Cutting/ Heating springs to lower a car are the worst possible things you could do, unless you have a fine tuned knowledge of how it will work (99% of the time it'll suck) then don't even touch it, but if you ever decide to ghetto-lower cutting is the better, although still a stupid choice. if you heat springs it will continualy lower the spring rate, which will over time lower the car more and more since you've weakened it's original integrity.
