The engine compression remained the same; the piston strokes upward to compress the contents of the chamber to a fraction of the "bottomed out" position of the piston; that change in volume is what Compression Ratio refers to. The supercharger "packs" or increases the volume of the air/gas mixture so when it fires, there is more explosive force which pushes the piston harder. This gives you more power than you would otherwise get.
Superchargers are not simple things to work with and normally require a different fuel pump, carbureator and other engine components. If the block casting is weak in the combustion chamber area, the added explosive force can literally blow a hole in the block or throw a rod! Trying it on the HJ long-stroke 4 invites disaster and possible injury because that engine is NOT designed for such an application.
Jack Mueller
Resident Engineer, Nemak S.A.
General Motors Powertrain Engine Plant-Gen V engine program
Tonawanda NY
