There are many routes to increased performance. If we start with a stock motor, you can always upgrade the existing combination with a top-end kit featuring heads, cam and intake. If you want more, you can also increase the displacement of the short block. Of course there is always nitrous oxide, but if you are looking for serious power gains, nothing beats forced induction. Given the many forms of forced induction, the question is not do you or do you not choose boost, but which boost do you choose. Those looking for the absolute answer on which boost is best should look elsewhere, as the only true answer is “it depends”. Rather than focus on which one might be best, let’s focus on how awesome it is to have so many choices. The reality is that whether you choose a turbo, positive displacement or centrifugal supercharger, your combination really is Better With Boost.
To illustrate the power of positive thinking, we subjected an LS motor to boost from a Vortech centrifugal supercharger. Obviously there are countless LS combinations available and Vortech offers dedicated kits for many of the popular applications, but we chose to go a different route. Rather than run the test on a new Camaro or Corvette, we chose to go the wrecking-yard route. Nabbing a truck motor out of the local boneyard allowed us to not only demonstrate the benefits of boost, but do so at a more reasonable cost. Since 4.8L and 5.3L truck motors were built by the millions, they are both readily available and amazingly affordable. Not only that, they are also extremely capable, with plenty of performance potential just begging to be unleashed. Our test was run on a modified 4.8L truck motor, but boost can easily be applied to a bone-stock truck motor as well-though we highly recommend opening up the plug gap before running excess boost.
Stock will rock, but our 4.8L LR4 featured a few performance upgrades that allowed it to produce impressive power both normally aspirated and under boost. Remember, the power gains you make normally aspirated can be further multiplied under boost. If you run 15 psi like we did on this test, it is possible to nearly double the normally aspirated power gains so feel free to upgrade the motor before adding boost. During the rebuild, our 4.8L was first treated to a set of forged JE pistons to increase both strength and power. The slight dome offered an increase in static compression while the forged construction provided plenty of strength under boost. The remainder of the short block was box stock, including the block, crank and rods, though we upgraded the piston rings as well. The other power change we made to the short block was to replace the stock LR4 cam with a Stage 1 truck cam from Brian Tooley Racing. Perfect for the little 4.8L, the mild Stage 1 BTR truck cam offered .552 lift, a 212/218-degree duration split and 113-degree lsa.
Topping the modified 4.8L short block was a set of TFS Gen X 205 heads. The heads not only flowed significantly more than the stock 706 castings, but offered a spring package capable of keeping pace with the boost, cam lift and rpm potential of the supercharged combo. The TFS Gen X 205 heads were combined with the stock rockers and hardened pushrods from COMP Cams. Feeding the TFS-headed 4.8L was a stock truck intake and 78mm Accufab throttle body along with a set of 83-pound injectors from Holley. The injectors were chosen in anticipation of the elevated power levels of the supercharged combination. Also present was a Holley HP management system, 1 ¾-1 7/8-inch step headers and 5W-30 Lucas synthetic oil. After dialing in the air/fuel and timing curves, the 4.8L produced 398 hp at 6,300 rpm and 353 lb-ft of torque at 5,600 rpm. With our baseline out of the way, it was time for some boost.
For our test, Vortech supplied an LS kit that featured everything needed to apply boost to our 4.8L. Complete as usual, we applied only a portion of the supplied components in our test, including the self-contained V3 supercharger, mounting bracket (with tensioner) and aluminum discharge tube. As luck would have it, the 7.5-inch, ATI Super Damper run on a previous test with a Whipple supercharger lined up perfectly to drive the Vortech. All we had to do was mount the self-contained supercharger (required no oil drain hole in the pan), pop on and tighten the belt and then install the discharge tube complete with dedicated bypass valve.
The 83-pound injectors offered more than enough fuel to feed the supercharged beast, and after tuning, we were rewarded with some big numbers. The use of a 3.80-inch blower pulley put the peak boost pressure at 15.2 psi at 6,500 rpm. The elevated boost level brought serious power gains, as the little-supercharged 4.8L produced an amazing 699 hp and 565 lb-ft of torque. The rising boost curve meant that peak power and torque occurred at the same engine speed, so there was much more power to be had with more engine speed. Given the already elevated boost level, we will adopt intercooling before we attempt to make this combination even Better with (More) Boost.
The first thing you notice about the graph is that the supercharged power curve was still climbing rapidly at the 6,500-rpm shut off point. In fact, we had yet to reach the torque peak at that rpm, and the power peak would occur easy 1,000 rpm beyond that. The reason for this is the rising boost curve offered by the centrifugal supercharger. The increasing boost curve artificially increases the engine speed where the motor made peak power. Run in normally aspirated trim with the mild Stage 1 truck cam, the 4.8L produced 395 hp and 353 lb-ft of torque. After adding the Vortech supercharger to the mix, the peak numbers jumped to 699 hp and 565 lb-ft of torque. The pulley ratio used on the little 4.8L produced a peak of 15.2 psi of boost, which was too high for street use with pump gas. What this combination really needed was an intercooler.
Sources: Brian Tooley Racing; briantooleyracing.com, Holley/Hooker; holley.com; JE Pistons; jepistons.com, Lucas Oil;lucasoil.com, Trick Flow Specialties;trickflow.com, Vortech Superchargers;vortechsuperchargers.com