Miata Bilsteins

Alright I know that by using NB/Fat Cat top mounts I can then use Bilstein shocks made for the NB miatae. If I keep the oe NA springs and use NB shocks and top mounts, the car will be lowered appx. 1/2 inch. All of these previous statements are well understood by me, what is not is whether to use the HD or sport version of the shocks. I tried asking this question on a big miata forum and the only person that made an actual response obviously failed reading comprehension. On the fat cat site the only version of the shock that is discussed is the hd version, the sports are slightly more aggressive in their valving and have a shorter body to be used with lowering springs, by my logic the car will be lowered a little and with the fat cat bumpstops adding to the spring rate a more aggressive shock would be a good thing. Am I way out in left field or something?

If you are intending on keeping the setup you described, the sport dampers wouldnt be nesessary, but I dont think they would hurt anything. If you intend on lowering the car by using shorter springs, or increasing the spring rate, then the sport would be preferable over the HD. If you are going to stick with stock springs, the HD would probably be better. I know nothing about miatas, but that is the case with the Volkswagen bilstiens i have had experieince with.

A couple of things... check with Fat Cat, but it looked like the mounting hardware they give you is directly compatible with NA shocks, but not NB's.

Also, if you are running shocks for the NB, you will need springs appropriate to the NB as well. The lower perch and spring bottom is different, so you need to maintain the two, or get a threaded sleeve.

Also, what springs are you running? It sounds like stock ones. You do not need to go with the sport shocks to account for the lower height. The springs are just as long and maintain the same travel distance (NB mounts raise the upper perch... so the car is lower but travel is the same).

The FCM bumpstops won't increase your spring rate either. They will only come into effect when you're at the very end of your suspension travel, which won't be often on stock springs.

Therefore, you really don't gain anything by going with the sport shocks, unless you're planning to upgrade to beefier springs later. In fact, HDs will be a better pair with stock springs. The valving on the Sports will be too much. (Even the valving on the HDs is going to be a bit heavy.)

Make it easy on yourself and call Shaikh at Fat Cat. He can walk you through the thousands of options available, but the short version is this- there are many combinations of springs and shocks will "work", but what works best will depend on your car and your intended application. The beauty of using Bilsteins (either HDs or Sports) is that they can be revalved for a pretty reasonable sum as your needs and available budget changes.

Shaikh is at Solo Nationals this week (I just talked with him today, he's hunting for a trophy in E Stock) but he should be back at the shop early next week.

A couple of things:

There's nothing magical about the Bilsteins that lets you use them in an NA with NB mounts or whatever. If you can use the Bilsteins, you can use any other Miata shock in that application.

If you keep the generations together, you can install the complete setup in any model year. In other words, NB upper mounts, NB springs and NB shocks will bolt right into an NA without any special bushings or adapters and they will sit at their design height for the NB (or slightly higher due to the lighter weight of the NA). There's a problem with installing NA front shocks in an NB, but I don't think anyone cares unless you're simply trying to get a race 2004 Miata on to the dyno while its shocks are off being rebuilt...

I think Brad has this figured, that's more for the peanut gallery.

Can't really comment on HD vs Sport Bilstein, sorry. I don't have the direct experience. That's Shaikh's area of obsession.

Good luck at Nats, Tom! Say hi to Shaikh for me too.

Which one of the two is valved like the R-package cars? Those are quite stiff for a street car, but not bad for a stock track/autox car. IE, if this is a street car, go with the softer option.