In today's high-performance world it is not uncommon to read about outrageous street machines that knock off 700-plus rwhp, produce 20-plus mpg, and pass emissions. Maybe we've been jaded but those results are almost standard requirements in any serious LS engine combination. A large part of the success is due to the quality of superchargers as well as the camshaft technology, PCM tuning, and many other little parts and pieces that make it all happen when the money is on the line. In this issue we are taking a look at two different superchargers and how it relates to the PCM. We made the run up to Redline Motorsports (Schenectady, New York) to follow as it changed from a Magnuson TVS 2300 supercharger to a Kenne Bell 2.8L on a 427ci LS3. Head honcho, Howard Tanner, set both superchargers to produce a peak boost reading of 14-15 psi and as you will see, despite the same boost levels, the PCM needed to be re-calibrated.
Our test subject is a '10 Camaro that has a bit of history behind it. The car is a test mule for all sorts of projects at Redline Motorsports. The '10 Camaro SS began as a bolt-on car and has progressed into a serious street machine. Its most notable mission was the pioneering model for the HTR series of cars sold through DeNooyer Chevrolet. But the latest endeavor for this supercharged LS-powered Camaro is its role as R&D tool for the forthcoming Motion Performance Fantastic Five re-launch. The engine appearing on these pages is a hint as to what's to come in the most powerful package for the Motion Performance cars--Phase III 427. But Tanner had to do his homework to get the estimated 800 hp from the 427 LS3, and switching to the larger Kenne Bell 2.8L supercharger system was part of the plan. The engine had to be reliable because DeNooyer Chevrolet backs each HTR and Motion Performance vehicle with a warranty.
In its current trim the 427 LS3 cranked out 712 rwhp with the Magnuson TVS 2300 and the goal was to get the R&D engine up to 800 rwhp reliably. That will allow Tanner to back it off for the 800-flywheel hp goal of the Phase III 427 model. Making the task more difficult, the goal to keep the boost limited to no more than 15 psi--like the HTR-750 package. The Redline 427 is a stout foundation as Tanner starts with a brand-new LS7 engine block to achieve the aforementioned size, matching it with a forged steel crankshaft, forged H-beam rods, and custom forged pistons. Up top, Redline adds CNC-ported LS3/L92 heads, custom camshaft (.646/.647-inch lift, duration of 230/242 at .050-inch lift, and 117-degree lobe separation), American Racing Headers long-tubes and three-inch X-pipe, and Borla mufflers. It all adds up to a 1,000-hp rating if someone was brave enough to add race fuel, up the boost to over 20 psi, and crank the ignition timing.
"Our goal was to change the power curve for more top-end power. The Magnuson has a ton of airflow down low and it shows in the curve. It makes huge torque down low, but the boost starts to drop off as the rpm climb. The horsepower still increases with RPM, but we wanted to get more higher RPM horsepower," commented Tanner as he explained the switch in supercharger systems. Running the same boost levels, unfortunately, didn't mean this was just a bolt-on and go scenario. The Kenne Bell 2.8L install changed several key components in the tuning realm--namely the MAF sensor readings and fuel injector sizing. The Kenne Bell 2.8L was designed for huge power and that meant Tanner had to go back in the PCM, using EFI Live software, to make adjustments.
First order of business was the change in fuel injector sizing--both sets of injectors were 63.5 lb/hr at a 3-bar rating (43.5 psi) and in the LS application these injectors are labeled as 74.75 lb/hr at 4 bar (58-60 psi). The difference was in the physical size. The Kenne Bell manifold utilizes the tall style injector while the Magnuson accepts the short one. "Part of the reason for a new calibration is that an injector is an electrical device with windings inside so the taller injector has longer reaction time to the PCM's command," inserted Tanner. He continued, "there are three tables to be adjusted in the PCM--injector flow correction table (or injector offset table), minimum injector pulse width, and small pulse adjustment."
The injector flow correction table offsets the injector timing using battery voltage and manifold pressure. The minimum injector pulse width deals with controlling the injectors at idle and part throttle. In the early days of EFI tuning it was hard to get large injectors, like the ones we used here, to idle properly without loading up with fuel. This table allows Tanner to get large injectors to pulse properly at idle and not load up with fuel. The final table is the small pulse adjustment. It controls the On-Time portion of firing the fuel injectors, and when going from a tall style injector to a short one, this table will control it between zero and four milliseconds. It has to do with the short injector having less wire wrap inside the body so the voltage travels quicker through it than the tall injector. According to Tanner, this table deals strictly with start-up, idle, and cruising as it's about drivability and not about WOT power.
Another area Tanner adjusted was the MAF sensor reading and this solely had to do with how Kenne Bell builds its systems. "We looked at what the competition was doing and we knew we had to be different," commented Jim Bell of Kenne Bell. He continued to tell us that all the Camaro systems feature an inlet system capable of supplying enough air for 1,200 rwhp. That means a massive inlet elbow to the back of the supercharger, 4.5-inch inlet piping, and an air filter mounted low and in a high-pressure area. Bell credits the company's chassis dyno testing with the hood closed and this system is worth 30 rwhp over one that uses a factory style airbox or cold-air kit. The change in inlet pipe diameter and MAF sensor placement means that a custom tune is required. According to Tanner, at initial start-up after the swap, EFI Live showed the MAF sensor was 18 percent off at idle and bouncing around from rich to lean at part-throttle. He made some adjustments and part-throttle tuning changes before going wide-open throttle.
On the dyno, the Magnuson logged a peak reading of 14.8 psi from 2,000 rpm to 3,700 rpm and it fell off to 13.2 psi by the time the engine reached the 6,000-rpm redline. It took a few different supercharger pulley sizes to achieve similar peak boost readings with the Kenne Bell 2.8L. The first pulley size was 3.50 inches and it produced an average boost of 9 psi with a peak reading of 10.6 psi. That resulted in a 710 rwhp and 651 lb-ft of torque. Next up was the 3.25-inch pulley and it increased boost to 13.2 psi peak and 11.6 average. It brought output up to 760 rwhp and 704 lb-ft of torque. The final pulley was a 3.00-inch puck that jumped the peak boost to 14.8 psi while maintaining an average of 12.6 psi through the curve. It was exactly what Tanner was hoping to accomplish--796 rwhp with 750 lb-ft of torque.
Tanner concluded, "the twin-screw Kenne Bell 2.8L doesn't make as much low-end torque as the Magnuson but it has more airflow through the higher rpm range. That shifts the power curve and carries the torque out longer as well as greater peak horsepower." And with 796 rwhp on tap, the Redline '10 Camaro is sure to be a threat to anything that lines up against it.
Kenne Bell 2.8L with 3.50-inch blower pulley*
|Average Boost||9 psi|
|Peak Boost||10.6 psi|
|Inlet Air Temps||93-120 degrees|
|Max MAF hertz||10,210|
|Injector Duty Cycle||82%|
Kenne Bell 2.8L with 3.25-inch blower pulley*
|Average Boost||11.6 psi|
|Peak Boost||13.2 psi|
|Inlet Air Temps||91-133 degrees|
|Max MAF hertz||10,540|
|Injector Duty Cycle||86% (needs 80 lb/hr injector)|
Kenne Bell 2.8L with 3.00-inch blower pulley*
|Average Boost||12.6 psi|
|Peak Boost||14.8 psi|
|Inlet Air Temps||89-136 degrees|
|Max MAF hertz||10,635|
|Injector Duty Cycle||98% (needs 80 lb/hr injector)|
*All testing was done using 93-octane pump gas.
Inside the Kenne Bell Twin-Screw Supercharger"We started manufacturing twin-screw superchargers in 1990," said Jim Bell of Kenne Bell Superchargers. The company's history dates back to 1968 when Bell opened shop specializing in Buick performance engines. The twin-screw business came when the company designed a supercharger system for the 5.0L Mustang back in 1990. Today, the company focuses solely on supercharger systems for late-model cars from the Big Three manufacturers.
Kenne Bell offers three different sizes for the 2010-present Camaro SS2.8L, 3.6L, and 4.2L--and according to Bell the unique feature of the superchargers is the inlet system. It is designed to flow enough airflow to support 1,200 rwhp in any of the three Camaro kits--depending on the throttle body restriction. Starting with the air filter, it is positioned outside of the engine bay in a high-pressure area. Chassis dyno testing with the hood down has resulted in a 30-rwhp gain over an air filter in the stock location. The air moves toward the throttle body inside a 4.5-inch (or 114 mm) tube, where the MAF sensor is located. If the stock throttle body is utilized, which is 90 mm, then airflow is restricted to just 1,147 cfm. Moving up to the Kenne Bell 110mm throttle body increases airflow to 1,710 cfm. The area behind the throttle body is a large plenum that makes a gradual bend to feed the air-hungry 4x6 billet aluminum rotors.
One unique aspect to the Kenne Bell twin-screw superchargers is the newly patented Liquid Cooled feature. Liquid is pumped through the supercharger unit to help lower operating temperatures, keeping the system efficient as that will lower inlet air temperatures for more power. Another aspect of the Camaro supercharger kit is the low parasitic losses from turning the supercharger. Bell told us they utilize a special blower drive system to test the superchargers to ensure it takes less power to turn a Kenne Bell unit than it does other positive displacement system on the market. The less power it takes to turn the supercharger translates to more power at the crankshaft. The concept is sort of like robbing Peter to pay Paul; you give up some power to turn the supercharger because the gains from the manifold pressure are far above what is needed to turn it.
There are three sizes, and remember, the biggest isn't always the better one for your application. Tanner did a casual comparison of two identical engine combinations--the Redline 427 used in this story relied on a Kenne Bell 2.8L supercharger while an identical package had a Kenne Bell 3.6L blower on top. Tanner had both superchargers huffing 10 psi peak boost into the engines. The 3.6L unit made more low-end power thanks to the greater air it moved per rotor revolution, but it fell short of the 2.8L in the upper rpm range710 rwhp for the 2.8L and the 3.6L rolled out 689 rwhp. Why? It is simple, under 15 psi of boost the 2.8L requires less hp to spin, which according to our results is a mere 21 less rwhp. Jim Bell concurred and said that under 15 psi of boost, the 2.8L unit is a better choice, but once you go over that the larger supercharger will make more power per pound of boost. In other testing with a Brand X engine the 3.6L made 73 more rwhp at 23 psi of boost over a 2.8L--proving that selecting the properly sized supercharger for the application is important.