The motor itself was initially designed for turbocharging and is essentially the same motor as came in the AWD Mazda 323gtx which was an OEM turbo car. Most guys say you can achieve near-stock reliability up to 250whp... above that you start sacrificing longevity... although there are quite a few 280+whp stock motors out there with some decent mileage on them. The key (as in all FI applications) is the tune.
Going standalone in the Miata community recently made a huge leap with the introduction of PnP Megasquirt ECU's. For under $1000, you can purchase MS PnP, LC1, IAT sensor, vari-tps, and have a complete solution. The MS software is some of the best out there. It has been proven around here that you can do the entire rest of your turbo setup for under $2k ALL QUALITY PARTS that will take you as far as you want to go. Currently, MS PnP is only available for 90-95, but you can build your own for any year.
T25's of all sizes are good to about 250whp and are a more common turbo... most of the smaller-sized T3's will get you to the limits of a stock motor with more top-end and only a small amount of spool sacrifice over a T25. If going with a bigger T3, you're sacrificing a lot of spool time for the top end... good for racing, bad for street.
Most people will reccomend that you look at 94-95 cars. Starting in 1994, you get a 1.8litre motor, additional chassis bracing, a larger rear dif w/optional Torsen, bigger brakes, and still stay OBD1 which makes tuning easier. The 90-93 cars use a 6" dif which can be blown on stock power... is a timebomb with forced induction especially if you're going to track it. However, the 94+dif/axles/driveshaft is a straight swap with previous years... a common upgrade. The 5-spd transmissions from any year are generally good to 300whp and the 6-spds out of later years are good past that. The larger brakes from the 94+ cars are a direct swap as long as you use the 94+brackets... very common upgrade. 94+brakes, braided lines, and decent pads should do fine for up-to-moderate track duty.
Some cars, there is no common trait, have cooling issues when going FI. A common upgrade for the system is to replace the stock radiator (plastic end-tanks fail around 100k miles) with an all metal radiator designed for an Automatic-trans Miata. Of course there are the big aluminum Koyos, but in most cases, they're overkill. An auto-rad, NACA duct, and WaterWetter are usually enough to calm any cooling problem.
Suspension options are endless, but popular choices are Ground Control CO's, Koni's, KYB AGX, Tien, and a few others. Swaybars, chassis stiffening, etc are mostly the usual stuff you'd find on any aftermarket list.
Roll bars come in many flavors, and roll cages are almost always custom jobs that need to conform to the specs of the governing body's rules for that particular racing. For most AutoX and HPDE, you only need a rollbar that is taller than a helmeted driver... but check.
Tires and wheels I won't touch on cause I don't know enough... but I've been stoked for a long time on my $90 15" Heliums and $75 T1R's... lasted me over 10k street miles so far and still a bunch to go.
V8 Swaps are getting more common as the prices of earlier Miatas goes down, but are still expensive and require a HUGE amount of work. Much easier to blow 15psi.
Overall, it might be a good idea if you got a car that was already modded in the way you're looking. The classifieds here are mostly turbo cars, but at miata.net, the classifieds are mostly mildly modified non-FI street cars.
Check this out:
At 200whp, decent rubber, and some shocks/springs... you can outrun anything FWD, and just about any stock car out there short of a Z06. It's gonna take some serious money for something like a Mustang or 350z to even stay on your tail.
There are some great reads to get you fully up to speed. If you're serious about this "miata" thing, then read through these links to get the full picture:
DIY FaQ - All your answers in one big post
2nd post in this thread:
Probably the most comprehensive website to get a good feel for the performance Miata aftermarket (excluding FI) is here:
You can compare pricing and do your homework.
I highly recommend you find a Miata Club in your local area, go to one of their monthly meetings/runs, and find the speed-freaks and get an education. BTW, please put your town in your PROFILE so locals on this forum can get in touch with you.
...and I'm spent.