I have been doing spring modifcations for years for myself and for other people...............details at my shop forum.
And for the record, I also do a quality aftermarket spring nstallation for people who buy them, so I know both sides.

I do some precise measuring before I do anything with stock springs.
I seem to be the only one on TR who can do the measuring right, and most people who are negative on cut springs probably should have brought their car to me before they messed it up.
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My car for years sits 3" lower on cut springs without blown shocks, without beaten up suspension and without eaten tires........I have photographic proof and........The car has been seen by hundreds of people at the meets I go to.
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It is not the "cutting" of a spring that will mess up a car. What messes up a car is a spring that is TOO SHORT......and a person can spend $300 for a spring that is too short and have the same problems as if they messed it up by themselves.

I don't do heating of springs to lower a car, as I have never seen it done
well, and don't know anyone who does it well.
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If you want to talk suspensions sometime, catch me at the meets I go to
or if you want to do a demo ride with me, you can see that what I say is true.-Bob

Ohhh...
For the record, every shock is a coilover shock if the coil is over/around the shock.........adjustable coilovers allow you to change ride height
for looks or your personal driving style.