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Gen III/IV LS Engine ID Guide

10/4/2021
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The OG Chevy Small Block Makes Way for The New Kid on The Block

The small block Chevy has been the predominant engine swap candidate from about a week after the first engine block casting cooled in the mid-1950s. This little gem of an engine has seen displacement from 262 to 400 cubic inches in its 50 plus years of existence. Eventually it was replaced by GM’s new for 1997 Gen III LS engine, first seen in the 1997 model year Corvette as the LS1 where it replaced the Gen II LT1 as the Corvette’s standard engine.

The Venerable Gen I Small Block Chevy, As Seen In A '32 Ford

You wouldn’t know it by the proliferation of LS engine swaps today, but the old-school small block Chevy used to be THE engine to swap. Today though things are a bit different. It’s still very much a GM-centric swap world, but the traditional Gen I (and Gen II) small block swap has given way to a huge inrush of LS swaps thanks to many manufacturers providing easy swap bits like swap mounts, conversion headers, bolt-in crossmembers, low-profile oil pans, and more. The Gen III/Gen IV LS swap is now easier than ever to accomplish thanks to these efforts, but what has made the LS so popular that these manufacturers ponied up the resources and financial backing to make all these parts?

What Makes the LS Engine So Good?

While the LS engine launched as a 5.7L/350ci engine with the LS1, it is far from the 350 small block Chevys of old. This all-new engine design may share displacement with the old Gen I and Gen II small block Chevy, but even it’s displacement comes at a different bore and stroke. The 5.7L LS1 uses a 3.89-inch bore and 3.62-inch stroke compared to the original 350’s 4.00-inch bore and 3.48-inch stroke). So, while both engines are “over square” when it comes to bore and stroke, the LS loses a little in piston diameter but makes up for it in stroke length. This allows the engine to remain compact, one of its top swap traits, yet still provide plenty of torque and high rpm ability.

The LS Engine Family Uses A Deep Skirt Block With Six-Bolt Main Caps For Strength

It’s not all about piston size and rod length either (though the LS engine family has several iterations of both). The LS engine, available in both aluminum and cast-iron block configurations, is a deep skirt engine block design, meaning the cylinder block side walls completely cover the crankshaft’s profile. In addition to this deep skirt design the crankshaft is supported by six bolts per main cap. Four in the traditional location and two through the side of the block’s skirt/oil pan rail area. This increases block rigidity by tying both sides of the block together through the main caps and holds the bearing caps in place to better resist the forces of the piston and connecting rod acting upon it.

The LS engine family further distances itself from the traditional small block Chevy with a 15-degree valve angle using high-flow cylinder heads and a long-runner style intake manifold, all working together to increase engine airflow for more power, torque, and efficiency. Additionally, the LS platform uses production 1.7:1 ratio roller rockers with a low moment of inertia design. This contributes to the LS’s valvetrain stability at high rpm.

The LS Engine Family Uses A Coil-Near-Plug Distributorless Ignition

Lastly, and one this being one of the biggest visual changes, is the move to a distributorless ignition system on the LS platform. The LS’s coil-near-plug system places individual coils mounted on the valve covers directly above each spark plug location with a short spark plug wire. This system is fully computer controlled and uses several sensors to properly fire each individual coil, which provides for more accurate spark control and higher rpm abilities. Now we know some of you might be raising your hand to say the LT1 didn’t have a distributor either. Technically not at the rear of the intake like a Gen I small block, but the Opti-Spark system behind the water pump and driven by the nose of the camshaft is indeed a distributor, with a serviceable cap and rotor system. So, the LS is GM’s first truly distributorless V8 offering.

What Vehicles Have LS Engines?

You can find the LS engine in many GM family cars and trucks. Below we break down the model years with some of the more popular LS engines you will find in them. We provide more detailed information on the full list of available LS engines, including cylinder head casting codes, VIN codes, displacement, and more in our giant Gen III/Gen IV LS Engine ID Guide chart.

Speedway Motors' LS Engine ID Guide Chart

When checking out a vehicle at a salvage yard you can use the vehicle's Service Parts Identification label to confirm the factory installed engine by VIN code (8th digit) or the RPO code of the engine. The Service Parts Identification label is usually found in the vehicle's glove box. 2018 and newer models moved to a QR code on the door jamb's certification label that you will have to scan with your smart phone QR reader/camera app in order to obtain the VIN and RPO data.

The Vehicle's Service Parts Identification Label Will Have The VIN Digit and Engine RPO Code (Circled) To Confirm Engine Application

Gen III LS Engine Car Applications

  • 1997 to 2004 Corvette, 1998 to 2002 Camaro & Firebird, 2004 GTO: 5.7L LS1
  • 2001-2004 Corvette, 2004-2005 Cadillac CTS-V: 5.7L LS6

Gen III LS Engine Truck Applications:

  • 1999-2007 Silverado 1500/Sierra 1500 and SUV applications: 4.8L LR4 and 5.3L LM7
  • 1999-2007 Silverado 2500/Sierra 2500 3/4-ton: 6.0L LQ4

Notable differences from Gen III car applications:

  • Taller truck style intake manifold
  • Deeper sump truck style oil pan
  • Cast iron engine block
  • Cast iron heads on 1999 and 2000 LQ4 6.0L engines (373 and 873 head casting numbers)

Desirable Gen III Truck Engines:

  • LM4 and L33 5.3L engines which have an aluminum engine block
  • LQ9 6.0L engine with flat top pistons raising compression to 10:1

Gen IV LS Engine Car Applications

  • 2005-2007 Corvette, 2005-2006 GTO, 2006-2007 Cadillac CTS-V: 6.0L LS2
  • 2008-2013 Corvette, 2009 Pontiac G8 GXP, 2010-2015 Camaro, 2014-2017 Chevrolet SS: 6.2L LS3
  • 2010-2015 Camaro with auto trans: 6.2L L99
  • 2006-2013 Corvette Z06, 2014-2015 Camaro Z28: 7.0L LS7
  • 2009-2013 Corvette ZR1: 6.2L LS9
  • 2009-2015 Cadillac CTS-V, 2012-2015 Camaro ZL1: 6.2L LSA

*Note, stay away from the LS4 found in FWD applications. The bellhousing bolt pattern is specific to FWD transaxles, and the compact front accessory drive is not easily adapted to RWD swaps either.

Gen IV LS Engine Truck Applications

The Gen IV engines share a vast majority of design elements with the Gen III engines and many of the internal parts can be interchanged.

  • Provisions for Active Fuel Management (AFM) and Variable Valve Timing (VVT) were added
  • Cam sensor relocated to the timing chain cover (Gen III cam sensor was located at the top/rear of the engine block)
  • Single bolt cam gear (Gen III were 3 bolt)
  • 58X reluctor wheel for crank sensor (Gen III was 24X)
  • Connecting rod design was changed to enhance strength
  • 6.0L and 6.2L truck engines used rectangle port heads (LS3 style heads)

You can find more detailed information in our Junkyard LS Swap Guides as well. Part 1 we cover Gen III LS engines, while in Part 2 we cover the Gen IV LS engines. Lots of good reading there, so be sure to visit those links for more details before you hit your favorite salvage yard!

Are LS Connecting Rods the Same?
A Gen III LS Connecting Rod

Except for the LS7’s unique titanium connecting rods, the Gen III and Gen IV rods do have some minor differences that, while interchangeable, make the Gen IV rod the preferred rod if using them in a budget build. Due to the fractured cap design of the stock rods they are not easily resized, and for serious power LS engine builders recommend going with aftermarket rods.

-Gen IV have a thicker I-beam design which handles more horsepower and is better suited for high horsepower turbo and supercharged applications

-Gen IV have an increased surface area at rod cap split which enhances stability of bearing bore roundness

-Gen III use a press fit wrist pin while Gen IV use a floating wrist pin; if upgrading a Gen III engine to Gen IV rods the pistons will also need to be Gen IV due to this floating wrist pin change

Are Cathedral Ports Better?

The LY6, L96, and L76 6.0L engines as well as L92, L9H and L94 6.2L engines all have rectangle port heads with the larger 257cc intake port volume. Rectangle port LS3 style heads can be found on some truck engines as well. For comparison the popular cathedral port “243” heads have a 210cc intake port volume. The larger intake port design works very well on the 6.0L and larger engines. Some racers looking for high rpm power out of a 5.3L engine have used these heads but for most street applications the smaller cathedral port head is better suited to the 5.3L engine size. The cathedral port maintains a higher velocity at the lower rpm range and will result in more low-end torque for the smaller displacement engines. One additional note on the rectangle port heads is that they use an offset intake rocker arm, making their rockers specific for the intake and exhaust, whereas the cathedral port heads use the same rockers on both intake and exhaust.

A Comparison of LS Engine Intake Port Shapes And Locations
Should You Do an AFM Delete?

Active Fuel Management (sometimes called Displacement on Demand) is a technology GM uses on some of its V6 and V8 engines to improve fuel economy to meet EPA requirements. This is accomplished by disabling some of the engine’s cylinders under low load situations. When swapping your LS engine into a muscle car and adding a performance camshaft this system will need to be deleted if your LS is equipped with it (a quick way to tell is inspect the engine valley cover; a smooth cover means no AFM/DOD and one with raised oil passage ridges has AFM/DOD). The cam and lifters will need to be changed to non-AFM components, which also means removing the cylinder heads to install new lifters (one of the few negatives of the LS family). Speedway Motors offer a 5.3L AFM delete kit as well as a 6.0L AFM delete kit to completely remove the system. These kits can be combined with a camshaft of your choice to eliminate the AFM system.

You’ve Found Your LS to Swap, What’s Next?
LS Engine Freshly Pulled From a GM Truck

Through our identification chart you’ve scored that deal of an LS at your local salvage yard and you’re ready to start yanking out your old Gen I small block. Slow down there, we know you’re excited to get started, but make sure you have everything you need to do the swap right without frustration by going through our LS Swap Guide here on the Toolbox.

Happy hunting, and be sure to start adding all of your LS swap parts needs to your LS swap wish list you can create right at the top of our home page (just look for the “My List” button). Then, when you find the right part for your build simply use the “Add to a list” button on the product page. It’s that simple to star creating your LS swap product list!

Updated by Mark Houlahan

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