Noob to this forum. To share some thoughts after reading through this thread...
Without physics on solid vs hollow bars: The active part of the torsion is in the outer diameter of the bar. So do not be frightened of "hollow" as though it is somehow bogus.
No one (I think) has mentioned any attempt to verify coil spring rates. Yes, the "shops" have fixtures with dial readouts to verify ratings. If memory serves this reading is taken after some compression and then the rate read to compress 1" further. Below I will relate a diy setup which worked for me.
The bar lever arm is indeed important so the more progressive units may have adjustments in form of holes so that the active lever length may be adjusted. The look of some of the front bars here may not allow that. Some (race) bar arms may allow a collar to slide and be clamped.
No one (here anyway?) has played with the "torsion" bar type set up. These are very pretty, but likely require some bracket welding,and the bar portion is straight. To look at these use search "universal sway bar" and you will see circle track, hot rod, and rock climber sites or vendors. These bars are typically splined ends which take steel or aluminum arms and use rubber bush or heim joints. Some starter kits are as low as $100 (add fab/labor).
Here I will relate an experience I had buying an ebay spring set promising 200 lb/inch value (for another car). I had rigged up a crude measurement set up which I will describe below. The ebay set which promised 200 lb/inch measured 80!!! That value was less than the ones I wanted to replace. Returned and no response from the vendor.
I set the spring on a hydraulic press ( Harbor Frieight) . Under the spring place a (lowly) bathroom scale. Use a carpenters tape with stop so that it can measure the deflection. I used this set up on the junk above and then on Eibach as a referee test. The Eibach were right on. I wish someone would try (even) a fish deliar spring reading on a loosened sway bar end so we could compare!
One final thought on spring rates and this sermon will end. If you are looking at adapting coil springs there are simple formulas on line which address number of coils, dia of coil ,AND WIRE DIAMETER. The caps are important. If you are looking for a major increase over your current spring you should expect a bigger diameter "wire." Hope some of this helps someone.
