Text & Photos: Richard Holdener
In the LS world, the little 4.8L is the Rodney Dangerfield of the bunch. Because of its size it just gets no respect. Even the 5.3L—just 0.5 liters larger—gets all the press, to say nothing of the 6.0L and 6.2L variants. True enough, there is much to be said for displacement, both for its natural torque production and the bigger bore’s ability to improve cylinder head flow. By contrast, the diminutive 4.8L suffers from both the smallest bore and the shortest stroke of the LS family. The minimal displacement might be beneficial for fuel mileage, but power production definitely suffers compared to its larger siblings. Even with the usual bolt-on modifications like cylinder heads, cams, and intakes, the 4.8L will always take a backseat to the larger LS engines unless you apply the great equalizer known as boost. Add boost to a 4.8L, particularly to a modified one, and just watch that power needle swing. This is especially true of a centrifugal supercharger (like our Vortech), where the extra rpm offered by a modified 4.8L means plenty of extra boost.
To illustrate how well the great equalizer actually works, we subjected a 4.8L to some reasonably serious boost levels from a powerful Vortech Ti supercharger. Before adding the positive pressure, we augmented the combination both to help it increase and withstand the extra cylinder pressure. Boost works like a multiplier since a naturally aspirated engine operates under pressure already— atmospheric pressure, that is (of 14.7 psi at sea level). If we double that pressure by supplying the engine 14.7 psi of boost from a supercharger we can theoretically double the power output. Of course, we need to subtract the parasitic losses associated with driving the supercharger (there is no free lunch), but the gains offered by boost are nothing short of amazing, regardless of the starting point. The thing to remember is that the more power the engine makes naturally aspirated, the more it will make under pressure. Doubling the power output of a mild, 300hp combination might yield 600 hp, but applying the same amount of boost to a 400hp version can yield closer to 800 hp.
The 4.8L test engine consisted of a stock iron block and crank, and Speedmaster rods augmented with a set of JE forged (7cc dome) pistons. Since boost was in the cards, we also installed ARP head studs and new Fel-Pro MLS head gaskets.The JE forged pistons featured asymmetrical skirts designed to decrease friction and improve power without sacrificing ring seal or strength.
A clear understanding of this phenomenon is what drove us to modify the 4.8L before the installation of the Vortech Ti supercharger. Starting with a 4.8L block, we retained the factory crank but added a set of JE forged pistons, Speedmaster rods, and Total Seal rings. The 7cc domes both increased static compression while providing a stouter piston to better withstand the supercharged power. Balancing and machining were combined with fresh Speed-Pro bearings, Fel-Pro gaskets, and ARP head studs to create a stout short- block. The trio of power producers included a Comp 273LR cam, TFS GenX 205 heads, and an Edelbrock Performer RPM intake. The Comp cam offered a 0.610/0.617-inch lift split, a 223/231-degree duration split, and a 112-degree LSA. The 205 heads were designed specifically for the smaller-bore LS applications but owed substantially more than the factory 706 heads. Topping the TFS GenX heads was a dual- plane, carbureted RPM intake from Edelbrock with a 750-cfm Holley HP carburetor. Finishing touches included an MSD ignition controller, Meziere electric water pump, and long-tube headers. Run on the dyno in this con guration, the modi ed 4.8L produced peak numbers of 438 hp (at a lofty 7,000 rpm) and 351 lb-ft of torque at 5,800 rpm.
Though mild for a 6.0L (or larger) combination, the Comp 273LR cam was plenty wild for the little 4.8L.
Enhanced breathing for the 4.8L came from a set of CNC-ported TFS GenX 205 heads. The 205 heads were sized perfectly for the small-bore 4.8L.
ATI supplied this 7.50-inch Super Damper for our supercharged 4.8L. When combined with the 3.80-inch blower pulley and elevated engine speed, the combo provided a peak boost level of 15.8 psi.
Rather than run the 4.8L in injected form, we selected this dual-plane, carbureted Performer RPM intake.
This MSD ignition controller handled ignition chores for the 4.8L. We liked the easy hookup, as the controller plugged right into the factory coil packs and sensors. The MSD allowed us to dial in the timing curve on both the NA and boosted LS con gurations.
The great equalizer takes many forms, but for our test it was a Vortech Ti supercharger. Though Vortech offered the self-contained V3 supercharger that required no oil drain in the pan, we chose the Ti trim for this test. Vortech also supplied the necessary mounting brackets, tensioner, and dedicated aluminum discharge tube designed for an EFI LS application. For our carbureted combo, we chose to design our own cold-side tubing, complete with intercooler and blow-off valve. Truth be told, Vortech offers a carb bonnet but we relied on a CSU (Carburetor Solutions Unlimited) blow-through carburetor for this test, so we gured it was only proper that we run their carb bonnet. The Vortech blower kit allowed us to put the ATI Super Damper to good use by combining it with a 3.80-inch blower pulley. The combination netted a peak boost reading from the blower of 15.8 psi. Given the elevated boost level, we installed an air-to-water intercooler we had on hand from CXRacing. Tested at over 1,000 hp, the core brought inlet air temps down by 86 degrees. The intercooler tubing was also con gured with a Turbosmart Race Port blow-off valve. After minor jetting and adjustments to the boost-referenced power valves, the supercharged 4.8L produced 799 hp and 608 lb-ft of torque. If you’ve got a 4.8L and are looking for an extra 361 hp, look no further than the great equalizer.
Run on the dyno (in naturally aspirated trim) with the dual-plane Edelbrock Performer RPM intake and 750-cfm Holley HP carb, our forti ed 4.8L produced peak numbers of 438 hp (at 7,000 rpm) and 351 lb-ft of torque (at 5,800 rpm). The cam and heads dramatically increased the effective operating range of the little 4.8L. 
Though Vortech offers a number of blowers sized to work well on the 4.8L, we chose the Ti trim. Capable of supporting over 1,000 hp on the right application, the Ti was more than enough blower for the 4.8L.
From our handful of blower pulleys, we selected a 3.80-inch, 8-rib pulley for this test. Note the idler and fixed tensioner employed on the Ti trim.
Knowing that with elevated boost comes higher inlet air temps, we installed this air-to-water intercooler in the system. Ambient dyno water was fed through the core during testing.
Naturally, our supercharged 4.8L required a suitable blow-through carburetor. We contacted the guys at CSU for one of their modi ed Holley 850s. Designed by CSU speci cally for blow-through applications, the CSU carb featured adjustable, boost-referenced power valves.
Feeding boost from the blower, through the intercooler, and into the carburetor was this CSU carb bonnet.
Run on race gas with the Vortech Ti supercharger, the carbureted 4.8L produced 799 hp at 6,900 rpm. That the torque peak occurred at the same engine speed means we were actually nowhere near the real power peak, as the boost and power were still climbing rapidly.
What happens when you add boost from a centrifugal supercharger? You get some serious power gains, that’s what. The 4.8L was rst modi ed with forged JE pistons, a Comp cam, TFS GenX 205 heads, and an Edelbrock Performer RPM intake and a Holley 750 carb induction system. This combination produced 438 hp at 7,000 rpm. After installation of the Vortech Ti-trim supercharger, the power output jumped dramatically to 799 hp at 6,900 rpm. The power (and boost) curves were rising rapidly, but we shut the party off at 6,900 rpm.
The torque curves tell the real story of the combination, as the supercharged 4.8L produced peak torque (and peak hp) at the same 6,900 rpm. On the naturally aspirated 4.8L, peak horsepower and peak torque were separated by 1,200 rpm. We could only dream of revving this engine successfully to 8,200 rpm with the Vortech, but rest assured there was plenty of power left in the supercharger and this 4.8L combination.