Threaded sleeve and perch kit options (AKA Coilovers)

I am upping my suspension rates again. My new setup will probably be too hard for my Bilsteins, but one day I'll be getting the revalved for even higher spring rates. An intergal part of my project is the ability to adjust ride height and use standardized spring sizes in my suspension. Threaded sleeve and perch is what I need.


Ground Control sleeve/perchs used to be the most popular kits. A lot of people don't know all the choices out there. Talk to any dirt oval guys and they'll tell you a lot of cheap, high quality options. If it is good for these guys you know it is good for us. I haven't bought any of these kits so I can't do a review on them, but I'd like to list these so we'll know that they exist. Oh, and also, coilover kit is much easier to type than threaded sleeve/perch kit, so I will just refer to them as coilover kits from now. 


1. Bilstein/Koni kits
Bilstein and Koni both make coilover kits for their shocks. Bilstein shocks for Miata are 50mm in diameter. Bilstein makes kites one for a smaller, 36 milimeter diameter shock and one that is 50mm. Bilstein coilover kit takes 2.5" springs. I believe the Koni sport shocks are 42mm in diameter. Koni makes a kit thats 42mm and 50mm.  You can probably use the 50mm Koni kit for the bilstein shocks. Bilstein kits are slightly cheaper so there is actually no reason to do that. Too bad Koni shocks for miata aren't 50mm? I think their RACE shocks are monotube and might be 50mm. If you have a set of these shocks please let me know what the diameter is and I will update this post. 


Part numbers for 50mm and 42mm kits
Bilstein: BSN-B4BOA0000117
Koni: 80-0000-1


2. AFCO Kit
AFCO has different series shocks. The ones we should be looking at are AFCO smooth-body shocks. I believe oval guys use these shocks a lot. Anyways, I have to apologize, I found out which series shocks are at the size closest to the Miata applications. If you do  some google research and find out, please let me know. AFCO makes threaded sleeves for all their smooth body shocks. The thing to do would be to get the sleeve thats very close but bigger than your shock body outer diameter, and make a sort of centering ring. Rubber o-rings, PVC pipe, etc are all options. These are cheaper than the Bilstein/Koni kits, and the sleeve material is steel. They sell each part of the kit seperately, so if you drive an NA you can probably save money by ordering just the sleeve, perch, and whatever else you need to secure the perch.


3. Mystery Ebay kit
If you go on any car forum, these kits are in hot debate right now. A lot of skepticism and optimism about them floating around. These are under 100 dollars and are by far the cheapest option. If you've noticed "economy" is a big theme in this blog. So guess which one I picked? I am going to make a seperate post goimg into detail behind the truth of these kits, so please check back!


3.5 Ebay-OBX kit
OBX, who have made sort of a brand name for themselves through their sales of decently priced medium qualify exhaust hardware and misc. parts, have started making coilever kits. As i will explain later, I can't imagine these kits being substantially higher quality than the other ones. 


Note on materials
All of these kits and the Ground Control kits are made from T6 series aluminum, with the exception of the sleeve part of the AFCO kits. They are all machined. I can't imagine any other way to make them.