I just wanted to inform some people about positive displacement superchargers.
There are several "Brands" out there.
Let me clear up some confusion about the compressor (The main part with the screws that has the displacement):
--Ford OEM on the Lightning, both 03/04 and 07 Cobras, and other cars except the Ford GT have an Eaton compressor.
--Ford Racing's 2V supercharger has an Eaton Compressor.
--Roush Superchargers (that I've seen) have Eaton Compressors.
--Saleen Series I and Series II have Eaton Compressors
--Allen Engineering Superchargers have Eaton Compressors.
--Ford GT's supercharger has a Compressor from Whipple
--Ford Racings Cobra upgrade has a Compressor from Whipple
--Saleen Series IV, V and VI all have Compressors from Whipple
--Makes aftermarket kits for most Modular Ford Engines.
The Eaton is referred to as a "Roots" supercharger and the most common compressors on ford engines are the M90 and the M112. Oddly enough, it's screws look much more like twins than the twin-screws.
This is where it gets tricky because they are all interconnected:
SRM liscensed twin screw compressors as early as 1951
SRM formed a sister company: Opcon Autorotor.
Opcon Autorotor parted ways with SRM.
SRM formed Lysholm.
Lysholm formed a partnership in the U.S. with Eaton.
Opcon bought Lysholm.
Kenne Bell uses Autorotor Compressors.
Autorotor is a subsidiary of OPCON, a swedish company.
OPCON bought out Lysholm in January of 2004.
Up until 2005, Whipple used Lysholm Compressors. Now, Whipple makes their own.
Kenne Bell and Whipple have been in competition with eachother since roughly 1991 however they both use a very similar design. Kenne Bell explains why it chose to use Autorotor compressors over Lysholm in the following article this page
There was a backlog of Whipple orders and rumors that the company may be going out of business. It turns out that Whipple has since moved away from lysholm compressors and now manufacturers their own units in-house.
Here is a great link from Whipple's site on the history of the twin-screw: History of the Twin Screw.
Regarding Lysholm's future:
"The demand for our products on the US aftermarket remains strong and a new sales organization will enable us to meet the increasing demand and further develop the existing potential in the US automotive and Marine aftermarket. We will further develop our distribution channels and our support for these products in the US," says Martin Stenbäck, CEO of Lysholm.
Autorotor/Whipple/Lysholm Twin Screw (I believe the 4/5 lobe design is more common than the 3/6 pictured below)
It's important to note "Twin Screw" superchargers tend to be more thermally efficient.
Here is a link to a good site with detailed info on how these superchargers work (as well as centrifugal SCs):
Allen Engineering Superchargers
Kenne Bell Superchargers
Whipple Superchargers (site was down when I wrote this)
Roush (Run a search for superchargers)