In "Tow Story 1," we covered a variety of basic bolt-on modifications designed to enhance the towing capability of trucks equipped with GM's 5.3L LS engine. Those mods-high-flow catalytic converters, low-restriction muffler, electric-fan conversion and PCM reprogramming-made a noticeable improvement in throttle response and power throughout the engine's rpm range. On Atlanta Chassis Dyno's Dyno-Jet, the truck cranked out an impressive 268 hp and 308 lb-ft of torque, which is an increase of 24 hp and 15 lb-ft of torque compared to a stock engine.

With those mods completed, and the truck running better than it ever had before, it was time to get serious. So, we threw caution to the wind, and without adult supervision, installed a performance camshaft, ported cylinder heads and a modified throttle body. These modifications obviously made a dramatic difference in the engine's personality, so after finishing the wrench work, we again fired up EFILive's FlashScan software and reprogrammed the PCM.

If you've never swapped a cam in an LS-series engine, (also called a Gen3 and Gen4 small-block) you're in for an eye-opening experience. You can remove the cam without removing the lifters, which is a good thing because you can't remove the lifters unless you first remove the cylinder heads. Unlike traditional GM small- and big-blocks, with lifters accessible when the intake manifold is removed, the lifters in LS-series engines are housed in separate chambers which lie between the central valley and the cylinder walls. Those chambers are covered by the cylinder heads.

Another unique aspect of LS engine architecture is the method of lifter retention. They're kept in place by plastic trays, and when the pushrods are removed, and you rotate the cam, the lifters are held in the raised position by the trays. If you plan to do a cam swap and not remove the heads, all you have to do is spin the cam a few revolutions and pull it out of the block. As insurance against having a lifter fall out of a tray and into the pan, it's advisable to use pencil magnets (inserted through the pushrod holes), but countless cam swaps have been completed with nothing more than the trays doing the holding.

The unfortunate part of this arrangement is that the plastic trays are the only components that prevent the lifters from rotating in their bores. Although they are obviously manufactured of super high-strength material that's designed to survive in a hot and hostile environment, the trays are not immune to cracking. And a crack in the wrong location can allow a lifter to rotate, ruining it and the lobe on which it's riding. Consequently, when installing a performance-type camshaft, it's advisable to remove the cylinder heads and replace the trays if an engine has more than 50,000 miles.

Another surprise for anyone who has never had an LS engine apart is the timing chain, which is a single row roller-type. Aftermarket double row chains are available, but certainly not a requirement for anything less than a highly modified street performance or race engine. A more worthwhile upgrade is Comp Cams' timing set with adjustable cam sprocket. As with those designed for traditional small-blocks, many adjustable timing chain/sprocket sets incorporate multiple keyways in the crank sprocket as the means of advancing or retarding camshaft position. The Comp set features an eccentric bushing in the cam sprocket that can be rotated with an Allen wrench. Marks scribed on the sprocket indicate the degree of advance or retard. (Comp Cams also offers lower-cost timing sets without the eccentric bushing.)