Scott,
I have an Excel spreadsheet from Katz that you can use to figure out some spring rates.
However, to use it, you need to know everything: vehicle weight, front/rear bias, spring angles, motion ratios, wheel travel, lateral G loadings, etc. etc.
On II Much, with a vehicle weight of 3100 lbs (est.), 48/52 f/r bias (also est.), nearly upright springs, motion ratios of .7 in front and 1.0 in the back, it recommends a 475 lb spring in front and 225 in the back for a street setting. For a race setting those become 550/250.
Those design parameters are with 2 inches of bump and 2 inches of rebound travel and allow 1.0G on the street setting and 1.15G on the track settings.
I'm happy to send it to you if you want to play around with it. Katz does good work.
jp
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