The Suspension in the 2nd gen RX-7's is pretty good. But this car is now over 10 years old and things do wear out.
And besides, you can never have enough grip in the corners :)
Before you start changing everything you need to sit down and figure out what the main purpose of the car is. Street only?, Track only?, or Some of both?. And you have to decide whether you can put up with the harshness of the track setup while on the street (rattling your teeth out). or give up some handling gains by going to a more comfortable setup. And of course how much $$ you want to spend.
a good link with install notes: Steve Cappelli's suspension install notes
Basicly to sum up this section. Any Flex and body roll / lean is the enemy !! :)
Chances are these will be shot if they are still factory ones.
And if you have the Auto suspension you will be lucky if it still works.
There are many choices for shocks, and a huge price range. For *normal* street
driving you don't need anything special. New ones from a local parts store
will probably do you fine if using the stock springs. For the rest
of you like to push to the limits. I would recommend some adjustable ones.
The KYB AGX are the best for the money. You can pick up the set of 4 for $350-400
if you look around. The next step up would be the Tokico Illuminas. Which
I think run $500--$600 for the set. Both these shocks are used with either
stock or "stock replacement" springs. By replacing these your auto
system will no longer work. But just disconnect the system and enjoy these
which are better anyway.
You can get much better / more expensive ones but they would be recommended for coil overs, which I'll talk about later on.
The best deal I can find is the KYBs at www.k2rd.com
Springs (stock size replacement)
After your car's weight has been sitting on your stock spring for so long. They are going to be sagging on you. Chances are your car is 1/2'"-1" lower then when it was brand new. Adding "performance lowering 'stock replacement' springs" is probably the most common suspension mod to a car. The lower car will give a better feel and the stiffer springs will reduce body roll (or lean) giving you more of a "on rails" feeling. There are many companies that make springs for this car. Racing beat (RB), Eibach, and Suspension Technique (ST) would be the 3 most common. All of them will give slightly different rides. The Eibach will be the softest, most comfort one. This spring is progressive so the more it compresses the stiffer it gets. Hitting a pothole while driving down the road wouldn't be much harder then stock. But get into a turn and the stiffer section of the spring will start to work. The ST ones are the stiffest and are linear springs. Which means as the spring compresses it gets constantly stiffer. Lots of people prefer this as they can better tell how the car will react, instead of the spring getting harder as you turn. But of course you are losing some comfort to gain this. I think the RB ones are in the middle. I believe all these lower between 0.75"-1" from *new* stock height. But as I mentioned before you car is probably sagging some. Some people have even had the car sit higher after adding new lowering springs. So the amount of lowering will differ from car to car.
Coil overs are the ultimate shock and spring set up. Coil overs allow you to change the height of the car by moving the spring perch (holder) up and down. Also in most cases you can pick the spring rate (stiffness) of springs you want to use. And you can change between springs (different rates for different tracks etc.) with out too much trouble or money. The cheapest (but still very good) are the Ground control kits. For $400 you get a kit that includes Eibach ERS 2.5" race springs (what basically every race car uses, Indy, F1, etc.) in any rate you want. And you get the adjustable perch and a new metal top hat. This kit is added to any "stock" shock as listed above. So you can match this kit to $400 KYBs and you have a coilover kit for about $800. All other sets I've seen are a spring and shock combo. Mazdacomp has a Koni race shock coilover kit that comes with camber caster plates, rear camber link, and Eibach sway bars (all these will be talked about later) for $1730, which I think is a good deal. Another company that makes them for our cars is Mazdaspeed. But I don't think they are worth the money. The next step is custom made ones. Such as shock tek, Which can get expensive.
The other advantage of coil overs is you are able to corner weight (or balance) the car. You put all 4 wheels on scales. And you can raise and lower each corner to adjust the weight balance across the car. There is a good info on it Here.
Left: Ground control kit. Right: Mazdaspeed coilovers
Strut tower bars help tie all your suspension together. They prevent your car body from flexing inwards under load, and give the car a much stiffer feeling. You can get front and rear bars. As well as a lower one that ties your front control arm together. There are many companies that make the front ones, but I've only seen two rear and lower ones. They are Cusco and Mazdaspeed. The Cusco bars are very nice. I'd recommend them for both the front and back at around $150 each. The lower cusco looks nice but the mazdaspeed one just looks stronger. The cusco one only uses one bolt on each side, where as the Mazdapeed uses both and hugs the control arm bushings. I've heard of no problems with the cusco though. The Mazdaspeed lower is about $135. Cusco is $105
You can get the Cusco's at www.rx7.com and the Cusco's and Mazdaspeeds at www.corksport.com
Mazdaspeed lower 
Cusco front 
Sway bars are underneath the car and help prevent body roll. basically the middle is attached to the body of car. And each end is attached to the control arm where the wheel is. What happens is when one wheel tries to move up (for example the left moving up as it compresses in a left hand turn). this bar tries to force the other side up with it. Since that can't happen it instead just keeps the left one down. This keeps the car flatter "on rails" through the corners. So the bigger the bar the less the lean. Sway bars can also effect your front to rear balance. By added a bigger rear bar to your current setup, it will help get rid of understeer. Or a bigger front will get rid of oversteer. Of course if you change it to much, not only will you get rid of over/under steer, but you will just create the other. As the same as springs the most common 3 brands are Racing Beat (RB), Eibach, and Suspension Technique. All come with new frame mounts with bushings, and use your stock endlinks. They run between $200 and $350 or so for the pair front and rear.
Rb sway bars 
You can also add new endlinks to your stock sway bars or to aftermarket ones. This will help as the 86-88 ones are rubber and will flex. The 89-91 are plastic which is better, but will still flex more then metal. Both RB and Mazdatrix make metal endlinks. They are also adjustable so you can set them so there is no load on the bar while the car is still. These run about $60 a pair, you need one pair for the front, and a pair for rear.
RB endlinks 
All the Suspension components under the car are attached to the body with rubber bushings. Even when new they would flex. (More comfort) but once again these cars are getting old. The rubber is probably wearing and flexing more then new stock ones. You could replace with new stock ones. But We'll go one stop farther and put in stiffer then stock ones. The suspension bushings on the 2nd gen would include the front and rear control arm, the front and rear sway bar frame bushings, and The DTSS rear toe steer bushings. While you are down there you could also replace the rubber engine mounts, tranny mounts, diff mounts, and subframe mounts. This is one of those mods were the parts aren't too much (well not each.. But they add up..). but the labor will kill you. Expect a couple full days of work to change them all. I haven't changed mine *yet* (this spring) but Everyone's always has good things to say after changing them.
There are 2 types of bushings to choose from. One is urethane, which is a stronger rubber and is about 40% stiffer then stock. The other kind is delrin which is a hard plastic which is basically solid. The delrin is a full race car bushing. Since they don't last too long. Probably only around 1 year of street driving. So unless your car is a track only car with a trailer, I'd go for urethane for the ones that move like the control arm. Mazdacomp carries them all.
The front and rear control arm bushings will give a much better feel while cornering. Well worth the $50 if you can stand the labor. The front ($40) is not that hard. But the rear($10) is! You have to drop the rear subframe down to remove the rear control arm.
Mazdacomp front control arm (made by energy suspension) 
The sway bar bushings will also help. If you got aftermarket sway bars they come with them. If not you can order the bushings for the stock bars. $25 for both front and rear.
The DTSS rear steer bushings ($60) are probably the most important to get rid of. This has been called a failed system by many. And that was when the bushing is brand new. It's probably even worse now if yours is worn out. There is a good write up Here about them.
Mazdacomp delrin DTSS bushings 
The other mounts consist of the engine (2), tranny, and diff (3). as well as the subframe (2).
Replacing the engine, tranny, and front diff mount will give much better throttle response as most flex will be gone. Also the single front diff mount (other 2 are "rear") is a common breaking point from doing burnouts and hard shifting. If you have a metal clunk in the back every time you let off and on the gas it's probably the front diff mount. I doubt you will notice any difference from the rear diff mounts and subframe bushings. Those are also a big job to do. I'm not planing on changing those.
The last rubber bushing is the strut tops. The only way to change these is with coil overs since they come with metal tops.
The last stage after getting all your new parts one is to get an alignment. You need to take your car to a local shop with the equipment to do it.
In stock form there really isn't much you can change. You can change the front and rear "Toe". Which is the angle of the tires as looking from the top. So either the fronts of the tires are closer together then the rear of the tires / \ (toe in), or Vs versa \ / (toe out). This is usually around 0. or a tad (like 1/16") in or out. This setting is really a driver feeling thing. So there is no "best" setting.
What we need to do (especially after lowering) is to be able to change the camber. Which is the angle looking from the front or rear. So if the tops of the tires are closer then the bottom / \ you get neg camber. And \ / would be pos. camber. Basically the more neg camber you add, the better the grip but the more wear on the tires. Stock is around -0.5 in the front and rear. Racers will run up to -4 or so. You can add a little bit more to the front of a stock setup as seen Here. But that's not much. What you really need is some front Camber plates, and a rear camber link if you want an agressive alignment.. The front camber plates will only work with coil overs. They come with the Mazda comp coil over kit listed above. Or you can add them to the ground control (GC) kit for another $300 or so. But with the GC kit you are required to machine down the shocks to make them fit. GC does this for you if you buy shocks from. I don't think it's that hard. I'll know this spring when I figure out how to do mine.
Ground Control Camber/caster plate 
To change the camber in the rear you need a camber link. It replaces the solid sublink that goes between the rear diff and subframe with an adjustable one. When you change the length of it the rear camber changes. These run between $80 and $110. Once again from mazdacomp and RB.
Mazda comp rear link 
Now about the worst thing you can do is spend all the time and money on the above, and use a cheap set of tires. It makes it all pointless. You want a good sticky summer tire on the road. Or even a R compound tire for the street. I saw alot of people running Yokohama A032R race tires on the street last summer and I'm thinking about running them myself. But expect them to only last 6 months or so. Also running a wider tire will help. but you can't get much wider on stock rims. 225 50's on the stock 16x7 turbo rims is pushing it, and it might rub a bit on the front. By getting wider rims you can run wider tires. like a 245 in the rear. you aren't going to get wider then 225 in the front without sticking outside the fenders or rubing. Also moving up to a 17" means you have a lower profile tire. which means less tire flex under load.
A032R's
* I am not in anyway connected with the companys listed above, order and send money at your own risk.
**all prices are correct as of 12/01
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