If you saw THE LATEST EPISODE of MCM where MOOG fits a new Harrop supercharger to his Lotus Exige, you might wonder what the deal with these things are and why there are so many different-looking superchargers. There are centrifugal side-mount ones, 6/71 and 8/71s, Eaton-TVS, twin-screw... so what is great and what is junk?
Let's focus on the modern style of top-mount supercharger used by car makers like General Motors (Chevrolet, Holden, Cadillac, etc) and Lotus. Side-mount superchargers, old Roots-style blowers (like what you see from our mates at Roadkill, below), and the big PSI or screw-type blowers are also very popular but to not confuse this story I'll look at them another time.
Any supercharger is basically just an air pump, where regular old atmosphere is drawn in and then squashed by a pair of spinning rotors mounted inside the case, before being blasted into the engine at a boosted pressure.
But, because they need the engine to spin them old blowers sapped a lot of power from the motor, and the air they fed in was often hot, plus they tended to wear out quickly with street use. So what changed with these modern superchargers to make them rad-to-the-power-of-sick?
The Harrop TVS1320 supercharger MOOG is holding is what is known as a TVS unit, or a Twin-Vortice Supercharger. To put it simply, this means the two rotors inside the awesome Aussie-made housing he's carrying in the below pic are different to the rotors used in other positive-displacement superchargers.
Positive displacement refers to the fact the supercharger jams its boosted air directly into the motor as it is bolted right down on top of the intake ports - you have essentially increased the displacement of your motor with this "large chamber intake" as I once heard an old school engineer refer to the concept as.
Eaton, a ginormous engineering company who make all sorts of stuff like differential centres and what-not, came up with what they reckon is the most efficient, power-adding design for a supercharger and their design is different from the other concepts for two main reasons: their rotors use a four-lobe design, and they have various different "twists" on different models to improve how the rotors mesh and therefore compress the air.
Here are a couple of pics of older-style rotors on the right:
And below are the Eaton TVS style, which Harrop, Magnuson, and Edelbrock use in the aftermarket. They are claimed to be able to spin faster and produce less heat as the four lobes spread the load along the rotor shaft, which also makes them less likely to wear the rotor tips, and should provide snappy boost any time you tickle the throttle.
General Motors have used TVS superchargers on all their serious high-performance cars for over 10 years now, with their performance constantly being upgraded as development improves. The two basic modern GM superchargers you might have seen are the TVS1900 (1.9-litres of air per-rotation) on the 6.2-litre LSA engines, or the TVS2300 (2.3-litres of air per-rotation) on the big-banger 650hp LS9 V8. The 755hp C7 ZR1 used a huge 2.65-litre TVS supercharger!
These factory superchargers use the same Eaton TVS rotor design, but have in-built water-to-air intercooler cores to cool the compressed air before it gets fed into the hi-po LS donks. This has been a massive improvement in supercharger reliability and performance, as it drastically reduces the risk of engine-killing detonation.
While turbochargers give massive power outputs sometimes how that power is delivered is more important, and the reason OE-manufacturers have been opting to supercharge their hi-po V8 engines comes down to compact packaging, great reliablity, excellent power-adding, and fantastic, linear power. With the TVS supercharger there is always power under your foot and it is faster-acting than most turbocharged engines.
In a street or circuit car application this is absolutely paramount, and this is why MOOG opted for an Aussie-made Harrop supercharger for his Lotus!