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What to Look for Among the Late Model GM Engine Nuggets
Words: Jeff Smith, Photos: Jeff Smith and General Motors
The increasingly popular engine sport for 21st Century hot rodders is locking in a sweet deal on a used LS engine to stab into an early muscle car. In order to spot a sweet deal, you have to be knowledgeable in the fine art of LS engine spotting. The world is full of self-proclaimed experts but when it comes to dropping your cash on a lump of iron or aluminum, the only way to know for sure is to be smarter than the seller. At first that may seem challenging since there are more than 40 different variations on the LS theme spanning its near 20-year history.
To make this process easier, we can group these engines into three distinct families. The original version is the Gen III that began with the LS1 in the 1997 Corvette, followed by the Gen IV upgrade in 2005. The most recent evolution is the Gen V direct injection (DI) variant. Other enthusiasts prefer to differentiate these powerplants by their cylinder head orientation with the early engines carrying cathedral ports supplanted later by rectangle-port heads. It’s the differences between these cousin engines that make choosing a good engine out of a pile of potential prospects the challenge and the fun of it all.
We’ll concentrate on only the engines from the ground zero Corvette LS1 and truck/SUV engines through the later model Gen IV. In 2014 the Corvette debuted the LT1 direct injection Gen V engine that was quickly followed in 2015 by the LT4 supercharged version. We will leave those Gen V’s for a later investigation. Trust us, there’s plenty of information to digest for the Gen III and IV engines so let’s get started.
We will focus on LS engines that are both plentiful and affordable. This includes the iron block truck engines – specifically the 4.8L, 5.3L, and 6.0L versions. If you’re on a strict budget but you’ve drank the Kool-Aid on the idea of an LS swap, consider the basic 5.3L iron block truck engine. At 326c.i., with a mild cam and headers, even a 100,000-mile engine can lay down 425-plus horsepower while maintaining its street manners. This can be accomplished with either a stock EFI truck manifold or with a carburetor and a dual plane intake. The 5.3L engine is the most widely-built LS engine and there are some aluminum block configurations (LC9 and LH6 starting in 2005) in various trucks and SUV Gen IV applications.
A few decades ago, it was a fact that small- and big-blocks were used up after 100,000 miles. But the LS family now delivers harder cylinder walls, electronic fuel control, and multi-coil ignition systems. Combined with superior lubricants, it’s not unusual to see 100,000-mile engines with minimal cylinder wall wear and occasionally the cylinder wall cross-hatch is still visible. This means that with a cam swap and cylinder head refresh it’s not unusual to make acceptable power from a resurrected LS engine. The displacement ranges from the smallest 4.8L to the big-dog 7.0L engines. We have personal experience with several well-used LS engines and all have performed well as street engines with untouched short blocks.
Gen III Cathedral Port Engines
The Gen III configuration began the LS legacy with a rear-mounted cam position sensor and a 24x wheel for the crank sensor. The most important feature of these engines however was the improved airflow from the cathedral-shaped intake ports. The vertically-oriented ports were designed to allow a direct shot for the fuel injector to the back side of the intake valve. Combined with a 15-degree valve angle, even the most pedestrian 4.8L truck head offers excellent flow potential compared to its small-block predecessor. In fact, even on a larger displacement engine, back-to-back dyno testing reveals that a good cathedral port head like the LS6 “243” or the LS2 “799” versions offer excellent torque potential for street engines compared to the rectangle port heads found on the Gen IV engines.
Among the most affordable Gen III engine swap candidates are the iron-block, 4.00-inch bore, 6.0L LQ4 / LQ9 truck and SUV variants. The LQ9 is the better of the two with its higher static 10:1 compression versus 9.5:1 for the LQ4. Both feature cathedral port heads and when you pump these engines up with even a mild cam swap they can easily make 450 lb-ft of torque and 450-plus horsepower. Within the affordable aluminum-block cathedral port Gen III versions, the LS6 is highly prized, but it is easy to duplicate this package with a simple cam and head swap on any LS1.
The LS2 that debuted in the 2005 Corvette is a Gen IV engine but think of it as a cross-over blend of Gens III and IV because it retained the cathedral shaped intake ports while benefitting from a larger 4.00-inch bore and displacement bump to 6.0L (364c.i.). Among the variations of this engine are the L76 /L77 engines used in the SSR pickup and Caprice police packages. On the induction side, the forums insist that the early LS6 Corvette/Camaro intake is the best cathedral port intake but dyno testing by our favorite Ninja dyno tester Richard Holdener has discovered that the factory Trailblazer SS cathedral port truck manifold makes more torque than the original truck manifolds while making more peak horsepower than its LS6 cousin. If you have the hood clearance, this manifold is the best choice and you can buy it brand new through RockAuto for under $150 (AC Delco PN 12580420).
Gen IV Rectangle Port Engines
The Gen IV version first appeared in conjunction with the 2005 LS2 Corvette employing multiple evolutionary changes for the LS family. Among the notable upgrades is electronic throttle, moving to a front-mounted cam sensor, and a higher resolution 58x crank trigger. This crank sensor conversion was necessary to enable the move to variable valve timing (VVT) and Active Fuel Management (AFM). The variable valve timing has become commonplace with late model engines for emissions reasons. AFM refers to the technique of using oil pressure to effectively drop four of the eight cylinders during light load situations to improve fuel mileage. This is accomplished by disabling intake valve lift within the hydraulic valve lifter, essentially creating a lost motion device where the lifter still travels up and down but the internal piston in the lifter does not transmit this movement to the pushrod. Many aftermarket performance applications seek to disable both the AFM and VVT functions in search of more power with a performance camshaft and other modifications.
The move to rectangle port heads is the most drastic modification within the GEN IV family for engines like the LS3, L92, L99, and others. The heads are fitted with extremely large cross-sectional, 260cc intake ports and 2.165-inch intake valves. These big valve heads can only be used on 4.00-inch bore or larger engines, which may be why GM pushed the LS3 to a larger 4.065-inch bore diameter. However, GM retained the 3.62-inch stroke, which pushed the displacement to 6.2L or 376c.i.
Following the 6.2 was the escalation to the 427c.i. LS7 that has received so much acclaim. In case you’re not familiar, the LS7 is unique for several reasons starting with its larger bore, longer stroke, and more compression. Because GM expected the engine to rev to 7,000 rpm, GM added lighter titanium connecting rods and intake valves. The heads, while appearing to be similar to the LS3, feature a unique intake port bolt pattern that requires its own intake manifold. The 12-degree valve angle and CNC-ported heads also sport 2.20-inch diameter intake valves. This was also the first LS production engine to employ a dry sump lubrication system. Since then, several Corvette versions also employ a dry sump system.
The L92 is a bit of a sleeper engine but it is an all-aluminum 6.2L that debuted in the ’07 Escalade, which makes it now almost 10 years old. As with most newer Gen IV’s, it spins both VVT and AFM but despite that complexity, it has great power potential with its rectangle port heads that could be rescued from a crashed or junked SUV.
Other notable rec-port engines within the Gen IV family are of course the two supercharged beasts. The LS9 ZR1 Corvette engine is the most widely known using a 2.3L Eaton supercharger to make a factory-rate 638 horsepower. It features a dry sump oiling system among features too numerous to outline here. This was followed by a similar supercharged LSA engine used in the 2009-newer Cadillac CTS-V lineup. This engine is more conservative with a smaller 1.9L supercharger that employs a more traditional wet sump lubrication system. While these engines will be rare and expensive in the used marketplace, they are available as new crate engines. The LSA is attractive at a somewhat affordable price. The E-ROD version on Summit currently goes for less than $13,000. When you consider what you’re getting for that price, (including a GM warranty) it’s tempting.
We’ve barely scratched the surface of the early lineup Gen III/IV engines, but this should be enough to start you on your path of finding the best engine for your next project. The LS family has found itself powering everything from swamp buggies and air boats to Bonneville record-holding engines and everything in between. All you have to do is decide which engine best fits your budget and your horsepower aspirations!
Cathedral Port Gen III Engines
| Engine | Displacement | Torque / HP | Bore/Stroke | Comp. | Block |
| LR4 | 4.8L (293ci) | 295 /285 | 3.78 / 3.27 | 9.5:1 | Iron |
| LM4/LM7 | 5.3L (326ci) | 335 / 295 | 3.78 / 3.62 | 9.5:1 | Iron |
| L33 | 5.3L (326ci) | 335 / 310 | 3.78 / 3.62 | 10.0:1 | Alum. |
| LS1 | 5.7L (344ci) | 350 / 350 | 3.89 / 3.62 | 10.2:1 | Alum. |
| LS6 | 5.7L (344ci) | 400 / 405 | 3.89 / 3.62 | 10.5:1 | Alum. |
| LS2 | 6.0L (364ci) | 400 / 400 | 4.00 / 3.62 | 10.9:1 | Alum. |
Rectangle Port Gen III Engines
| Engine | Displacement | Torque / HP | Bore/Stroke | Comp. | Block |
| LQ4 | 6.0L (364c.i.) | 370 / 325 | 4.00 / 3.62 | 9.5:1 | Iron |
| LQ9 | 6.0L (364c.i.) | 380 / 345 | 4.00 / 3.62 | 10.0:1 | Iron |
Rectangle Port Gen IV Engines
| Engine | Displacement | Torque / HP | Bore/Stroke | Comp. | Block |
| LS3 | 6.2L (376c.i.) | 428 / 430 | 4.065 / 3.62 | 10.7:1 | Alum. |
| L99 AFM | 6.2L (376c.i.) | 410 / 400 | 4.065 / 3.62 | 10.4:1 | Alum. |
| L92 | 6.2L (376c.i.) | 415 /403 | 4.065 / 3.62 | 10.5:1 | Alum. |
| LS7 | 7.0L (427c.i.) | 470 / 505 | 4.125 / 4.00 | 11.0:1 | Alum. |
| LS9 | 6.2L (376c.i.) | 604 / 638 | 4.065 / 3.62 | 9.1:1 | Alum. |
| LSA | 6.2L (376c.i.) | 551 / 556 | 4.065 / 3.62 | 9.1:1 | Alum. |
Popular Factory LS Cams
| Engine | Duration at 0.050 | Valve Lift | LSA | Cam Bolt |
| LM7 5.3L | 190 / 191 | 0.466 / 0.457 | 116 | 3 |
| LS1 early | 202 / 210 | 0.496/ 0.496 | 116 | 3 |
| LS1 late | 196 / 201 | 0.479 / 0.467 | 116 | 3 |
| LS6 | 204 / 218 | 0.550 / 0.550 | 117.5 | 3 |
| LS2 | 204 / 211 | 0.525 / 0.525 | 116 | 3* |
| LS3 | 204 / 211 | 0.551 / 0.525 | 117 | 1 |
| LS7 | 211 / 230 | 0.593 / 0.588 | 121 | 3 |
| LSA | 198 / 216 | 0.480 / 0.480 | 122.5 | 1 |
| LS9 | 211 /230 | 0.558 / 0.552 | 122.5 | 3 |
* Early 2005 –’06 LS2 cams were 3-bolt, 2007 – later LS2 converted to 1-bolt
