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More on Squeezing a Supercharged LSA for Every Last 725 hp

Got PSI? Part II: The quest to max out a supercharged LSA small-block continues with a cam swap and some high-tech tuning tricks

Stephen Kim Aug 9, 2016 0 Comment(s)
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Of all the great things mankind has ever invented, factory boost ranks right up there with boneless chicken wings and free WiFi. Seriously, where would we be as a society if picking out bones impeded our march toward obesity and 4G data rates put the axe on playing Candy Crush at company meetings? While it’s tough to compete with perks that promote larger midsections and slacking off, factory boost makes huge horsepower gains so ridiculously easy that even the fattest and laziest of hot rodders can go fast.

The beauty of factory boost is that the OE’s pick up the tab for beefing up the short-block and cylinder heads for forced induction duty. Although the LSA shares the same dimensions as the 376ci naturally aspirated LS3 block, it ups the durability ante with cast-in (vs. pressed-in) cylinder liners, piston oil squirters and bulkheads that get a 20-percent increase in strength. Likewise, the LSA improves upon the LS3’s cast rotating assembly with a forged crank and powdered metal connecting rods. Up top, GM opted to cast the LSA’s cylinder heads from a higher-grade A356-T6 aluminum alloy (vs. 319-T5). By rotating the casting mold as the heads harden, GM significantly reduces porosity as well.

Long story short, the amount of R&D work GM invested in building a solid foundation for boost allows greedy hot rodders to pile even more boost on top of the factory pressure settings. Unlike many stock turbo four-bangers, whose compressors are already close to being maxed out at 14-plus psi, the LSA is boosted to just 8-9 psi from the factory. That conservative output, combined with the 1.9L capacity of the LSA’s blower, means that there are at least 5-6 more psi of fun left in the tank.

To show just how easy it is to pick up hundreds of horsepower in a factory boosted application, in Part 1 of this story we teamed up with the School of Automotive Machinists and Technology to wring every last air molecule we could out of a Chevrolet Performance LSA crate engine. After recording baseline numbers of 569 horsepower on SAM Tech’s SuperFlow engine dyno, we embarked on a long series of bolt-on mods by attacking the most easily accessible external components first, then working inward. The idea was to replicate the natural sequence of modifications as if the engine was bolted to a car’s framerails. The game plan called for bolting up a cold-air induction system and some long-tube headers before digging deeper with a 2.5-inch blower pulley, a Weapon-X ported blower snout and throttle body, an ATI 10-percent overdrive crank pulley, and DeatschWerks 1,500cc fuel injectors.

The results were downright staggering. Horsepower topped out at 725, while torque jumped to 736 lb-ft. That represented a 156hp gain over the baseline figures. Not too shabby at all for a few simple bolt-ons. For the next round of dyno thrashing, the only items left on the agenda were swapping out the cam to take advantage of the additional airflow, and searching for a few extra ponies by diving deeper into the fuel and timing maps. While this may seem rather straightforward on the surface, as SAM Tech clearly demonstrated, it’s much more complicated than meets the eye. Once the headers finally cooled back down the room temperature, the results were just as impressive as from the first phase of testing: an additional 99 hp from a cam swap, ported lower intake manifold, and EFI tuning.

Cylinder-to-Cylinder Tuning

Although the hp gains from the first round of LSA testing were impressive, SAM Tech Instructor Chris Bennett knew that uneven cylinder-to-cylinder airflow distribution was leaving some ponies on the table. This uneven distribution became far more detrimental as boost pressure increased. “On EFI engines with forward-facing throttle bodies the back cylinders (No. 7 and No. 8) usually run leaner than the rest of the motor. Sometimes you can design an intake manifold to compensate, but factory manifold designs are usually compromised by packaging considerations,” Bennett explains.

This puts tuners in an unenviable position of tuning for the weakest cylinder, which ultimately compromises power output. “Having wideband oxygen sensors mounted in each header primary allows us to monitor the air/fuel ratio of each cylinder. For a forced-induction engine like the LSA, our target air/fuel ratio is 11.9 to 12.5:1,” says Bennett. “The back cylinders were running about 0.7 points leaner than the rest of the motor. With the stock computer, we had raise the air/fuel ratio across the board, which means that the rest of the cylinders were now running too rich. If you can’t change the tune from cylinder to cylinder, the leanest cylinder always limits how aggressive you can get with the tune because it’s the most sensitive to timing.”

Inspecting the spark plugs revealed that the rear cylinders were not just running the leanest, but also the hottest. Instead of settling for an overly rich tune as a means of compensating for the lean cylinders, SAM Tech opted for a more practical solution. “The Holley Dominator EFI system allows adjusting the air/fuel ratio and timing of each cylinder individually. Once we hooked it up, we were able add more fuel to the back cylinders to cool them off,” Bennett recounts. “Cooling off the hot cylinders and pulling back the timing 1.5 degrees in those cylinders, allowed us to put more timing advance into the rest of the motor. These tuning changes resulted in a 20 hp increase, bringing the total to 745. That’s a considerable increase.”

With the tuning squared away, SAM Tech swapped out stock lower intake manifold for a ported unit from Weapon-X. This simple change bumped output up an additional 20 hp. With total hp now standing at 765, SAM Tech moved into the final phase of testing by swapping out the cam.

Roots vs. Centrifugal Cams

A blower cam is a blower cam, right? Not exactly. Both centrifugal and positive displacement blowers require additional cam duration to complement the increase in airflow they provide, as well as relatively wide lobe-separation angles to prevent the intake charge from leaking out the exhaust valve. However, sometimes slightly altering camshaft design can further complement the different ways that each style of blower goes about producing boost. Positive displacement blowers tend to produce boost early, with efficiency falling off at high rpm. In contrast, centrifugal blowers are lazy at low rpm, yet pile on the boost at high rpm.

Consequently, Comp Cams offers different camshaft grinds for positive displacement and centrifugal supercharger applications. “The idea is to tailor the torque curve of the engine to the supercharger’s boost curve. Positive displacement blowers can struggle with inefficiency at high rpm, so we add more intake duration to help counter this effect,” Billy Godbold of Comp Cams explains. “Centrifugal units are almost the exact opposite. They don’t make much boost at low rpm, so we close the intake valve earlier to make more cylinder pressure and power. These units are ultra-efficient and keep pulling at high rpm as long as we provide enough exhaust duration.”

For LS applications, Comp offers two very similar, yet slightly different, camshafts precisely for this purpose. The centrifugal blower grind (PN 54-477-11) checks in at 227/243-degrees of duration at 0.050, 0.614/0.624-inch lift and a 114-degree LSA. The positive displacement blower grind (PN 54-467-11) measures in at 239/243-degrees of duration at 0.050, with 0.624/0.624-inch lift and a 114-degree LSA. Both represent a big step up from the dinky 198/216-at-0.050 factory camshaft that picks the valves up just 0.492/0.480 inches. In theory, the differences in engine output between both of the Comp grinds should be subtle, but noticeable nonetheless. “You may only see a rather small change in output, probably less than 10 percent, at the far ends of the rpm range, but the trends would still be there,” Godbold surmises.

Of course, the big wildcard in the mix is the blower unit itself. While old-school 6-71 and 8-71 blowers can struggle to hit 50 percent adiabatic efficiency (a ratio of the ideal amount of work required to compress the air to the actual amount of work required to compress the air, or efficiency with which work is done), today’s positive displacement units improve upon that mark dramatically. Eaton claims that its sixth-generation supercharger units used on the LSA are 76 percent efficient. That is just as good as many centrifugal superchargers on the market. Eaton credits this bump in efficiency to a revised twin four-lobe rotor design that features a helix angle of 160 degrees intended to smooth out airflow while reducing drag. In contrast, the company’s fifth-generation rotors use 60 degrees of twist.

Given the enhanced efficiency of the sixth-generation Eaton blower, the Comp Cams team predicted that our LSA might react more like a centrifugal supercharged engine. They were right. Both camshafts produced 824 peak horsepower at 6,500 rpm, but the smaller cam posted a 5-7hp advantage throughout the entire rpm range. “A bigger blower that builds boost very early may have liked the bigger cam, but that small, super-efficient factory LSA blower reacted more like your typical centrifugal blower,” Godbold explains.

As expected, the results were subtle yet noticeable. Ultimately, the additional cam duration and lift dramatically increased the LSA’s output. Extending peak horsepower from 6,000 to 6,500 rpm also allowed spinning the blower faster, thus increasing boost to 13-14 psi. That netted an 59-horsepower increase from the cam swap alone.

Final Results

Throwing every bolt-on in the book at a Chevrolet Performance LSA, swapping cams, and fine-tuning the EFI calibration brought the final tally to 824 hp and 783 lb-ft of torque. That’s more than enough to run toe-to-toe with a healthy 540 big-block, while also knocking down 20 mpg, in a much lighter and more compact package. Sometimes, the demands of evolution simply favor a smaller, more efficient beast.

Charting the Gains
HP TQ
Baseline 569 573
Upper pulley 639 661
Ported snout 640 662
Ported TB 643 667
5% crank pulley 682 705
10% crank pulley 725 736
Holley EFI 745 768
Ported intake 765 763
Big cam 824 776
Small cam 824 783

Blower Efficiency
HP PSI HP/PSI
Stock 569 8 71
Modified 824 13 63

Chevrolet Performance Supercharged Blown Lsa 2/17

01. Set at just 8-9 psi from the factory, the stock LSA blower has plenty of boost left in the tank to support hundreds of additional hp. SAM Tech performed all testing on 93-octane pump gas.

Chevrolet Performance Supercharged Blown Lsa Parts 3/17

02. The beast that is the LSA was designed for hundreds of thousands of miles of trouble-free performance. Thanks to the aftermarket, anyone can take advantage of this durability and add over 250 hp without upgrading a single long-block component.

Chevrolet Performance Supercharged Blown Lsa 4/17

03. After compressed air exits the factory supercharger assembly, it’s routed through a circuitous path that rises upward through the intercooler core before the supercharger lid redirects it downward through the intake manifold runners. The goal of porting the intake housing is to minimize restrictions that can impede airflow and increase heat buildup along the way.

Chevrolet Performance Supercharged Intake Manifold 5/17

04. Boost is simply a measure of backpressure within the intake manifold. Improving airflow through the intake manifold can potentially decrease boost, which allows for making more hp before reaching the limits of pump gas. For $1,650, Weapon-X will port the stock lower intake manifold, throttle body and supercharger snout.

Weapon X Intake Manifold 6/17

05. The bottom of the Weapon-X intake manifold has been port-matched to the cylinder heads and radiused to smooth out airflow. In Round 1 of testing, the ported throttle body and blower snout netted a 4hp gain. In the second round of testing, the intake manifold was good for another 20 hp.

Dominator Efi 7/17

06. Granted that the factory PCM is an incredibly flexible unit when matched with powerful tuning software, the individual cylinder tuning capability of the Holley Dominator EFI system paid huge dividends on our LSA test engine. Richening up the two leanest cylinders and increasing ignition advance netted 20 hp over the stock PCM.

Chevrolet Performance Supercharged Lsa Results 8/17

07. Yet another variable when tuning a forced-induction engine is that both manifold pressure and voltage can affect fuel injector output. DeatschWerks provides a handy table so injector offset can be adjusted accordingly.

Two Comp Cams Blower Grinds 9/17

08. Experimenting with two Comp Cams blower grinds allowed tailoring cam specs to the boost curve of the LSA’s sixth-generation Eaton supercharger. The engine produced one additional psi of boost with the smaller cam, most likely due to its shorter intake duration.

Comp Cams Cam Swaps 10/17

09. Comp Cams makes cam swaps easy with its valvespring kits (PN 26926TS-KIT), which match the springs with the correct retainers, seats and locks for a given application. Comp set us up with dual 1.320-inch springs that feature 129 pounds of seat pressure and 470 pounds of open pressure.

Comp Cams Steel Retainers 11/17

10. Titanium is great for bragging rights, but for a 6,500-rpm engine, Comp Cams’ lightweight tool steel retainers (PN 1779-16) are more than up to the task. They’re 30-percent stronger than conventional chrome-moly retainers, and offer excellent wear resistance. We matched them up with Comp 7-degree locks.

Stock Pushrod 12/17

11. It doesn’t take much to bend a stock pushrod, so SAM Tech replaced them with a set of Hi-Tech chrome-moly units from Comp Cams. They measure 5/16-inch in diameter, while overall length checks in a 7.400 inches.

Lsm Racing Valvespring Removal 13/17

12. LSM Racing’s valvespring removal tool makes quick work of swapping out springs with the heads still attached to the engine. After bolting it to the rocker stands, a ratchet and socket are all that’s needed to compress the springs and remove the locks.

Chevrolet Performance Supercharged Blown Lsa Output 14/17
Chevrolet Performance Supercharged Blown Lsa Data 15/17
Chevrolet Performance Supercharged Dyno Results 16/17

13. As Comp Cams predicated, the difference in hp output between the two cams wasn’t dramatic, but noticeable nonetheless. The smaller cam simply worked better with the Eaton blower’s high-rpm efficiency while also bumping up mid-range torque thanks to its shorter intake duration.

Sam Tech Efi Tuning Class 17/17

14. Students of SAM Tech’s EFI Tuning class listen in closely as instructors Chris Bennett and Alex Peitz explain how to adjust the countless tuning maps associated with tuning a supercharged 824hp small-block. In addition to tuning for maximum power, students also learn how to tune for driveability in street/strip applications.

Sources

Comp Cams
Memphis, TN 38118
901-795-2400
http://www.compcams.com
ATI Performance Products
Baltimore, MD 21207
877-298-5039
www.atiracing.com
School of Automotive Machinists
Houston, TX 77055
713-683-3817
samracing
Holley
Bowling Green, KY 42101
866-388-5120
www.Holley.com
Chevrolet Performance
888-924-9147
www.chevroletperformance.com
DeatschWerks
Oklahoma City, OK 73106
405-217-0701
http://www.deatschwerks.com
Weapon-X Motorsports
www.weaponxmotorsports.com

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