GM's V8 LS engine onslaught is now well into 15 years in the making. Along the way, it has evolved much more quickly than its Geritol-eligible cousin, the Gen I small-block Chevy. This LS evolution has brought with it a certain amount of confusion, and we thought it would be a good idea to document how the engine has been revised over the last few years. Car crafters are inveterate tinkerers, which means we can't leave anything alone. A strong, robust 5.3L could probably benefit from a better cam or better heads and a different intake. But at the same time, you have to be careful with what will interchange and what will not. We will be dealing mainly with the most popular of the LS engines, including the LS1, LS2, LS3, and all the affordable iron-block truck engines. While we won't ignore those esoteric engines, such as the dry-sumped LS7 and the wonderful (and expensive) supercharged LS9 and LSA powerplants, we won't spend much time with them either. This also goes for the variable–cam timing and AFM (active fuel management) engines. The goal here is to get into the interchangeability and differences of the most common LS engines. This information will ultimately make it easier for car crafters to bolt these new powerplants into the older machines we love so much.
The Displacement Curve
The LS has come in a bunch of different displacements that allow some fun projects that include boring and stroking, but it's always good to have a reference point from which to start. Let's look at the bore-and-stroke combinations that create the stock displacements. We also threw in a few aftermarket displacement combinations, just for fun.
Gen III Versus Gen IV
With LS engines topping the engine-swaps hit parade, it's important to know what you are buying. The Gen III engines appeared between 1997 and 2005, at which time GM updated the family to Gen IV status based on a few subtle yet significant changes. If you are considering purchasing a used LS engine, it's worth taking the time to learn how to spot a Gen III versus a Gen IV. The most significant change to the Gen IV engine is an internal change to the crankshaft position wheel, which went from a 24x (26 minus 2) to a 58x (60 minus 2) tooth count. The crank sensors also changed at this time and can be identified by color: 24x is black, while the 58x is gray. Perhaps the easiest way to spot a Gen IV engine is by the location of the cam sensor. In early engines, the cam sensor was placed at the back of the engine near the oil-pressure sending unit, while the Gen IV sensor was moved to the driver side of the front timing cover. Another easy way to tell if a stock engine is a Gen IV is by the fuel lines. Gen III engines used a return line, while most Gen IV engines converted to returnless fuel systems (the return line was eliminated). Electronic throttle control (ETC) really isn't a good way to differentiate these engines, as the Corvette was using ETC from the early years.
Displacement Switcheroo
The single most popular version of the GM LS engine is the iron-block 5.3L engine. As this engine was built in a dizzying variety of RPO versions, we have yet to find a quick way to differentiate the smaller 4.8L truck engine from its larger 5.3L sibling once the engine is removed from its parent vehicle. Both truck engines feature a 4.8L/5.3L casting mark in the front of the block that distinguishes them from their larger 6.0L cousins. However, the only way we've found to determine if an engine is actually a 5.3L version is to remove one cylinder head and measure the stroke. As you can see from our included bore-and-stroke chart (top of page), both the 4.8 and 5.3 use the same 3.78-inch bore, with the smaller engine featuring a shorter stroke. If the motor measures a 3.62-inch stroke, you have a 5.3L engine. If the stroke comes up shorter at 3.26 inches, the motor is a lowly 4.8L.
It's also important to note that GM built some aluminum-block 5.3L engines that if reconfigured with an F-car intake and accessory drive could be mistaken for an LS1 or even an LS6. Keep this in mind when shopping for used LS engines. It's a jungle out there.
Iron Versus Aluminum Blocks
We ran across this interesting factoid when attempting to bolt an F-car accessory drive to the front of an iron-block 5.3L: Though we're not sure if this is true across all aluminum-block LS engines, all the engines that we've seen feature three accessory-drive mounting holes on the front-left (driver) side of the block. We quickly discovered that the iron-block engines only feature one of the three holes drilled and tapped on the aluminum blocks. There is one boss that is present on the iron block that could be drilled and tapped, but the middle bolthole is completely missing because the material was removed in the iron block. This is not a deal breaker, but you at least need to be aware of this before spending money on an accessory drive that you may not be able to use.
Block Parts
The classic Car Craft approach to engine building is assembling parts from various obscure sources. Often this means working with a bare cylinder block. Like its Gen I ancestor, the LS has its own set of unique oil-gallery and water-jacket plugs, head pins, and various other pieces. The following chart lists some of the more obscure pieces, their GM part numbers, and their cost. You don't have to get these from Scoggin-Dickey, but the company offers an engine-block kit that includes the oil-galley plugs, water-jacket plugs, the transmission-alignment dowels, and that odd, plastic dumbbell oil-gallery bypass that is essential to the lubrication system. Chevrolet Performance (previously GMPP) lists a complete block kit part number in its catalog, but it is currently unavailable. Perhaps it will soon come back online.
Head Gasket
The LS series of engines use a multilayer steel (MLS) head gasket. We've noticed that Fel-Pro head gaskets are marked as left and right. Fel-Pro's Greg West says the company uses a welded stopper in between the multiple layers, and it works best when located in a certain position. West says you can use a "left" on the "right" by flipping them over (or vice versa) but that the gasket does not work as well that way. West also says that MLS gaskets generally don't work as well when they are thinner than 0.041 inch. We found some Cometic LS head gaskets with overall thicknesses down to 0.030 inch, which can be used to adjust compression. Keep in mind that a piston with a zero-deck height (flush with the block deck) needs a minimum of 0.040 inch for piston-to-head clearance.
Simple as One or Three
As is the case with its small-block Chevy antecedent, LS engine parts are wonderfully interchangeable. But there are limits. For example, beginning in 1997, GM used three bolts to retain the cam gear to the cam. Then in 2005, GM began the great Displacement on Demand (DoD) exercise—which later changed to Active Fuel Management because it sounded better—that employed a single bolt. Some LS engines continue to use the three-bolt camshaft and drive, so there are no hard and fast rules—or if there are, they are way too complex to outline here. Just be aware that not all LS engines use three bolts to adhere the camshaft.
Of Cathedrals and Rectangle Ports
Another big watershed event in the continuing LS engine legacy was the transition from the original cathedral ports to higher-flowing rectangle ports. Many believe this move was made strictly for performance, since many truck engines use a port opening that's similar to the Corvette LS3. The story we have heard is that the large port was created in conjunction with electronic throttle control in an effort to drastically reduce manifold vacuum at cruise speeds. This approach comes as a result of the sound engineering principle contending that it requires a certain amount of power to create high-manifold vacuum levels, which is negative work that reduces fuel mileage. The electronic throttle combined with the overly large rectangle-shaped intake ports contribute to reducing this negative work. One big benefit is that that these big ports flow equally big 300-plus cfm numbers right out of the truck-parts bin.
This port-volume explosion has sparked a major controversy in the LS community that is similar to the mosh pit over the big-block oval ports versus rectangle ports back in the '90s. There are supporters on both sides of this controversy, and we won't get into it here. Instead, let's deal with the basic differences. The most important piece of technical info to remember is that the rectangle port heads will not bolt on to just any LS engine. The rectangle port heads use large valves, which will not fit inside a bore diameter of less than 4.00 inches. This means that the rectangular-port heads won't work on a 4.8, 5.3, or even a 5.7L because the large valves will hit the edge of the undersized bore.
There is also the issue of combustion-chamber volume. The smaller displacement engines such as the 4.8L and 5.3L generally use a small, 61cc combustion-chamber volume to maintain a decent compression ratio, while larger 6.0L engines use a larger volume chamber of around 70 cc.
Crank Calls
If you are building an LS stroker with an aftermarket crankshaft, remember that these cranks use SAE 7⁄16-inch fine-threaded fasteners rather than the metric M11x1.5 bolts. For the LS stroker 404ci engine we built for our automatic-equipped Orange Peel Chevelle, we used SAE small-block 7⁄16-inch flexplate bolts.
Hydraulic Roller Lifters
Did you know that the hydraulic roller lifter in the small-block Chevy and the LS is almost the same? In fact, according to our pals at Crane Cams, the '97 to '00 LS engines used the same lifter as that on the small-block Chevy (SBC). Beginning in 2000, the lifter design changed very subtly. If you look at the photos, the recessed band in the middle is slightly narrower than the early LS and SBC. In addition, the oil-feed hole in the top band area is 90 degrees to the roller axle, while the early lifters place the oil-feed hole parallel with the axle. Crane tells us that if you were to use a set of SBC/early LS lifters in a '00-or-later LS motor, it's possible that the center relief band can drop out of the bottom of the lifter bore, which can bleed off oil pressure and possibly even move enough to lock up in the lifter bore, causing serious damage.
Oil-Pump Alignment Trick
The LS family of engines drives the oil pump directly off the crankshaft. The oil-pump gear case must be properly aligned over the crank before the oil-pump bolts are torqued. The procedure is to use a pair of 0.0015-inch feeler gauges between the pump gears and the case, as shown in the photo with the pump-case bolts finger tight. Once the clearance is set, you can torque the oil pump in place. Ken Duttweiler showed us a quicker way to do this by slightly tightening the oil-pump bolts and then turning the engine over several revolutions with a wrench. That will set the position of the gears in the pump case and allow you fully torque the oil-pump case bolts. We tried this, and the gears were perfectly aligned.
Front Timing Cover Alignment
A question that often comes up with the LS engines is how to properly position the timing cover after a cam swap. GM recommends an expensive cover-alignment tool, but following a recommendation from engine-builder Kenny Duttweiler, we made a slip-on hub from a used 5.3L truck balancer. We cut the inner portion of hub from the balancer, and then used a high-speed die grinder and an abrasive flapper to open up the hub's ID to allow it to slip over the crank snout. With the front cover installed, we cinched all the cover bolts and slipped the hub over the crank. We then tightened all the bolts, including the two that go in from the oil pan. The front cover seal should be properly aligned to the crank.
Swapping Valvesprings
Changing valvesprings has never been easier. Several companies, including Comp, Crane, and TFS, now have a trick tool that will compress the valvesprings on two valves for one cylinder simultaneously by just tightening one nut. If you are changing springs with the heads on the engine, all you have to do is remove the valve covers, rocker arms, and pushrods from the particular cylinder you are working on. Next, remove the spark plug and screw in an adapter that will allow you to pump compressed air into the cylinder. With the air in the cylinder holding the valves closed, install the tool and compress the springs. Remove the keepers, and then loosen the nut to release the springs. Then reverse the procedure to install the retainers and keepers.
Budget Thermostat
If you've ever worked on an LS engine, then you are probably familiar with the combination thermostat and housing that comes on most engines for both trucks and cars. If you've ever had to replace one, then you also know they cost between $30 and $40. But sometime around 2005, perhaps with the introduction of the LS2, GM separated the thermostat from the housing, and prices dropped dramatically. It took us a while to find the housing on Rock Auto because it is listed as a water-pump housing, but you can get a separate housing from AC Delco (PN 1510595) for $4.23 and a Gates 186-degree thermostat (PN 33963) for $5.75.
Connecting Rods
Among the multiple changes that accompanied the Gen IV LS2 in 2005, GM also moved to floating-pin pistons instead of the pressed wristpins in traditional Gen III LS engines. That means the connecting rods are not interchangeable between generations, unless the pistons and rods are matched. Rod length did not change, but there are bob-weight considerations that will probably demand custom balancing should you consider using a matched set of floating pin pistons and rods in a Gen III engine.
Budget LS Oil-Pressure Tap
One of the first things an engine-swapper might want to do is hook up a mechanical oil-pressure gauge to make sure his engine has sufficient oil pressure. The problem is that all LS engines are entirely metric. While metric adapters are available to replace the factory electric oil-pressure sending unit, there's a quick and cheap alternate route if you're willing to do a little work. The factory engines use a small aluminum cover above the oil-filter mount. You can merely drill and tap this cover for a mechanical or electric gauge connection.
