In the time-honored fashion of car crafters since the first days of hot rodding, gearheads have taken the latest engines and stuffed them into earlier, lighter, and more affordable cars all in the name of going fast. Your grandfather stuffed flathead V-8s in Model A roadsters, but for the latest generation of enthusiasts, it's the Gen III engines that are the new darlings of the GM engine swap set.
The Gen III began its production run with the new '97 C5 Corvette and was quickly followed in the Camaro and Firebird. These LS1 and later LS6 engines are all-alloy-light and make outstanding power based on excellent cylinder head architecture, and they feature a distributorless coil-near-plug ignition that, while electronically complex, also offers the potential to set the engine farther back in the chassis since you don't have to access a distributor! Less well known but just as important is the fact that all fullsize GM trucks built since 1999 also utilize the Gen III configuration in an interesting series of displacements that mirror its first-generation small-block heritage. The GM truck/SUV Powertrain lineup includes a range of engines displacing 4.8L, 5.3L, and 6.0L. The 4.8L and 5.3L engines displace 293 ci and 325 ci respectively, while the 6.0L pencils out to 364 ci. If you think of the 4.8 as a large 283 and the 5.3 as a small-bore 327, and the 6.0L as a mild stroker 350ci, then you're right on target.
The original Gen III engine made its GM splash in the '97 Corvette followed quickly with Camaros and trucks. Note how this Corvette front accessory drive kicks the alternator outboard of the engine with the A/C compressor located on the lower passenger side.
bSimilarities
All these Gen III engines are based on the same 4.400-inch bore centers and deck heights along with main, rod, and cam bearing journals. All the heads interchange, as do cams, valvetrain, intakes, oil pans, valve covers, and accessory drives. This makes mixing and matching parts from boneyard engines easy, but care needs to be taken to match the pieces properly. The truck engines all utilize iron blocks with aluminum heads--only the '99 LQ4 6.0L engine came with iron heads. The only exception to this is the current '04 SSR truck 5.3L engine that employs an aluminum block and heads to trim a little fat in the portly pickup.
This similarity between the engines makes especially the truck powerplants attractive for engine swappers. The hot ticket if you're looking for a bigger-inch engine would be the LQ4 and LQ9 truck, Cadillac Escalade, and EXT engines. These 364ci engines would be perfect fodder for an early Camaro/Chevelle engine swap if you don't mind the extra weight of the iron block. The advantage is that these engines will probably be less expensive than the all-alloy Corvette or Camaro/Firebird LS1/LS6 engines. The weight difference is roughly 100 pounds.
While this '03 4.8 truck engine may not look as sexy as a Corvette LS6, it is nonetheless a Gen III engine. All the truck engines use iron blocks, but otherwise can use all the same high-performance parts like heads, cams, and intakes. Note this truck accessory drive mounts the alternator up high on the driver side with the power steering pump tucked underneath. The A/C compressor is mounted low on the passenger side.
Differences
While the basic engines are the same, each application varies wildly in terms of intake manifolds, water pumps, front accessory drives, and oil pans. The Corvette engines have the best and shallowest oil pan for pulling lateral g's, but it's also the most difficult to fit into an earlier musclecar. The F-car rear-sump pan is 51/4 inches deep and offers the most potential, but even it will usually require surgery. We've run across a total of five different oil pans with two variations on rear-sump truck pans with the C/K truck pans measuring 81/2 inches deep.
There are at least three distinctly different accessory drives, and the photos illustrate the basic differences between the Corvette, F-car, and truck systems. The water pump also changes between the cars and trucks, and there are several variations on the exhaust manifolds between the Corvette, Camaro, and trucks. The accessory drives not only vary by positions of the pumps and alternators but also by the depth of these systems. The Corvette tucks the drive pulleys closest to the front of the engine, with F-car next, and the trucks placing them the farthest forward of the three. Keep this in mind if you're considering mixing and matching pieces within these accessory drives. That could be a nightmare.