The Big Bang 6.0L Gen 4: Big Boost
hBy now, every LS owner should be familiar with at least one of the Big Bang LS engines. To refresh your memory, we kicked off the Big Bang testing at HOT ROD in 2011, when we took a stock LR4 4.8L short-block (that we originally thought was a 5.3L) and treated it to surfacing and a light ball hone, and increased the ring gap on the original stock rings. Then we added ported heads, a cam upgrade, and a new intake manifold. After pumping boost through the combination with a pair of turbos, we eventually produced more than 1,200 hp, and the thing was still alive!
We repeated this procedure with a larger 5.3L for Truckin magazine, then again with a 6.0L for Super Chevy. The 5.3L topped the 1,300hp mark, while the larger 6.0L thumped out 1,482 hp at 28.5 psi of boost. The one thing this trio of LS engines had in common was they were all early Gen 3 versions. When
GM introduced the Gen 4, the upgraded version included a revised block and stronger (full-floating) connecting rods. Since the rods were the eventual weak link in the LS, we decided it was high time to apply the Big Bang treatment to a Gen 4 engine.
The idea behind the Big Bang testing was pretty simple: We wanted to illustrate how much power the stock internals could withstand. Understand that just because the engine will throw down a huge power number for one dyno pull doesn’t mean it will do that all day—or even twice, for that matter. As you increase the power output, you decrease the life cycle of the components. Running at 350 hp, the engine will probably last 250,000 miles or longer. Run at 1,482 hp, the rods in the Gen 3 6.0L only lasted one run. The stock components were designed for the intended combination of power output and longevity. Racers have run these stock, bottom-end LS engines near the 1,000-flywheel-horsepower level for many passes. As you increase power, the number of potential (successful) runs decreases, and who wants to oil down a track or drive over their own crank at 150 mph? The point is, the big number does not mean you can go out and run it like that. These Big Bang engine tests were just exercises we did to find the breaking point, which we failed at (but more on that later).
For years, many LS enthusiasts scoffed at the 6.0L due to its larger bore. Their concerns included reduced head-gasket sealing and thinner cylinder-wall thickness, at least compared with the smaller 5.3L. Testing on the previous Gen 3 6.0L sure seemed to indicate that neither of these were a problem, as the connecting rod let go well before we experienced any issues with gasket sealing or wall integrity. Of course, the 6.0L is more expensive and harder to find than the
5.3L, so we suspect those are the major reasons for the continued popularity of the smaller engine. If you can get to the desired power goal with a 5.3, why go to the expense of the big-bore version, right? This is especially true of combinations looking for anything less than maximum power. Properly tuned, a turbocharged 5.3 LM7 (or other variant) can exceed 1,000 hp for race applications, or it can be used to tow a trailer at lower boost levels—such is the flexibility of a turbo engine. A 6.0, however, will make more power at any given boost level and improve spool-up, something important when running a larger turbo(s).
The Gen 4 6.0L chosen for this test was a 2008 LY6. This particular version had a number of desirable features, including rectangle-port 823 (LS3style) heads, a free-flowing intake, and variable valve timing (VVT). Secured online from LKQ, the high-mileage LY6 was well-worn and used for numerous
comparison tests before being drafted into Big Bang duty. Prior to running, the LY6 short-block was disassembled and treated to surfacing, a quickie ball hone, and a fresh coat of paint. The real reason for the disassembly was to increase the factory ring gap on the original piston rings. In most cases, piston failure under pressure is caused by insufficient ring gap. The rings heat up and the ends butt together and seize momentarily in the bore. The result is a broken ring land on the piston, but the culprit is actually insufficient ring gap. For our LY6, the ring gap was increased from a measured 0.019/0.024 inch to a little more than 0.030 inch for both top and bottom rings. The original rod bolts were also retained, as were the production lifters, but we swapped out the VVT timing setup for a 4X cam gear and a used chain.
Though we retained the stock rotating assembly, we made changes to the cam and top end. To ensure plenty of power, we secured a Lil John’s Motorsport Solutions Stage 3 twin-turbo cam from Brian Tooley Racing. This cam was a significant step up the performance ladder compared with the stock LY6 cam and offered 231/243 degrees of duration at 0.050-inch tappet lift, 0.605/0.614-inch valve lift, and 115+5-degree lobe-separation angle.
The cam was teamed with a set of CNCported Trick Flow Specialties Gen X 225 heads. Why replace the factory rec-port LS3 heads with cathedral-ports, you ask? Tested on the normally aspirated 6.0L, these Gen X 225 heads were worth 30 hp more than the stock rec-port heads. More power naturally aspirated (NA) equals more power under boost!
The heads were secured using GM LS9 head gaskets and ARP 625 head studs. Topping it off was a Holley Race Sniper intake. Designed for boosted applications, the heavy-duty intake is capable of withstanding more boost than the stock bottom-end ever could, with racers reportedly running as much as 40 psi. The shortrunner Race Sniper was also chosen to help reduce midrange torque production, something that really takes a toll on the cast internals. The Race Sniper was teamed with a matching 92mm Sniper throttle-body and 120-pound Holley injectors fed by an Aeromotive pump, which was further augmented by a 17-volt Kenne Bell Boost-aPump. Dialing in the all-important air/fuel and timing curves was a Holley HP ECU with a 3-bar MAP sensor.
With our engine at the ready, we installed it on the dyno at Westech Performance Group to establish a baseline in NA trim. The 6.0L did not disappoint us, generating peak numbers of 548 hp at 7,000 rpm and 462 lb-ft of torque at 5,500 rpm. Satisfied with our starting point, it was time for boost.
For this test, we duplicated the twin-turbo system run on the previous Gen 3 6.0L. The stainless turbo headers from DNA Motoring fed exhaust to a pair of S475 BorgWarner turbochargers supplied by LJMS. Originally equipped with larger T6 exhaust housings, we replaced them with smaller T4s for this application. Each S475 featured a cast impeller wheel, an 83mm turbine, and a 1.0 A/R. The turbos were chosen not only because they were ideally sized for maxi-
mum spool-up on our 6.0L but because they could support 1,000 hp each—more than enough for our stock bottom-end test. Controlling the boost was a pair of Hypergate45 wastegates from TurboSmart. We also combined different springs and a manual wastegate controller to reach our eventual ceiling of 29.2 psi. Cooling the heated charge temp was a dual-core, air-to-water intercooler from CXRacing. Run with ice water, the core dropped inlet air temps by a good 200 degrees.
After running the Gen 4 6.0L in NA trim, we applied boost gradually, allowing us to dial in the tune. Since boost is the great multiplier, it doesn’t take much for a 548hp engine to start making some serious power. Run at 14.4 psi, the twin-turbo 6.0L produced 1,078 hp, while 16.0 psi upped the ante to 1,150 hp. Cranking up the boost knob to 17.5 psi allowed us to eclipse the 1,200hp mark, with a peak of 1,213 hp, but big things started to happen beyond 20 psi. Running 22 psi, the 6.0L produced 1,349 hp, but 26.6 psi put us at 1,433 hp. We were just below the power output of the previous Gen 3 6.0L, which broke at 1,482 hp. This is when we started to worry whether this Gen 4 engine had enough in reserve to eclipse the Gen 3. Another tickle on the old power knob brought the boost to 29.2 psi, where the 3-bar MAP sensor called it quits. We are happy to report that the MAP sensor gave up the ghost at the top of the rev range and allowed us to make a full pull to the tune of 1,543 hp and 1,256 lb-ft of torque. Imagine that: an engine originally designed by GM to produce approximately 400 hp was now making close to four times that amount.
It is safe to say the Gen 4 rods are stronger than the Gen 3 versions, and that these dang LS engines never cease to amaze us.
01] This Big Bang adventure started with a 2008 LY6 engine. Out came the stock pistons to allow access to the factory rings. Note the dual valve reliefs employed on this VVT application.02] The key to running big boost on a stock bottom-end is increasing the ring gap. We measured the factory ring gaps on the highmileage pistons after removal. The stock rings checked in at 0.019 inch (top) and 0.024 inch (bottom). These same rings were then re-gapped with a go/no-go minimum of 0.030 inch. We gapped the rings using this trick ring-gapping tool from Total Seal.03] The block was surfaced to ensure proper sealing under boost, then given a quickie ball hone and a fresh coat of black paint. The original stock LY6 crank was then reinstalled.04] The Gen 4 engines come with stronger connecting rods relative to the previous design. We torqued the rods according to the factory specs using the original, highmileage bolts.
01] Before adding boost, we ran the 6.0L in NA trim. Equipped with the turbo cam and Sniper intake, the TFS heads and Stage 3 cam propelled our 6.0L to 548 hp at 7,100 rpm and 462 lb-ft of torque at 5,500 rpm.02] Straight from the previous Gen 3Big Bang 6.0L, we reused the S475 BorgWarner turbos from Lil John’s Motorsport Solutions. Since they can support nearly 1,000 hp each, there was more than enough boost for the Gen 4 party.03] The bounty of boost was fed through this dual-core, air-to-water intercooler from CXRacing. We feared that we may have been getting near the flow and cooling limits of this inexpensive cooler, but it fit and worked well on our previous Big Bang test engines.04] Controlling boost was a pair of 45mm Hypergate wastegates from TurboSmart. Our eventual spring combination provided a minimum boost of 14.4 psi, which we raised with a manual boost controller to a maximum of 29.2 psi.
01] TurboSmart also supplied a Race Port blow-off valve to eliminate the pressure spike that occurs under lift-throttle conditions.02] We ran the turbo combination with a 92mm Holley Sniper throttle-body. Throttlebody sizing is less critical on turbo applications, as racers have made much more power breathing through a 92mm opening.03] Use of the stainless-steel turbo headers from DNA required some creative work with plug wires. We ran these Accel wires with ceramic boots where we could, but Westech’s Troy Goldie also whipped up a few extra-long plug wires to wrap under the headers.04] Using Holley’s HP ECU, we dialed in the 120-pound Holley injectors at each successive boost level. Starting at 14.4 psi, the 6.0L produced 1,078 hp, while 16.0 psi brought 1,150 hp and 1,213 hp at 17.5 psi. Pumping things up to 22 psi allowed the 6.0L to exceed the 1,300hp mark, with a peak of 1,349 hp. The next step up in boost to 26.6 psi unearthed almost 100 hp, with the power needle now registering 1,433 hp. The final run of the day (where we maxed out the 3-bar MAP sensor) crushed the 1,482hp mark set by our previous Gen 3 6.0L. With the boost gauge reading a full 29.2 psi (nearly 3 bar), the Big Bang Gen 4 6.0L threw down an incredible 1,543 hp and 1,256 lb-ft of torque.
Running 118-octane race gas and ice water through the intercooler core allowed us to get serious with the boost on this 6.0L. This graph shows the power curves at the various boost levels. Note that each successive jump in boost brought a subsequent increase to the power through most of the power curve. This is why turbo builds are so addictive. It is so easy to dramatically increase the power output, but take care not to get too greedy!
Here are the various boost curves associated with the power curves presented in Graph 2. Note that our oversized S475 turbos spooled up the same at each boost level; the difference in boost pressure came only after the desired pressure was reached. Each increase in boost brought a similar increase in power. Basically, the boost curves mirrored the torque curves. We stopped at 29.2 psi after topping out and damaging the 3-bar MAP sensor.
This is an interesting comparison, as it shows the power output of the 6.0L at 1 bar (NA), 2 bar (14.7 psi of boost), and 3 bar (29.4 psi, or as close as we could get to these boost levels). Run in NA trim (1 bar or atmospheric pressure), the 6.0L produced 548 hp at 7,000 rpm and 462 lb-ft of torque at 5,500 rpm. Adding an extra 1 bar of boost (actually 14.4 psi), the twin-turbo 6.0L produced 1,078 hp and 869 lb-ft of torque. Stepping up to nearly 2 bar of boost (3 bar total or 29.2 psi), the power output of the 6.0L skyrocketed to 1,543 hp.