Hopping GM's 6.0L LS-Series Small-Block
Pick up 74 hp and 53 lb-ft on a 6.0L truck engine with basic bolt-ons and a computer tune-up.
General Motors' LS-series small-block engines have been in production for over a decade, but it's only been within the last few years that they have really hit critical mass among average hot rodders, who are now finding them to respond superlatively to traditional hot rod power adders. One engine builder that's jumped on the LS bandwagon is Duttweiler Performance, renowned for its hard-running, high-tech, EFI turbo Buick V-6 and classic Chevy V-8 engines. When HOT ROD decided to evaluate the current state of bolt-on LS hop-ups, Duttweiler was our first choice. Its sophisticated Froude F24 dyno controlled by state-of-the-art Digalog Benchmark software enables true wideband pulls, so the facility provided the perfect opportunity for evaluating a late-model engine under simulated street-driving conditions—and proprietor Ken Duttweiler is totally at home with modern PC laptop tuning software.
All we needed was a representative motor. The all-aluminum Gen III LS1 and LS6 engines displace 5.7 liters (346 ci). Unfortunately, their cast-in-place engine liners make overboring difficult. Although their improved liner design makes them a more viable rebuild candidate, the late LS2 6.0L (364ci) all-aluminum cores are still relatively rare. That left the most bang for the buck: a 6.0L truck engine. Not only are the truck engines much more plentiful than the LS1/LS6 engines that are found only in selected high-perf rear-wheel-drive cars, but in the past most have been based on easily rebuildable iron blocks (max overbore 0.030 inch). Besides, a stock-bore 6.0 nets you 19ci over the 5.7L car engines.
The best of the iron-block, aluminum-headed 6.0L truck engines was RPO LQ9, which General Motors Performance Parts (GMPP) also sold as a complete crate assembly that included just about everything from throttle body to flexplate. GM shipped us one for test-mule service. PN 19156262 was rated at 345 hp and 380 lb-ft (SAE net) with 10.08:1 advertised compression and heads similar to the vaunted Corvette LS6, except for larger combustion chambers (making them more suitable for a blower, if you're going that route).
Although this crate engine has recently been discontinued, some local dealers may still have a few. Mr. Goodwrench service replacement long-blocks are also still available, and there are also lots of cores in the wrecking yard: The 345-hp, 6.0L LQ9 was installed in selected '02-'06 Cadillac SUVs and '04-and-later Chevy Silverado SS pickups. Look for a 6.0L block with the No. 317, LS6-like head castings. Some 325-hp, 6.0L LQ4s also got these heads. Allegedly, the main difference between the two engines is the LQ4's half-point-lower 9.41:1 compression ratio.
The crate engine was installed on Duttweiler's dyno set up the way it would be in a production truck, less the factory airbox but with the factory exhaust system and accessories. Running off the stock computer using the truck fuel and spark calibration, the engine produced 355 hp and 396 lb-ft of torque, as measured with the standard temperature and pressure-correction factor. GM claims 345 hp and 380 lb-ft, as rated by the more conservative "net" correction factor.
Headers and Exhaust
Time for some breathing exercises—a set of equal-length Dynatech stainless steel '04-'05 GTO headers, 211/42-inch dual pipes (without cats), and dual, free-flowing Flowmaster Super 40 mufflers. While still running the stock long-runner truck intake manifold and stock fuel and spark calibration, freeing up the exhaust made the engine come alive and netted 24 hp and 25 lb-ft at the peaks. The engine was now churning out 379 hp and 421.7 lb-ft, with the overall powerband broadened over the baseline. From 1,600 to 5,700 rpm, average power and torque were up across the board by 15.8 hp and 21.5 lb-ft.
Dynatech's '04-'05 GTO stainless steel headers were tested both with and without Dynatech's complementary high-flow catalytic converters. The big 13/4-inch primaries and 3-inch collectors turned out to be the best single bolt-on power improvement in this test series.
The factory computer controls many more functions and is ultimately much more versatile and sophisticated than all but the highest-end aftermarket systems. Components are widely available in wrecking yards, but the problem has always been the factory hardware's non-user-friendliness. Average end-users couldn't reprogram them, and late models have sophisticated vehicle antitheft system (VATS) provisions built into the computer. But now programs exist for completely hacking every function of the factory computer—including VATS removal. They run on a normal Windows-based PC and look and operate just like any other Windows XP-compatible program. Duttweiler likes HP Tuners' VCM Suite. One $500 standard license for this software gives the end-user the right to tune at least two (and in some cases, four or more) vehicles; additional credits can be purchased to tune additional cars.
Five hundred bucks seems like a lot of money, but in the LQ9's case it was money well spent. Fuel and spark table analysis showed that the headers so increased the mass flow through the engine that the computer was now trying to read an area of the spark table that under the factory calibration was extremely conservative and was removing excessive amounts of timing lead from the engine. As is typical of wide-open-throttle factory calibration, the air-fuel ratio was also rich. Tuning up the spark and fuel netted 29 hp and 19 lb-ft, increasing peak output to 408 hp and 440 lb-ft. Dialing in the spark and fuel curves nearly doubled the headers' power and torque gains.
Everyone knows catalytic converters suck for performance—no true hot rodder wants to plug up the engine. Back in the days of crude, first-generation pellet-style converters, there was some validity to this belief. But engineers have had 30 years to refine converter technology, and as technology goes, 30 years is a lifetime. Dynatech makes some high-tech catalytic converters designed to be used with its headers. Installing dual miniconverters after the headers but still running through 211/42-inch dual pipes into the dual Flowmaster 40 mufflers cost only 0.3 hp and 7.1 lb-ft at the peak, and just 2.6 hp and 3.8 lb-ft on average between 1,600 and 5,700 rpm. Overall, the engine ran so well with the cats that they were left in place for all subsequent mods.
A commonly held belief is that a short-runner, car-style intake manifold should outperform a poky long-runner truck intake. On a truck engine, switching to a car-style, short-runner intake is not a straight bolt-on. You must install a passenger-car front accessory dress to clear the lower-mounted throttle body. Fortunately, Duttweiler had a complete Camaro drive setup handy.
With the accessory drives switched over, Duttweiler tested the original stepped-floor LS1 intake (stock on '97-'01 Corvettes and '98-'01 F-cars), the flat-floor LS6 manifold (also used on most LS1 builds from late '01 and up), and the Generation IV LS2 intake. Compared to the LQ9 truck long-runner design, the LS1 intake lost 9 hp and 11 lb-ft. The LS6 intake was a hair better but certainly not enough to justify the complexity of the changeover unless you had a hood-clearance issue. As for the LS2 configuration—fuhgedaboudit! Despite a larger 90mm throttle body, when compared to the best headers/cats/truck intake configuration the LS2 manifold was down nearly 8 hp and 7 lb-ft at the peak and 6.7 hp and 9 lb-ft on average.
FAST's short-runner, car-style LSX intake is a popular bolt-on. And for good reason: In our tests, equipped with the 90mm throttle body, it raised the power and torque peak outputs to 419.8 hp and 440 lb-ft, respectively, a gain of 11.5 hp and 6.9 lb-ft over the truck intake's headers-with-cats configuration. Although this hot rod manifold was down (just slightly) on torque below 2,800 rpm as well as in under-3,200-rpm horsepower production, it more than made up for it in the midrange and top end, to the tune of raising average 1,600- to 5,700-rpm output about 6 hp and 10 lb-ft. Power output above its 5,400-rpm power peak also fell off less precipitously. This manifold should be worth even more when coupled with a high-performance camshaft.
High-Ratio Rocker Arms
Stock LS-series engines already have roller-fulcrum 1.7:1-ratio rocker arms (with roller fulcrums but not roller tips). Although a step up from the old-school small-block's 1.5:1 stamped rockers, unlike those legacy V-8s (except for the LT4), LS-series engines have a non-adjustable net-lash valvetrain. More radical cams require a means of adjusting the valvetrain, but even if you don't want to tear apart the engine to install a new cam, moving up to higher-ratio rocker arms is potentially worth some power—and it's a quick and simple bolt-on with Crane's adjustable 1.8:1 full roller rocker arm kit. Stiffer pushrods are also included in the Crane kit, as experience has shown that the stock soft pushrods are one of the LS-series engine's weak links for performance usage
Moving up from 1.7:1 to 1.8:1 is worth some more valve lift—in the LQ9's case, about a 0.027-inch increase to 0.494/0.507. But according to Crane, the average overall improvement is more than the raw numbers indicate because the rockers incorporate quick-lift technology. By positioning the pushrod cup lower in the rocker than stock, Crane effectively increases the rocker ratio during the early and late lift cycle as the rocker arm moves through its prescribed arc. As tested here, the Crane rockers helped the engine produce the highest numbers seen in this initial test series: 429 hp and 449 lb-ft.
Oil and Oil Pans
Up to this point all the tests had been conducted using the stock GM deep-sump truck oil pan and the 5W-30 factory oil (yes, GM delivers the crate engine with oil). It is felt in the enthusiast community that the truck pan is a rather crude design; its deep sump often presents ground clearance issues when installed in a low-to-the-ground classic hot rod. Could another pan do better? Duttweiler had two he wanted to try—a factory LS2 Corvette pan and a new Moroso retrofit design—but to maintain consistency during the cam swaps, the 5W-30 GM factory oil was replaced by some of Duttweiler's normal in-shop Lucas 10W-30 oil supply and the engine rebaselined, still with the 6-quart truck oil pan and standard truck windage tray. With the slightly heavier oil, the engine was down a tad: 2.2 hp and 4.1 lb-ft at the peaks, 2.9 hp and 4.7 lb-ft on average.
Reputedly, the '05 and later LS2 Corvette oil pan with its sophisticated internal baffling is better for a handling application than the truck pan; its shallow sump is also more adaptable to older rear-steer chassis. (Do not confuse this pan with the '04 and earlier LS1/LS6 Corvette pan that had side kick-out wings and doesn't fit anything besides a Corvette.) The Moroso pan is specifically designed to clear most classic muscle car chassis, with the exception of early '62-'67 Chevy IIs. In actual testing, neither of these pans proved superior to the truck pan on a stationary engine dyno. However, these tests retained the stock truck full-length windage tray; results may differ with a tray optimized for the other pans.
As the engine now stands, the highest recorded numbers were with the Dynatech headers, high-flow cats, recalibrated computer, stock truck oil pan, 5W-30 oil, and Crane 1.8:1 rockers. Compared to the initial stock baseline configuration, Duttweiler had gained nearly 74 hp and 53 lb-ft with bolt-ons and tuning. In the ultimate configuration so far, the engine was making almost 430 hp and 450 lb-ft at the peaks. It churned out over 400 hp from 4,700 rpm on up, with over 400 lb-ft of torque from 2,900 to 5,600 rpm. Of all the changes, adding the headers and tuning the computer garnered the most improvement, although the FAST intake and 1.8:1 rockers should really come into their own when coupled with big cams and higher-flowing heads. Big cams? High-flow heads? Come back next month. We're just getting started.