I upgraded the stock Z28 springs which I think were around 350 lbs/in to Guldstrand autox springs 650 lbs/in. The springs were cut multiple times to get the right stance (trial and error). I drove the car several years until I upgraded again to Guldstrand race springs 900 lbs/in because I was still experiencing too much dive while autoxing. Again the springs were cut to get the right stance. No spacers. Because the springs were cut, the spring rate probably exceeds 1000 lbs/in. One would think that 1000 lbs/in would be too much, it isnt. My ride is still compliant and not jarring in my opinion. I also use ridetech adjustable shocks with custom valving to control the springs. Also my front end is light due to an aluminum 427 sbc.