Among both adjustable and nonadjustable shocks, there are basically two different designs: the mono-tube and twin-tube. The twin-tubes are also the standard low-pressure hydraulic dampers. Mono-tube shocks employ high-pressure gas as an additional effort to minimize the creation of bubbles in the hydraulic oil that occur any time oil is pushed through an orifice. Using high-pressure nitrogen gas in a sealed container, like a bag, limits the creation of bubbles in the oil. This helps shock performance especially in handling situations where they are subjected to serious abuse. The twin-tube, low-pressure shocks still work well, but generally the high-pressure shocks offer a slight advantage. Koni for example, sells both styles of shocks, as does Tokico and Edelbrock. This gives you a choice in terms of performance versus price.
Specialty ShocksWhile nonadjustable stock replacement shocks do an adequate job of improving handling over worn-out original shocks, when it comes to high-performance applications, stock shocks are often found wanting. Starting with drag racing, this situation actually requires shocks for the front and rear that are often much softer than stock. For a typical street/strip car, you're looking for front shocks that allow easier front-end travel to establish a given rate of front-end rise to help weight transfer to the rear tires. Competition Engineering, Koni, QA1, and others offer adjustable low-pressure twin-tube shocks that can be fine-tuned to work with your particular requirements, which can actually change from track-to-track. This is why adjustability is so important.
Rear shocks are also important in this traction equation, and also offer a slightly longer extension to prevent bottoming out the shock when planting the tires, especially with suspensions with an excess of 100 percent antisquat when there is separation between the tire and the body at launch. The last thing you want is for the rear shock to bottom out, which will cause instantaneous tire spin. These shocks are usually single-adjustables, although you can invest in specialty coilovers that are double-adjustable.
Drag-racing shocks are also referred to in a slightly different way than most other shocks. Often you will read references to rear shocks that are 50/50 or front shocks that are 90/10. Basically, these are references to the amount of force applied by the shock to resist movement. In the case of a 50/50 shock, the resistance is the same in both compression and rebound, while a 90/10 shock has nine times the resistance to compression than it does to rebound. The 90/10 is almost exclusively a front shock designed to extend (rebound) very easily and offer significant resistance to compression. This allows the front end of the car to rise very quickly and easily and then maintain that front-end rise throughout the entire run.
Better handling on your favorite twisty primary highway calls for a whole different set of shock requirements. Generally, this can start with a shock absorber that is shorter in length because the vehicle has been lowered, but also because the amount of suspension travel is greatly reduced. These shocks are almost the opposite of the drag shocks, since rebound damping is greatly increased given the increased spring rates that road-race-style cars generally employ. This is another area where adjustable shocks are an excellent investment. The key is to first choose a front and rear spring rate that works, and then begin tuning the ultimate handling and the relationship of the front to the rear with the shocks.