Inside the LS9's supercharger and the newer Magnuson TVS units is a new four-lobe rotor arrangement that's a big improvement over the previous three-lobe design. Where the twist of the rotors on the older Gen V units was 60 degrees, the new TVS rotors are at an aggressive 160 degrees. Also, the lobes' intermeshing design helps quiet the supercharger, even at high rpm. In fact, the new Gen VI four-lobe blower design provides up to 10 dBa less case-radiated noise than the Gen V blower. The rotors are coated, and when spun up the first time they "self-machine" for extra tight tolerances.
The Roots-type blower has been around a long time, nearly 150 years, and was patented in 1860 by Philander and Francis Roots. The brothers didn't have any Chevys to bolt their invention to, so they used them to ventilate blast furnaces, coal mines, and other places that needed air pumped in. The Roots isn't a compressor, but rather a blower. Air compression doesn't happen inside the supercharger. Instead, it occurs between it and the intake valves. The Roots unit blows more air into the intake than the engine can flow out, so that air compresses.
Nothing makes a bolder statement than a 6-71 or 8-71 blower bolted to the top of a Chevy mill. Even though they've been around for a long time, these Roots-type superchargers continue to be refined and enhanced. Weiand claims to have improved the boost on its units by 14 percent. Its two-lobe rotor design features forged rotor shafts, and Weiand has completely revised its case design and beefed up the front bearing plate for more strength. These work amazingly well on stroked and smaller-displacement mills.
In a twin-screw-type supercharger, compression happens inside the blower. Air is pulled through a pair of intermeshing screws designed much like worm gears. The intake is positioned on the end of the two screws, which are designed to overlap, but not touch, leaving a small gap or pocket. As the screws turn, the gap gets smaller. This compresses the air as it moves along the screws up to the point where it enters the intake. Due to the lower charge temperatures of screw superchargers, they can easily run without an intercooler in lower boost applications.
A centrifugal-type supercharger operates nearly identically to a turbocharger. The main difference is that expelled exhaust gases drive a turbo via a turbine, while a centrifugal supercharger is driven from the crankshaft by a belt or gear. As with any centrifugal pump, the boost created by the supercharger increases with the square of the rpm. That's why this type of supercharger creates very little boost at low engine speeds. In the past there's also been a problem with this type of supercharger making too much boost in the upper ranges in addition to too little down low. Balancing top end and low-speed boost has been improved over the years through better impeller design and unit sizing. The centrifugal design is considered by many to be the most efficient even if it loses out in its ability to produce boost at any rpm like the Roots or twin-screw superchargers. Given its lack of low-rpm boost, it's a popular bolt-on for cars that have engines big enough to provide good off-the-line acceleration without it. If it's bolted onto a smog-regulated later-model car, it's also pretty easy to remove for annual inspections compared to a turbo-not that we would ever condone such a thing.
Today supercharges are more popular than ever, and there's a huge array of bolt-on kits to choose from. Even with gas prices rising fast, they're the hot ticket since they offer the best of both worlds: more power and improved mileage.