In case you need more information: From the eternally usefull
ShawnB suspension thread:
SR20Forum Exclusive Springs To include Hypercoil (Hyperco) and Road Magnet springs.
Now you know the difference, here is the rest of the particulars on the SR20Forum Exclusive springs.
Hyperco Springs (Hypercoil) -
http://www.hypercoils.com/ (Applications: B13 and B14 only)
Hypercoil is a manufacturer that specializes in racing springs and custom springs for high end tuners (Hennessy, etc.) Some of the brighter suspension minds on the forum, including Chriscar and Choaderboy2, were trying to get a spring manufactured specifically for our B13 platform. A spring that could be used with an OEM length or shortened strut. A versatile spring comfortable enough for a (firm) daily driver, stiff enough to stay off the bumpstops, affording a slight drop (1" both front and back), and good for fairly serious auto-cross or road racing (not street racing, duh.) After much trial and tribulation the Hyperco Gen II spring was born. It is a brilliant design and execution, and is the brain child of the Hyperco Engineers and our very own forum brainiacs.
You want Hyperco Gen II's. The Hyperco Gen I's were...too low and too soft. Long story, they got redesigned. The Hyperco Gen I' s (purchased pre-owned) would work well with CSK's for a nice daily driver.
Hyperco Gen I Spring rate: 110-180 front, 75-174 rear, progressive rate
Drop: 1.40 front, 1.25" rear
Struts to use: CSK's only, no OEM length struts.
Price: Long discontinued.
Hyperco Gen II Spring rate: 110-290 front, 75-200 rear, progressive rate
Drop: 1" front and rear
Struts to use: AGX's or better yet CSK's.
Ballpark price per set: $330.00 new and they don't depreciate much. If you see them used and want a set, move damned quickly.