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Let’s Talk Torque: LS Truck Upgrades

Words and Photos: Richard Holdener

We all know that adding a cam to an LS application is the go-to method of power production. The question then becomes, how much cam do I add? Cam swaps can easily improve the power output of an otherwise-stock LS application by over 100 hp, but are all LS owners looking for maximum power production? Let’s face it, not every LS motor is an 8,000-rpm, fire-breathing monster. Most, in fact, are used as daily transportation, or for hauling and/or towing. Sure, if you have a Camaro, Corvette or just swapped a turbo 5.3L into your Fox Ford, by all means go with a big stick. If, on the other hand, you happen to drive a ¾-ton Silverado, or other 6.0L-equipped car or truck, that just needs more get up and go, this test is for you. The needs of a daily driver differ greatly from a dedicated race car, or even a dual-purpose, street/strip machine. Things like low-speed torque, idle quality and converter compatibility all take precedence over maximum peak power.

Since getting big power numbers from an LS is so easy with wild cam timing, we had to purposely restrain ourselves when choosing a cam for this 6.0L test. As tempting as it was to go big, we chose our XR265HR grind from COMP Cams knowing full well that the 6.0L in question would spend the majority of its time below 5,000 rpm. We also knew that torque at 3,500 rpm was every bit as important as power at 6,000 rpm. What we wanted, was to improve both peak power AND peak torque production, but to do so without hurting low-speed torque. In fact, the ideal situation would be to improve torque through the entire rev range, something often difficult with a simple cam swap. Generally speaking, more aggressive cam timing often trades power at one end of the rpm range for the other. Big peak power gains come at the expense of low-speed torque, so a compromise is usually in order.

Looking for a cam that was oriented toward the daily driver, we selected an XR265HR grind (pt#54-424-11) from COMP Cams. The XR265HR cam offered a .558/.563 lift split, a 212/218-degree duration split and 115-degree lsa. The lift numbers allowed use of factory LS3 valve springs, but we opted to install a set of 26918 valve springs from COMP Cams. To further the gains offered by the cam upgrade, we decided to replace the factory 317 heads on the 6.0L test motor with 706 heads from a 5.3L. Before you get all up in arms about how the 317 heads flow like 243 heads and the small-valve 706 heads would be a step-down, let’s take a look at the facts. While it is true that the 317 heads flow slightly more than the 706 heads, the difference in flow is minimal, and those gains are primarily at higher valve lifts. Besides, the minor flow gains required a larger intake valve, and part of the reason the 706 heads make better power than the 317 heads is the smaller valve. Similar flow through a smaller valve equals improved efficiency.

Of course, no discussion on the topic of cylinder heads would be complete without mentioning the combustion chambers. The most obvious answer for the superiority of the 706 heads over the 317s is the smaller combustion chamber. The smaller chamber increases the static compression, which in turns improves power. Run back to back on a smaller (but 470-hp) 5.3L, the 706 heads were better by over 20 hp (and even more torque) over the better flowing 317s. According to industry experts, the 317 chambers are not just bigger, the design is less efficient, even when milled. Besides, the 706 heads can be had for almost nothing because everyone upgrades to something else. Given the fact that the 706 heads are cheap, readily available and offer big power gains over the 317 heads, we’d say they are the hot ticket for 6.0L guys looking to improve both power and fuel mileage. When teamed with a cam swap on our 6.0L, they allowed us to get both big power and torque gains without sacrificing any power down low.

To test our daily driver head and cam package, we selected a 6.0L test mule. Originally a rec-port (LS3)-headed LY6, we modified the 6.0L with the installation of an LQ4 cam, 317 heads and a standard (non-TBSS) truck intake. This LY6/LQ4 hybrid 6.0L (LY6 pistons being the only difference) would serve as our baseline for the upgrade. Run on the dyno with long-tube headers, a factory manual throttle body and FAST XFI management system, the 6.0L produced 401 hp at 5,200 rpm and 432 lb-ft of torque at 4,400 rpm. After the baseline, we replaced the stock LQ4 cam with the COMP XR265HR grind then swapped out the 317s for the 706 heads. This combination was run with the same truck intake and throttle body. After the modifications, the 6.0L produced 487 hp at 6,100 rpm and 478 lb-ft of torque at 4,800 rpm. The combination of the extra torque offered by the head swap, and power offered by the cam swap, allowed the modified 6.0L to produce more power through the entire rev range than the stock version, just the thing for a daily driver.

Graph: 6.0L LQ4/LY6 Hybrid-Stock vs 706/COMP 265 Upgrade

Our test motor was actually an LY6 6.0L equipped with an LQ4 cam, then topped with a set of 317 heads and truck intake. Run in this configuration, the hybrid 6.0L produced 401 hp and 432 lb-ft of torque. The torque production offered by a stock 6.0L was decent, but the power sure fell off quickly. While a cam swap can cure the horsepower deficiency, increasing the static compression with a set of 706 heads added fuel to the fire. The combination of stock 706 heads and a COMP XR265HR cam improved both peak power and torque, from 401 hp and 432 lb-ft to 487 hp and 478 lb-ft of torque. Even more importantly, the upgrade improved torque through the entire rev range, exactly what you want in a daily driver!