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.)

Almost as many camshaft options are available, as there are opinions as to which profile offers maximum performance. For this application, we're more interested in torque than horsepower, and that limits the field to cams with relatively short duration and tight lobe separation. As a means of minimizing idle quality degradation, the cams for LS and other late-model engines are commonly ground with 114 degrees of lobe separation. Since we were working with short duration specifications, idle quality wouldn't be much of an issue, so we tightened the LSA to 112 degrees. Combined with an intake duration of 208 degrees and exhaust duration of 214 degrees (at 0.050 inch lift) this cam would theoretically put a nice bump in the torque curve-especially considering its 0.554 inch intake and 0.559 inch exhaust lift.

Unfortunately, things in magazine land are about like they are in your garage or on the racetrack; they don't always turn out as planned. When we reintroduced the truck to the rollers at Atlanta Chassis Dyno, horsepower was up significantly, but torque increased only 5 lb-ft. (More details below.)

Our selection of cylinder heads wasn't quite as straightforward as our cam choice. According to Vmax Motorsport's Pete Incaudo, the most economical option for a towing engine-aside from leaving the original heads unmolested-is pocket porting and a multi-angle valve job. However, we had a pair of Vmax Motorsports CNC-ported LS1 cylinder heads on hand for another project that never materialized, so we figured "why not?" They had already been angle milled and their combustion chambers measured 60cc, the same as original equipment 5.3L heads.

Ironically, before the advent of LS6 cylinder heads, a popular option was to install 5.3L truck heads on 5.7L Camaro and Corvette LS1 engines as a low cost means of increasing compression ratio. (The ports in the truck heads are virtually identical to those in LS1 heads, requiring only the replacement of the 5.3 heads' 1.89 inch intake valve with an LS1 2.0 inch valve for equivalent airflow capacity.)

Used cylinder heads for 5.3L truck engines are readily available at reasonable cost, so if you don't want your truck apart for as long as it takes to get the head work done, you can buy a pair of used 5.3L heads and have them prepared and ready to install before removing the original heads (which you can subsequently sell). Irrespective of the castings you select, keep in mind that 5.3L engines have a 3.78 inch bore diameter, which limits maximum valve diameter. Valves larger than those used in stock LS1 heads (2.0 inch intake, 1.55 inch exhaust) will be unceremoniously introduced to the top of the block.

Valvesprings are another component of the camshaft/cylinder head equation that can lead to long, sad stories if ignored. Many aftermarket camshafts open the valves in excess of 0.500 inch which will put stock valvesprings into coil bind, as was the case with the cam we used. To accommodate cam lift, we installed Comp Cams 26918 beehive springs, which can be used with cams having up to 0.600 inch lift.

The final modification in our quest for increased performance was the installation of a Vmax Motorsports CNC-modified throttle body in place of the less glamorous original version. Even though throttle bore diameter is unchanged (it wouldn't make sense to enlarge it because that would make it larger than the opening in the intake manifold), the CNC modifications recontour and smooth the entry, and that delivers a significant airflow increase over the entire rpm range.

After installation of the cam, heads and throttle body was completed, we did some testdriving before returning to the dyno. One of our concerns was that the stock injectors didn't have a high enough flow capacity for the engine's higher air processing capability. A few wide-open throttle blasts, confirmed these suspicions, as injector pulse width above 5,000 rpm was excessive.

In addition to differing in flow rate, the injectors used in various LS engines also differ in overall length and connector style. Depending on the engine and year of manufacture, LS injectors can be the "long-style" with EV1 connectors, "short-style" with EV6 connectors, "short-style" with Delphi connectors or "extra-short-style" with EV6 connectors. Most 4.8- and 5.3L truck engines are equipped with "short-style" injectors that accept either Delphi or EV6 connectors. That being the case, injectors from an LS2 Corvette engine can be installed with no modifications-except for the connectors on trucks originally equipped with Delphi connectors. The LS2 injectors are a good choice because take-out sets are available at relatively low cost from companies like Cody Motorsports.

Now for the results of the second dyno test session-which didn't provide the data we anticipated. In retrospect, we really should have expected relatively little increase in midrange torque, considering that with the stock cam, (which has a paltry 190 degrees of duration at 0.050 inch lift) the engine's torque peak of 308 lb-ft was at 4,000 rpm (which is both the factory specification as well as the actual test results logged at Atlanta Chassis Dyno). That being the case, even with 112 degrees of lobe separation, a duration of less than 200 degrees will probably be required to substantially increase torque between 3,000 and 4,000 rpm.

On the horsepower side of the ledger, improvements were much more dramatic. The power curve jumped by 34, hitting a peak of 302 at 5,300 rpm. And although the engine's torque peak moved to 4,600 rpm, the reading at 4,000 rpm was identical to that recorded by the stock engine.

In spite of the torque readings recorded on the dyno, at part throttle, the truck seems noticeably more powerful, both in normal driving, and when towing. As might be expected, once rpm pushes past 4,000, the difference in performance is dramatic.

We have a few more modifications in mind to pump up midrange torque. Depending on how they work out, you may see "Tow Story 3" in a future issue.

SOURCE
Atlanta Chassis Dyno
1855 Buford Hwy.
Duluth
GA  30097
770-623-9789
www.atlantachassisdyno.com/
EFILive
Cody Motorsports
Lawrenceville
GA
VMax Motorsports
813-469-4665
www.vmaxmotorsports.com
COMP Cams
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