Taken from the 1970 AMA Specification. For reference use only. See Dealer Price Schedule for model application. Use this with the Spring Calculators on the project page to figure out what springs the factory installed on Nova.
Ride Height Issues
as example here are the specs for the HQ Spring:
Cut off length = 122.78
Wire Diameter = .628
Total Coils = 9
Rate = 345
Height Uninstalled = 16.45"
Installed Height @ 1830 lbs = 11.09"
All springs were designed to be 11.09" when installed. The "computer selected" spring first used in 1969 was fine tuned to the weight of the car with all the particular options.
There were 9 springs with the 345 rate. The differences are the wire diameter and the coil count needed to put the spring at 11.09" when the car was fully assembled with all options.
The shortest free height for the 345 rate springs was 14.97" and the tallest was 16.95". This is one of the reasons folks have a hard time with the generic 345 springs and body ride height. All 345 rated springs will do the job. The difference is the ride height you get.
Within reason, you could trim the generic springs to shorten the cut off length and lower the ride height. Alternatively you can install another higher or lower code to get a higher or lower ride height. My spring calculators use the parts book weights to specify the spring required to hit the factory ride height for that weight.
The springs sold by Chevrolet part number came on the scene several years ago to address the ride height problems found with the one size fits all generics. I do not recall who the manufacturer is for them. I doubt the retailers have the specs unless they measure them. They buy them based on part number or application.
Custom spring companies will sell you an equivalent spring to meet the ride height you specify. They would not be able to always match the wire diameter and coil count that came on the car originally. However the spring should function fine with the correct ride height.
If you want the stock ride height in your Nova, you need to know the weight of all the options. Then use the calculator to find the Chevrolet code. Then find the Chevrolet part number for that code. Then order the reproduction spring by that number. This will get you closer than just using a generic 345 spring. Note this does not guarantee the perfect ride height. You might still experience ride height differences. Just make sure you let the Nova rest on the springs long enough settle in before you take ride height measurements listed in the Assembly Manual.