The stock ride height of any car leaves a little to be desired in my opinion. I am not a big fan of showing off my inner fender wells. This was one of the first customizations I did to my car due to the fact that it was very simple and very cheap. I bought the Grab-a-Trak 620 front coil springs on eBay for $59, which was slightly less than ordering directly through Mustangs Plus.
These are really nice springs as they come black powder coated, so they retain a nice finish (mine still look new after 3+ years of use). See Fig 1 for a comparison between my stock springs and the 620s. I went ahead and installed them stock since they were supposed to provide a 1" drop compared to the stock springs. I bought an internal style spring compressor because I knew I would be taking these off again someday for a disc conversion — it turns out I have probably taken the springs off 4 or 5 times. You can get a good spring compressor at Northern Tools for around $30.
On a Mustang you will run into an issue with the large screw in the coil spring compressor being too long to allow for proper compression of the spring to get it out of the car. The spring will drill right down into the spring perch long before it is compressed enough. My solution was to stock up on heavy duty washers at the hardware store instead of cutting the shaft of the tool (see Fig 2). Additionally, when installing the new 620s with the powder coating you may want to take an old bicycle tire tube and cut four short strips to place over the arms of the spring compressor to protect the surface of the coil.
Now for the post-installation reports... As you can see from Fig 3 the initial installation didn't go as planned — I wanted a lowered Mustang, not an off-road Mustang! I removed the coils and called Mustangs Plus immediately. It turns out they had sent me the wrong springs on accident — the ones I had were for a big block 67-70, so they were much stiffer than the 620s. They offered to send me the correct ones, but after discussion we decided that for the ride height I wanted I would have to cut the 620s as well. I decided to keep the ones I had and cut them with a hacksaw. It was a lot of work and a few blades to make it through the thick coils, but it could be done in my garage.
It is generally recommended to cut 1/4 of a coil at a time. Based on the ridiculous height of my car and from what I read I decided to start with 1 full coil (see Fig 4). Luckily the full coil wasn't too much, and it put the car at a ride height that I liked (see Fig 5). After cutting off a full coil there is very little compression required to install the spring into the uncompressed suspension, which makes removal and installation a snap for future upgrades.
Two other things of note: many people suggest that springs will settle as much as 1" after driving the car a bit — I have had mine on for over 3 years and have noticed no settling. Also, there is a misconception among some that the 1" Shelby drop will lower the car. I did the Shelby drop after I installed and cut these springs and didn't see any noticeable change in ride height.
