The Premise

A fundamental principle in forced induction holds that the more power an engine produces naturally aspirated, the more it will produce under boost. To put that theory to a measurable test, we ran two LS-platform engines - a 376ci LS3 and a 427ci LSX - through identical conditions on the dyno, first without boost, then with a Kenne Bell 2.8L twin-screw supercharger.

The goal was straightforward: establish naturally aspirated baselines, apply the same boost level to both engines, and measure whether the power gap held.

The Two Test Engines

The first engine was a Chevrolet Performance LS3 crate engine supplied by Gandrud Chevrolet. Its single modification was a Stage 3 positive displacement blower cam from Brian Tooley Racing, offering a 0.617/0.595-inch lift split, 231/248-degree duration split, and a wide 120-degree LSA - purpose-selected for supercharged applications.

The second was a 427ci LSX built on an iron Chevrolet Performance LSX block (also from Gandrud Chevrolet). Internals included a Lunati 4.000-inch stroker crank, Carrillo Bullet-series rods, and CP pistons. A Brian Tooley Racing Stage IV LS7 cam handled valve events, while a set of Mast Black Label LS3 heads delivered 390 cfm of intake flow. A Moroso oiling system and adjustable ATI Super Damper completed the rotating assembly. Both engines ran with FAST LSXR induction systems featuring Big Mouth throttle bodies, billet fuel rails, and FAST 75-pound injectors in naturally aspirated trim, switching to 83-pound Holley units under boost.

Naturally Aspirated Baselines

The BTR-cammed LS3 produced 558 hp at 6,300 rpm and 512 lb-ft of torque at 4,800 rpm. The 427 LSX raised that to 651 hp at 6,400 rpm and 610 lb-ft of torque at 5,100 rpm - a difference of 93 hp between the two platforms.

The 6.2L LS3 crate engine from Gandrud Chevrolet - the smaller of the two test platforms.

The Stage 3 PD blower cam from Brian Tooley Racing: 0.617/0.595-inch lift split, 231/248-degree duration split, and 120-degree LSA. Selected specifically for positive displacement supercharger applications.

A Holley HP EFI management system handled tuning across all naturally aspirated and supercharged configurations.

Naturally aspirated baseline: the BTR-cammed LS3 produced 558 hp at 6,300 rpm and 512 lb-ft of torque at 4,800 rpm.

The 427 LSX iron block from Gandrud Chevrolet, assembled with a Lunati stroker crank, Carrillo Bullet-series rods, CP forged pistons, ARP head studs, and Fel-Pro MLS head gaskets.

Mast Black Label LS3 heads with 280cc intake ports flowing 390 cfm.

The 427 LSX on the dyno with a FAST LSXR intake, 102mm Big Mouth throttle body, and Holley 83-pound injectors: 651 hp at 6,400 rpm, 610 lb-ft of torque at 5,100 rpm.

Under Boost: Kenne Bell 2.8L Twin-Screw

Boost came from a Kenne Bell 2.8L twin-screw supercharger originally designed for a 2010 Camaro application. The kit included a polished blower housing, an air-to-water intercooler, and a bypass valve.

On the LS3, a 3.75-inch blower pulley paired with a stock 7.5-inch truck crank pulley produced a peak of 7.9 psi at 6,600 rpm. The result: 775 hp and 643 lb-ft of torque - with both power and boost still climbing at the shut-off point.

To equalize boost on the larger-displacement 427, the crank pulley was swapped to an 8.19-inch ATI Super Damper hub. This produced a matched peak of 7.7 psi and delivered 861 hp at 6,600 rpm and 714 lb-ft of torque.

The Kenne Bell 2.8L twin-screw supercharger with air-to-water intercooler - rated well beyond the boost levels used in this test.

Kenne Bell's 168mm throttle body ensured adequate airflow to the supercharger inlet.

The LS3 pulley configuration: stock 7.5-inch truck crank pulley and 3.75-inch blower pulley, producing 7.9 psi peak boost at 6,600 rpm.

Supercharged LS3 result: 775 hp at 6,600 rpm, 643 lb-ft of torque at 7.9 psi peak boost. Both power and boost were still climbing at shutdown.

The same Kenne Bell supercharger transferred to the 427 LSX for the second half of the comparison.

An ATI Super Damper with interchangeable outer shells allowed precise pulley ratio adjustment. The 3.75-inch blower pulley paired with an 8.19-inch ATI crank pulley equalized boost between engines.

The dyno drive system: a Meziere water pump, Turn Key Engine Supply idler, and fabricated Kenne Bell bracket.

Supercharged 427 LSX result: 861 hp at 6,600 rpm, 714 lb-ft of torque at 7.7 psi peak boost.

Comparing the Results

Naturally Aspirated: LS3 vs. 427 LSX

The naturally aspirated gap was clear. The BTR-cammed LS3 produced 558 hp and 512 lb-ft. The Mast-headed 427, running a FAST LSXR intake, delivered 651 hp and 610 lb-ft - nearly 100 hp more from the larger, higher-flowing combination.

Supercharged: LS3 vs. 427 LSX at Matched Boost

Under boost, the LS3 reached 775 hp and 643 lb-ft at 7.9 psi. The 427 produced 861 hp and 714 lb-ft at 7.7 psi. The naturally aspirated delta of 93 hp held within 7 hp under boost (86 hp), even with the 427 running 0.2 psi less. The power gap carried over.

427 LSX: 7.7 psi vs. 10.6 psi

With the forged internals designed for higher loads, a pulley swap to a 3.375-inch blower pulley (same 8.19-inch ATI crank pulley) pushed the 427 to 10.6 psi. The result: 957 hp and 780 lb-ft of torque - with capacity remaining in both the 2.8L blower and the combination.

What the Data Shows

The naturally aspirated power advantage of the 427 carried over under boost with near-identical consistency. Every improvement made to the base engine - displacement, head flow, cam profile - paid dividends once boost was applied. The larger engine also achieved its numbers more efficiently, requiring less work from the supercharger to reach the same pressure.

For any build where forced induction is the end goal, the data reinforces a clear path: build the strongest naturally aspirated foundation first. The boost multiplies what is already there.