest for budget manifold swappers is that while this Trailblazer SS intake is tall and a bit bulky in appearance, it makes more torque than the cathedral port truck manifolds and more horsepower than the LS6.
The horsepower escalation race received a major boost with the addition of a couple of factory-originated supercharger packages. The milder of the two appeared in the 6.2L ZL1 Camaro labeled as the LSA using an Eaton, 1.9L roots style supercharger blowing through an integrated intercooler located underneath the supercharger. With a 2.6:1 drive ratio, the stock blower was limited to 9 psi. This same blower package was also available making 556 horsepower in the Cadillac CTS-V sedan.
The big dog supercharged engine is dubbed the 6.2L LS9 and blessed with a much larger Eaton 2.3L four-lobe rotor package that can make an impressive 10.5 psi boost with a similar packaging arrangement of an intercooler located below the blower. With a larger blower, more boost and a more aggressive cam, the LS9 is rated at 638 horsepower and 604 lb-ft of torque. With minor tweaks, this engine can easily push the power up to 750 horsepower.
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It’s no surprise that the LS Gen III and IV versions enjoy such success in the aftermarket. Even in pure stock form, these engines are light, easy to work on, don’t leak and – best of all – make outstanding power. What’s not to like? And since millions of these engines have been built, their numbers ensure their affordability. The only question is which engine to choose. It’s a good problem to have.
|Displacement (cubic inches)||Bore||Stroke||Block Material|
|5.3L (325)||3.78||3.62||Iron (some castings are aluminum)|
|6.0L (364)||4.00||3.62||Iron, Aluminum|
|HP @ RPM||TQ @ RPM|
|LR4||4.8||III||Iron||9.5:1||285 @ 5,200||295 @ 4,000|
|LM4/LM7||5.3||III||Iron||9.5:1||310 @ 5,300||325 @ 4,000|
|LS1||5.7||III||Aluminum||10.2:1||350 @ 5,600||365 @ 4,400|
|LS6||5.7||III||Aluminum||10.5:1||405 @ 6,000||400 @ 4,800|
|LQ4||6.0||III||Iron||9.4:1||325 @ 5,200||370 @ 4,400|
|LQ9||6.0||III||Iron||10.0:1||345 @ 5,200||380 @ 4,000|
|L76 AFM||6.0||IV||Aluminum||10.9:1||367 @ 5,400||375 @ 4,400|
|L99 AFM||6.2||IV||Aluminum||10.4:1||400 @ 5,900||410 @ 4,300|
|LS2||6.0||IV||Aluminum||10.9:1||400 @ 6,000||400 @ 4,400|
|LS3||6.2||IV||Aluminum||10.7:1||436 @ 5,900||428 @ 4,600|
|L94 AFM||6.2||IV||Aluminum||10.4:1||403 @ 5,700||417 @ 4,300|
|LSA *||6.2||IV||Aluminum||9.1:1||580 @ 6,100||556 @ 3,800|
|LS9 *||6.2||IV||Aluminum||9.1:1||638 @ 6,500||604 @ 3,800|
|LS7||7.0||IV||Aluminum||11.0:1||505 @ 6,300||470 @ 4,800|
- Note: These engines are supercharged. The LSA uses a 1.9L Eaton supercharger, while the LS9 employs the larger 2.3L Eaton supercharger.
|5.7L LS6 (2002)||204||218||0.551||0.547||117.5|
Factory Cylinder Head Casting Numbers
Gen III/IV Specifications
|Block||Deep skirt block with cross-bolted mains|
|Block Weight (bare)||Aluminum LS2 - 106 lbs.|
Iron LQ4 - 216 lbs.
Iron LSX race block - 230 lbs.
|Engine Weight||390 lbs (aluminum block, approx.)|
|Bore Spacing||4.40 inches|
|Deck Height||9.240 inches|
|Cylinder Offset||0.0949 inches, left bank forward|
|Main Journals||5, with thrust at #3|
|Main Journal Housing Diameter||2.751 inches|
|Crankshaft||Nodular iron (LSA, LS9 and LS7 are forged steel)|
|Crankshaft Reluctor||Gen III - 24x / Gen IV - 58x|
|Crankshaft Stroke||4.8L - 3.26|
5.3L and 6.0L - 3.622
7.0L - 4.00
|Crankshaft Main Journal Dia.||2.559 nominal|
|Crankshaft Rod Journal Dia.||2.0995 nominal|
|Connecting Rod Length||4.8L - 6.275|
LS7 Titanium - 6.064
LS9 Titanium - 5.998
All Others - 6.098
|Camshaft Journal Dia.||55mm (2.163 in.) / Compare to SBC = 1.868|
|Lifters||Hydraulic roller, 0.842 inch diameter|
|Rocker Arm Ratio||1.7:1, except:|
LS7 - 1.8:1
|Hydraulic Lash Adjustment||Net lash design - lifter preload set by pushrod length|
|Piston||Cast aluminum, except:|
LS9 - OEM forged pistons
|Piston Compression Height||LS1 - 1.340|
|Piston Ring Package||1.5mm, 1.5mm, 3.0mm, except:|
LS7 and others: 1.2mm,1.2mm, 2.0mm
|Piston Pin Diameter||0.945 inches, except:|
LS9 - 0.985 inches
|Piston Deck Height||Nominal 0.008 inch above deck|
|Oil Pump||Crankshaft-mounted gerotor design|
|Cylinder Head Material||Aluminum 356 T6, except:|
1998-99 LQ4 - Iron
|Cylinder Head Port Design||Gen III - Cathedral|
Gen IV - Rectangular
|Intake Manifold||One-piece composite|
|Throttle Body Diameter||Gen III - 78mm|
Gen IV - 90mm
Gen III Cable and ETC
Gen IV ETC exclusively
|Fuel Pressure||58 PSI|
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