Text and Photos: Richard Holdener

In the LS family, the 4.8L occupies the bottom of the displacement hierarchy. With the smallest bore and shortest stroke of the lineup, it is consistently overlooked in favor of the 5.3L, 6.0L, and 6.2L variants. Displacement delivers natural torque advantages and allows larger bores to improve cylinder head flow. The 4.8L has neither of those working in its favor.

That changes with forced induction. Add boost to a modified 4.8L, and the power output closes the gap rapidly. This is especially true with a centrifugal supercharger, where the elevated rpm capability of a modified small-displacement engine generates proportionally more boost.

The Multiplier Principle

Boost functions as a multiplier. A naturally aspirated engine already operates under atmospheric pressure (14.7 psi at sea level). Supplying 14.7 psi of boost from a supercharger theoretically doubles the power output, minus parasitic losses from driving the blower. The critical variable is the NA starting point: doubling a 300 hp combination yields 600 hp, but doubling a 400 hp combination yields closer to 800 hp from the same boost pressure.

This understanding is what drove the decision to modify the 4.8L before installing the supercharger.

Building the 4.8L Foundation

The 4.8L test engine retained the stock iron block and crank. Speedmaster rods were paired with JE forged pistons featuring 7cc domes to increase static compression while providing strength for supercharged duty. ARP head studs, new Fel-Pro MLS head gaskets, fresh Speed-Pro bearings, and Total Seal rings completed the short-block.

The COMP 273LR cam, mild by 6.0L standards, proved well-suited for the smaller 4.8L displacement. It offered a 0.610/0.617-inch lift split, a 223/231-degree duration split, and a 112-degree LSA.

CNC-ported TFS GenX 205 heads provided enhanced breathing. The 205 heads were sized specifically for the smaller-bore LS applications, flowing substantially more than the factory 706 castings.

A dual-plane, carbureted Edelbrock Performer RPM intake topped the TFS GenX heads, fed by a 750-cfm Holley HP carburetor. An MSD ignition controller handled timing, a Meziere electric water pump managed cooling, and long-tube headers completed the exhaust.

ATI supplied a 7.50-inch Super Damper. Combined with a 3.80-inch blower pulley and the elevated engine speed of the modified 4.8L, the setup produced a peak boost level of 15.8 psi.

Naturally Aspirated Baseline

On the dyno in naturally aspirated trim, the modified 4.8L produced 438 hp at 7,000 rpm and 351 lb-ft of torque at 5,800 rpm. The cam and heads dramatically extended the effective operating range of the small-displacement engine.

The MSD ignition controller plugged directly into the factory coil packs and sensors, allowing precise timing curve adjustments for both the NA and boosted configurations.

Adding the Vortech Ti Supercharger

The Vortech Ti supercharger was selected for this build. Capable of supporting over 1,000 hp on the right application, the Ti had more than sufficient capacity for the 4.8L. Vortech supplied mounting brackets, a tensioner, and a dedicated aluminum discharge tube designed for an EFI LS application.

A 3.80-inch, 8-rib blower pulley was paired with the ATI Super Damper. The fixed tensioner and idler maintained consistent belt tracking under load.

For this carbureted configuration, custom cold-side tubing was fabricated to route boost through an air-to-water intercooler and into a CSU (Carburetor Solutions Unlimited) blow-through carburetor bonnet. The CSU-modified Holley 850 featured adjustable, boost-referenced power valves designed specifically for blow-through applications.

At elevated boost levels, inlet air temperatures become a concern. A CXRacing air-to-water intercooler, tested to over 1,000 hp, reduced inlet temps by 86 degrees. A Turbosmart Race Port blow-off valve was integrated into the intercooler tubing.

The CSU blow-through carburetor: a modified Holley 850 with boost-referenced power valves calibrated for pressurized induction.

The CSU carb bonnet routed pressurized air from the blower, through the intercooler, and into the carburetor.

Supercharged Results

After jetting adjustments and boost-referenced power valve calibration, the supercharged 4.8L produced 799 hp and 608 lb-ft of torque at 6,900 rpm. That peak torque and peak horsepower occurred at the same engine speed indicates the combination had not yet reached its power ceiling. Both boost and power were still climbing at shutdown.

The torque curves tell the full story. On the naturally aspirated 4.8L, peak horsepower and peak torque were separated by 1,200 rpm. Under boost, both peaks converged at 6,900 rpm, confirming the supercharger was still building pressure and the engine had additional capacity. A 361 hp gain from a single supercharger installation on a properly prepared foundation.

What the Data Shows

The 4.8L moved from 438 hp naturally aspirated to 799 hp under 15.8 psi of boost. The combination was still climbing at shutdown. The results confirm the multiplier principle: building a strong NA foundation with forged internals, the right cam, and properly sized heads allows boost to deliver its full potential, even from the smallest displacement in the LS family.