F-3R-139
Here’s a typical bolt-on ProCharger system on a fifth-generation Camaro SS. As with Vortech superchargers, ProCharger’s larger compressors are mostly interchangeable with the bracketry, allowing custom combinations. Proper tuning is paramount when using a high-boost, large-displacement compressor, as is the durability of factory engine parts.
ProCharger’s large compressors and cog-style belt-drive systems are designed for racing applications, and several compressors are capable of 40 pounds of boost or more. It is these big blowers that are giving some turbo systems a run for their money in drag racing. This is ProCharger’s F3R compressor.
It is worth reviewing the complete compressor lineups from Vortech and ProCharger before investing in a bolt-on kit or a stand-alone setup for a custom engine project. Take the time to compare their respective performance traits and match them to the goals of your project.
Kit and Cost Considerations
Unlike turbocharger systems, there are a great number of bolt-on blower kits designed to work on stock LS engines. The number of kits changes constantly as new vehicle models are introduced and supercharger manufacturers and other aftermarket companies develop kits for them. For Roots-type systems, Magnuson’s kits cover most popular LS-powered vehicles. When it comes to twin-screw systems, there are few choices for vehicles with rectangular-port heads; most are designed for earlier, cathedral-port engines (LS1, LS2, and LS6). Vortech’s new twin-screw blower is offered in kit form for the rectangular-port LS3 engine of the Camaro and G8 GXP with more applications expected.
To ensure pump-gas compatibility and to lower the risk of detonation, bolt-on kits typically make less than 10 pounds of boost and deliver around 80 to 125 additional horsepower with preprogrammed tuning. Greater performance is attainable with custom tuning, smaller-diameter pulleys, and the like, but such changes increase the risk of detonation on stock engines with high compression ratios and cast rotating parts.
Of course, cost is an important factor for any enthusiast selecting a supercharger kit. One of the important factors in the centrifugal supercharger’s favor is generally a lower purchase cost in kit form when compared with Roots/screw kits. That’s because the ability to mount the compressor head unit almost anywhere allows manufacturers to bundle most of the kits with universal components. Typically, only relatively inexpensive mounting brackets and other related components separate, say, a 2006 GTO kit from a 2002 Camaro Z28 system.
The Roots/screw-type systems generally require a dedicated intake manifold that must be matched to the heads, and casting an entire intake manifold is a lot more expensive than laser cutting a steel mounting bracket for a centrifugal blower.
Where Roots/screw blowers can narrow the price gap with centrifugal kits is in the installation labor charge. Typically, it takes less time to install a Roots/screw-type system on most vehicles, as centrifugal blowers typically require more extensive modification of the accessory drive system.
The relative ease of installation and tuning, as well as the limited impact on other factory vehicle systems, makes a bolt-on supercharger an increasingly cost-effective alternative to a custom-built engine. That’s exactly what Berger Chevrolet did with the latest versions of its limited-production Berger Camaros. On its earlier fourth-generation models, the dealership sourced custom, 500-hp, naturally aspirated engines that cost much more to build and install than the Magnuson kits used on its fifth-generation cars.
Here’s the 550-hp engine of the Berger Camaro. It uses nothing more than a Magnuson kit (non-TVS compressor) and the kit’s supplied tuning upgrade. It is a simple upgrade that delivers a huge increase in performance.
Positive-Displacement Versus Centrifugal Blowers
When it comes to supercharged horsepower, positive-displacement superchargers and centrifugal blowers produce it differently. In simple terms, a centrifugal supercharger’s boost increases exponentially with engine speed, while a positive-displacement supercharger’s airflow is linear with maximum boost occurring very low in the RPM band. That means a Roots or twin-screw blower that delivers, for example, 500 cfm of air at 2,500 rpm pushes 1,000 cfm at 5,000 rpm.
With a centrifugal supercharger, boost builds in a nonlinear way, much like a turbocharger. As RPM increases, the airflow from the compressor increases at a faster rate. Because of that, maximum boost is not achieved until the engine’s redline, or maximum RPM level.
The differences in airflow delivery create very different performance curves and driving experiences. In general terms, a positive-displacement supercharger has a flatter power curve with more low-RPM power. The centrifugal delivers a greater feeling of increasing power as the revs climb. On the street, and all other things being as equal as possible, a positive-displacement blower feels stronger on the low end, especially directly off idle. A Roots or twin-screw blower makes a small amount of boost whenever the engine is running. The centrifugal, on the other hand, “rolls” into its boost and is generally easier to launch, with a stronger feel through the mid- and upper-range RPM levels.
Unlike a Roots or twin-screw blower, which delivers maximum boost at relatively low RPM, a centrifugal (such as this ProCharger D1SC) increases its airflow with the RPM, much like a turbo. Maximum boost comes at the engine’s maximum RPM.
The nonlinear airflow delivery also makes the centrifugal supercharger better suited for drag racing, because the graduated boost application enables an easier launch, with greater power coming on as the RPM increases. Of course, with peak boost not occurring until redline, the blower’s effectiveness is not fully realized at lower RPM.
In general terms, a street vehicle with a positive-displacement blower feels the effects of the blower immediately and at all low-RPM levels, while a centrifugally blown car feels more like stock until around the 3,000-rpm level. There is also a more pronounced application of the power with a centrifugal blower, but not the “on/off” feeling of a turbocharger.
How Much “Blower” Do You Need?
Unless you are adapting a GMC 71-series-style Roots blower, which is offered in tremendous size increments for drag racing, there is a limit to the effectiveness of many bolt-on, underhood-type superchargers. If the supercharger (be it a positive displacement or centrifugal) can’t flow enough air to support the engine’s high-RPM requirements, horsepower falls off and the effectiveness of the supercharger is greatly diminished. Increasing the boost pressure increases the effectiveness to a certain degree, but in the end a supercharger with a larger compressor is the best way to optimize the blower’s performance across the RPM band.
The great airflow capability of LS engines and the larger displacements offered in production and aftermarket versions of the engine make sizing a supercharger particularly important, as the smaller-displacement superchargers that were common on a street car only a few years ago simply don’t flow enough to support later and larger-displacement LS combinations.
