Supercharging
How it works:
Like turbocharging, supercharging is a means of forced induction that pumps greater amounts of air into the combustion chambers than atmospheric pressure would normally allow. When mixed with the right amount of fuel, the denser air creates a more powerful burn at combustion, which pushes harder on the pistons, therefore increasing power.
A supercharger is different from a turbocharger in that it's driven by a direct mechanical link to the engine, often a belt that's turned by the crankshaft. This is also a good-news/ bad-news scenario. The good: There's no wait for exhaust gas pressure to build in order to deliver boost; the surge starts right off idle and power delivery is linear, rising with the engine's speed. The bad: A certain amount of the engine's power is required to turn the supercharger, in a state called parasitic loss.
Superchargers fall into two main types: Roots-style (known as screw or positive displacement) and centrifugal (known as dynamic). The Roots-style blower typically consists of a case, located between the intake and the cylinder heads, that houses two large screws, or rotors. These screws are driven by the belt off the crankshaft, and their spinning action compresses intake air, sending the dense charge to the cylinder heads.
A centrifugal supercharger looks and acts more like the compressor side of a turbocharger. It's also driven by the crankshaft, either via a pulley or gear set. But centrifugal blowers also contain a gear-drive system inside the case that can be set to drive the compressor wheel faster than the engine's speed. Some centrifugal superchargers can be equipped with a compressor bypass valve that bleeds off air pressure during deceleration (much like a turbo's blowoff valve) to reduce heat build-up and eliminate compressor surge. Centrifugal superchargers are smaller than Roots-style blowers, making it easier to find room for one in an otherwise crowded engine compartment.
Where it works best:
Street, drag racing, road course
Bang for the Buck rating:
"Superchargers aren't cheap. However, the power made by bolting on a Stillen supercharger package is reliable, repeatable and FUN!"
- Michael Ullrich, Stillen
Dope:
"There is an old saying that when it comes to cars, with the choice of power, reliability and affordability - you can only pick two. This is true for turbochargers, nitrous and all-motor vehicles. But a well-engineered supercharger can give you all three."
- Michael Ullrich, Stillen
"The basic difference [between a Roots-style and centrifugal supercharger] is with the power curve. The Roots-type is rather steep under 3,500 rpm, then crosses over the centrifugal curve and flattens out. On the other hand, the centrifugal curve is linear in nature and delivers power much like a rheostat does. The power continues building to and beyond the engine's redline. With high-revving sport-compact applications, power delivery of the centrifugal is preferred over the Roots-type."
- Vortech spokesman
"The Roots-style supercharger has instantaneous power delivery and will build a broad, flat torque curve. The focus is on useable power, not peak numbers."
- Michael Ullrich, Stillen
"There is no bottle to fill, no exhaust manifolds to install, no seeking out that neighborhood garage for a 'funny' smog certificate every two years. We've had owners report up to 150,000 miles on their original compressor!"
- Vortech spokesman
"Oscar Jackson is getting back into the game with a new supercharger setup. He's using the Rotrex supercharger, which spins a lot faster than the traditional Paxton or Roots-style that they had, to match the higher engine speeds people are turning now. I think that's going to put it back on the map."
- Tony Shagday, Skunk2 Racing
Nope:
"Because superchargers deliver boost via rpm, the shock on an engine's internals is dramatic. You're slamming forced air directly on those components, and they're getting pounded."
- Tyler Tanaka, Turbonetics
"With a centrifugal supercharger, you get a lot of the negative aspects of a turbo and fewer of the positive aspects of a supercharger. A centrifugal supercharger is like half a turbo (on the cold side) with a belt strapped to it. These generally produce peak-type power - generally limited to upper-mid range and top end. Plus, installation can be a nightmare with complicated tubing routed from the intake to the unit, from the unit to the intercooler (if one is available) and finally to the intake. There is also the constant restriction of the unit itself at low rpm as well as the constant drain on the engine, due to the crank-driven belt."
- Michael Ullrich, Stillen
By Brian Gillespie
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