One of the greatest inventions since the introduction of the internal combustion engine has to be boost. Nothing adds power to a combination like the introduction of some positive pressure, especially when it comes from an efficient twin-screw supercharger like the one we tested from Kenne Bell. Adding modest boost to your engine will transform even the wimpiest LS powerplant. Heck, even boosting a stock engine will offer serious gains, but the real power comes from the combination of boost and performance mods. The very best supercharged engines have something in common, they all started out as powerful naturally aspirated combinations. The more power your engine makes in naturally aspirated trim, the more power it will make under boost. What better way to illustrate our naturally aspirated/boost theory than with the application of boost to a pair of different LS powerplants?
The idea was to run the two engines in naturally aspirated trim and then again after the application of boost from a Kenne Bell supercharger. The question we wanted to answer was would the difference in power in the naturally aspirated combinations carry over once we added boost? In other words, would the extra power of the bigger engine pay off or would the boost make up for the lower power numbers of the smaller engine? Naturally, we had to run both supercharged combinations at the same boost level, not to mention running the engines with the same air/fuel ratio, timing, and oil temperatures. Luckily, we had the perfect pair of test mules on hand. First up was a Chevrolet Performance LS3 crate engine supplied by Gandrud Chevrolet. Plenty impressive right out of the box, the factory 376-inch LS3 was augmented for our test with a cam and spring upgrade from Brian Tooley Racing. The single most popular upgrade for any LS, the right cam swap nets huge power gains, especially on an LS3 sporting serious head flow right from the factory. The cam upgrade supplied by Brian Tooley Racing was designed for a positive displacement supercharger by offering a 0.617/0.595-inch lift split, a 231/248-degree duration split, and a wide 120-degree LSA.
Test engine number two was more than a few steps up the performance ladder, as the 427 LSX engine featured more of everything, including cubes, cam, and cylinder head flow. Starting with an iron Chevrolet Performance LSX block (also from Gandrud Chevrolet), the 427 featured a Lunati 4.000-inch stroker crank teamed with Carrillo Bullet-series rods and CP pistons. Also present in the buildup was a Brain Tooley Racing Stage IV LS7 cam, a Moroso oiling system, and an adjustable ATI Super Damper. Topping the 427 was a set of Mast Black Label LS3 heads sporting 390 cfm flow capability. For this test, the 427 was run with a FAST LSXR induction system that included a Big Mouth throttle body, billet fuel rails, and FAST 75-pound injectors. The naturally aspirated LS3 shared these injectors, but the supercharged combos relied on 83-pound Holley units.
Run in naturally aspirated trim, the BTR-cammed LS3 produced 558 hp at 6,300 rpm and 512 lb-ft of torque at 4,800 rpm. The naturally aspirated 427 upped the ante to 651 hp at 6,400 rpm and 610 lb-ft of torque at 5,100 rpm. After establishing our naturally aspirated baselines, it was time for some boost.
Boost for our pair of LS3-headed test engines came from a Kenne Bell 2.8L, twin-screw supercharger. Designed for a 2010 Camaro application, the kit featured the polished blower, an air-to-water intercooler, and the requisite bypass valve. For the BTR-cammed LS3, the supercharger was configured with a 3.75-inch blower pulley and a stock 7.5-inch (truck) crank pulley. This combination produced a peak boost level of 7.9 psi at 6,600 rpm, where the supercharged LS3 managed 775 hp. Torque production from the boosted LS3 topped out at 643 lb-ft. There was plenty of power left in the combination but this test was designed to illustrate the relative changes in power so we yanked the blower off of the LS3 and installed it on the larger 427. It was necessary to adjust the pulley ratio on the larger engine to equalize the boost level between the two engines. This was accomplished with the installation of an 8.19-inch hub on the ATI Super Damper. This drive ratio resulted in a peak boost pressure of 7.7 psi and peak power numbers of 861 hp at 6,600 rpm and 714 lb-ft of torque. The difference in power naturally aspirated was 93 hp and once we added the supercharger, it dropped slightly to 86 hp. It is important to remember that number was with 0.2 psi less boost, so we are going to call this boost battle a draw. So, what’s the moral of this story? Any improvement you make to the base engine will pay off after you add boost to the mix and the larger engine will be able to make that power more efficiently since it won’t have to work the blower as hard as the smaller engine.
1. Rather than run just one engine with our Kenne Bell supercharger, we decided to compare two, starting with this 6.2L LS3 crate engine supplied by Gandrud Chevrolet.
2. The lone modification to the crate engine was a cam upgrade. In anticipation of boost, we installed a Stage 3 PD blower cam from Brian Tooley Racing. Designed specifically for a positive displacement supercharger, the Stage 3 stick offered a 0.617/0.595-inch lift split, a 231/248-degree duration split, and 120-degree LSA.
3. Dialing in the naturally aspirated and supercharged combinations was this Holley HP EFI management system.
4. Run in naturally aspirated trim, the BTR-cammed LS3 produced 558 hp at 6,300 rpm and 512 lb-ft of torque at 4,800 rpm.
5. The larger 427 LSX featured an iron block supplied by Gandrud Chevrolet. Internals for the block included a forged Lunati stroker crank, Carrillo Bullet-series rods, and CP forged pistons. Since boost was in the cards, we also utilized ARP head studs and Fel-Pro MLS head gaskets.
6. Topping the 427 was a set of Mast Black Label LS3 heads. The Mast heads featured 280cc intake ports that flowed 390 cfm.
7. Run on the dyno with a FAST LSXR intake, 102mm Big Mouth throttle body, and Holley 83-pound injectors the 427 produced 651 hp at 6,400 rpm and 610 lb-ft of torque at 5,100 rpm.
8. After running the two engines in naturally aspirated trim, it was time to apply boost from the Kenne Bell supercharger. Equipped with an air-to-water intercooler, the 2.8L twin-screw supercharger was easily capable of exceeding 1,000 hp at elevated boost levels.
9. To ensure adequate airflow to the supercharger, Kenne Bell supplied this massive 168mm throttle body.
10. The LS3 was configured with a stock (7.5-inch) truck crank pulley and 3.75-inch blower pulley. This combination produced a peak boost pressure of 7.9 psi at 6,600 rpm on the cam-only LS3.
11. Run in supercharged configuration, the BTR-cammed LS3 produced 775 hp at 6,600 rpm and 643 lb-ft of torque at a peak boost pressure of 7.9 psi (both power and boost were still climbing).
12. We then installed the same Kenne Bell supercharger onto the larger 427 LSX. How would the more powerful 427 perform at the same boost level?
13. To match the boost level run on the LS3, we installed this ATI Super Damper system that allowed us to swap the outer damper shell with ones of different diameters. We combined the 3.75-inch blower pulley with an 8.19-inch ATI crank pulley to equalize the boost pressure between the two engines.
14. The Kenne Bell supercharger was run on the dyno using a custom drive system that included a Meziere water pump, trick idler from Turn Key Engine Supply, and a fabricated bracket from Kenne Bell.
15. Run at a peak boost pressure of 7.7 psi, the 427 LSX produced 861 hp at 6,600 rpm and 714 lb-ft of torque.
Cam-Only LS3 vs. 427 LSX - NA
As powerful as a cam-only LS3 can be, it was not really surprising that the larger and wilder 427 LSX produced more power. Equipped with the dedicated Stage 3 (PD) blower cam from Brian Tooley Racing, the naturally aspirated LS3 crate engine produced 558 hp at 6,300 rpm and 512 lb-ft of torque. The Mast LS3-headed 427 stepped things up to 651 hp at 6,400 rpm and 610 lb-ft of torque. Run with the FAST LSXR intake, the 427 made nearly 100 horsepower more than the smaller (BTR-cammed) LS3.
Cam-Only LS3 vs. 427 LSX - Kenne Bell Supercharged (7.9 psi)
After installation of the Kenne Bell supercharger, the cam-only LS3 produced 775 hp at 6,600 rpm and 643 lb-ft of torque at a peak boost reading of 7.9 psi. Both the power and boost were still climbing at our shut-off point of 6,600 rpm. Run with the Kenne Bell supercharger (at a peak boost of 7.7 psi at 6,600 rpm), the 427 produced 861 hp at 6,600 rpm and 714 lb-ft of torque. Equalizing the boost on the larger 427 required a change in blower-to-crank pulley ratio, but the power gains remained pretty consistent from NA to supercharged.
Kenne Bell Supercharged 427 LSX (7.7 psi vs 10.6 psi)
Obviously, 7.7 psi is not a lot of boost for a 427 LSX engine. All of the forged components were designed to handle a lot more power and boost, so we performed a couple of pulley swaps. After installation of the 3.375-inch blower pulley (running the same 8.19-inch ATI crank pulley), the boost increased to a peak of 10.6 psi. The increased boost pressure pushed the peak power numbers up to 957 hp and 780 lb-ft of torque. There was plenty more left in the 2.8L blower (and combination), but we ran out of blower pulleys and available dyno time.