Useful Notes & Information Pertaining to Common Upgrades or Repairs on the NC Miata / MX5
There's a lot of information floating around pertaining to the NC Miata and common upgrades and repairs, but very little of it is all captured in one spot. It exists either in community information repeated endlessly on facebook and can be hard to discern from the truth, or buried in various forum posts. In an effort to consolidate and vet the information out there, I'm going to start documenting my findings here.
Quicklinks:
NC Miata Coolant Expansion Tank
A known failure point on the NC Miata is the coolant expansion tank. These are plastic from the factory, and become old and brittle with time and temperature changes. These are pressurzied expansion tanks as well, and sure enough what does a brittle and cracked expansion tank do? Well it ruptures rapidly dumping a bunch of coolant out of your motor. This is a great way to have a catastrophic failure. This is a pretty simple fix, ranging from $75 for knock offs of the Moroso unit, $250 for the Moroso unit, and then some other fancy options can be bought beyond that if you so choose.
Morso also makes an aluminum power steering reservoir. This is also renowned for aging and becoming brittle, but as it is not pressurized it does not crack. Going aluminum though ensure sit's durability and also is claimed to provide some cooling improvements. Your mileage on that may vary however, and this is not considered as essential of an upgrade as the coolant expansion tank.
NC Miata Hub Upgrade Options (Front and rear)
A known failure point on the NC Miata when driven on the track at aggressive paces on highly sticky rubber are the hubs, both front and rear. I've written about this to great length in a post here, but here's some general information.
In the front, the easiest solution is to convert to RX8 front hubs. It's a simple enough bolt on procedure and will utilize the notably more robust RX8 parts which are meant for a notably heavier car. People have documented good luck with these at the track, but it is worth noting you want to get genuine MAZDA OEM parts, as other providers have yielded inconsistent results. Prices as of mid 2023 range around $500 a set. See the parts at Goodwin Racing.
In the rear the solution is not as simple, although the situation is evolving.
The accepted standard prior to mid 2023, was to run a full RX8 hubs and spindle rear swap. You can get more informaiton about that here on the miata forum. It's involved, not cheap, involves finding donor parts or buying all new quite expensive parts along with mixing and matching parts between the RX8 and the NC Miata. This is definitely not a simple bolt on. This setup though has been track tested with pretty good results. Professional install with all new parts runs about $4000 or so.
A new solution as of mid to late 2023, is that Mazda has made a more robust hub and bearing available that is significantly less intense to install than the RX8 setup. The part numbers are:
Flange 0000-04-5530
Bearing 0000-04-5531
Some folks claim to have track tested these already and have had great success. Not exactly sure how they pulled that off since the information is just barely getting out there now, but apparently they did or they are fibbing to just encourage adoption. Parts costs for this setup is around $1000 without shipping, as per this forum post. The part numbers are also confirmed in the new MX5 spec Miata Parts list.