727pilot That is the spring rate per inch of travel. 350 pound load to compress the spring 1". You want the car to squat to put added load on the rear tires for traction. If the rear is squatting too much adjust the dampeners on the rear shocks. 350 is a good place to start for a street car. The only thing you didn't say was what is the angle of the shock in the car from mount to mount. The more angle on the shock and spring, the more dampening you need. Video the car squatting, the rearend should drop about 1-1.5" total. Thats a good start. Are the tires rubbing the inner fender wells? Have you had the car weighted at all 4 corners? Wheel alignment? Find a dirttrack guy with scales and get the car balanced with your weight in the drivers seat. Next get the car aligned with a thrust angle of 0 degrees. After this is done see what you have. Does your car have 2 or 4 shocks in the rearend? Answer these questions and we will give you the best direction to go. You have to remember that a street setup is alot softer than a race track setup. about a 35-40% increase in spring rate alone.
This will also make the car ride like a truck on the street.
Fill in the questions. Angle on the shocks is IMPORTANT also Rick Lake