This is not the usual mod you found out here where being LOWER is the PRIMARY GOAL
This mod will allow your car to be lowered on spring/coilover while carrying heavy weight in the back (camping trip / towing a trailer / etc...)
Before this mod, I would always spin the rear perch up max manually when camping, that would take me a good 1/2 hour and sometimes would barely be enough to prevent the tire from rubbing.
After this mod, it would just be a matter of inflating the tubes to a higher PSI, I haven't tested the airlift 1000 with the trunk full but I can tell already that it will support more weight without rubbing tires.
So here are few reasons why you would be doing this with your lowered car:
1- You often carry heavy weight in the trunk
2- You tow a trailer
3- You raise your car every winter (with airlift you'll do the job in half the time)
4- Your suspension is saggy in the rear resulting in rubbing tires, Airlift should make it a little stiffer and prevent that
Let's get to work !
1: First thing is to contact the AIRLIFT manufacturer to find out what kit will work with your stance and coilover/springs. You'll have to tell them the inside diameter and height of the coil at ride height (installed as the car sits in the driveway; no additional cargo/passengers): http://www.airliftcompany.com/contact.php
I got Raceland coilovers, The inner diameter of the spring UNCOMPRESSED is 3.5in and the coil height with the car seating on a flat surface (not jacked) is 3.5in from the top of the perch (cut as shown in the picture below) to the rubber part at the top of the spring. I gave them those measurement and was told to get the Airlift 1000 kit 80754 which needs 5.5 inches in heigh in the compressed spring.
2: you purchased your kit, next we need to cut the perch to make enough room for the bag inside the compressed spring unless you don't use the perch at all of course (I had to try a few cuts to avoid affecting my stance, the less you cut the higher your car will be at the lowest PSI).
3: Now we need to insert the bag inside the spring, using your knee, compress the bag and slide in using a stick to force it inside, don't be shy here, you'll have push hard, here is the final result
4: Drill a hole above the spring to route the air line to the bags
5: Now connect the airlines to the bags and couplers, it's all explained in the manual and is very easy to do. You also have the option to run the lines separably using two air-valve (without coupler), doing so will isolate the bags resulting in more stable cornering, see comments posted down below for more info.
6: connect the air line to the inflation valve (choose your favorite spot, I liked this one for being hidden and easy to access). Airlift provide everything, you just need your tools
7: Test the setup by inflating it (lowest PSI while driving for my airlift kit is 5 and highest is 35, your kit might be different)
8: Protect the air line with plastic wire loom and zip ties
9: Enjoy (shown below is airlift @ 35psi)
and here is the car seating with 5 PSI
10: If the stance is is ****ed up at the lowest PSI, remove the lower red protector if the perch surface is flat (like the pic below, so it doesn't damage the bag), that way the bag will have more room inside the spring