Looking to build your very own Spec Miata? In this article, we’ve summarized a few of the rules and addressed some frequently asked questions about shopping for donor cars. We talked to experienced builders and here’s what they say:
- Any year NA or NB Mazda MX-5 (1990-2005) with a manual transmission will work for building a Spec Miata race car (see rules here).
- Older cars tend to be less expensive and it is worth a spreadsheet to compare what an older and a newer donor will cost in total after conversion.
- A key thought to keep in mind is that many of the parts that don’t matter to race will need be replaced. Don’t pay for what you’re going to throw away.
- Another key thought is that finding a car with the right parts is great, but since parts can be replaced, spending more on a donor to “save money” on upgrades may not be wise.
- Either a manual car or an automatic car (converted to a manual gearbox) can be adapted to Spec Miata use.
- Depending on your budget, mileage of the donor may not be that important. You will be replacing most wear items for a top notch build.
- Similarly, cars with blown motors are acceptable because you’ll be replacing the engine.
- The frame/tub is the key item you are buying. You probably want an un-crashed car with no rust. Beware wavy chassis pieces or obviously bent bits.
- Cosmetic wear or damage can be your friend. Street cars buyers don’t want ugly, damaged parts like seats and steering wheels; you will be replacing these and the damage can save you money.
- You don’t have to run a limited slip differential (LSD), but it will improve lap times. There are 2 kinds of limited slip differentials depending on platform. The 90-93 NA cars came with a clutch pack style LSD, where the later cars 1994-2005 offered a Torsen helical gear set style differential. The 90-93 cars ring and pinion is smaller than the later 1994-2005 cars and can therefore be a little bit more maintenance intensive in racing environments. Most rule sets allow the 90-93 cars to upgrade to the later model Torsen differentials with the larger ring and pinions which tend to be far more robust and generally require little to no maintenance once installed.
- To find a donor with a TorsenLSD, look for a car with the 15” wheels, or simply add the LSD to your spreadsheet when deciding how much to pay.
Mazda also has a useful article on donors. Mazda adds:
Selecting a chassis starting point: wrecked, rebuilt, or road-ready?
The single most crucial step in deciding what donor would best suit your needs is being able to properly assess how much work you are willing to take on yourself, how much you will need to outsource, and the value of that.
Do you have the means to repair body work, suspension damage, or even repair rust? Or would it be better to find a mechanically sound car, road-ready, with fewer likely possible surprises along the way? This guide should help provide some insight as to price points, common issues, what to watch out for and sources where each could be located.
Wrecked / Salvage: (Average cost range $1,000-$4,000)
These can be some of the hardest to find, but most rewarding on your budget. The NA/NB chassis can still be found through a salvage outlet (such as Copart, IAAI or other insurance auctions) is not terribly difficult and can provide your donor chassis at quite the compelling cost.
Auction cars can be a wonderful source of a donor, but can come with some pitfalls. While not only slightly harder to come by, most auction cars will have a substantial amount of damage. Whether it was a wreck, fire, flood or who knows what else, you will have a large list of work before even starting on the parts and pieces to convert to spec racing. Also, make a point to read in to what dealer, auction, and delivery fees may incur with a salvage purchase. The car may be listed or sell at a certain price, but that is never truly your “out the door” cost. You also may need to “know someone” to get in the door at many auctions, especially those designed for dealers.
Other sources such as Craigslist and Facebook Marketplace can provide great outlets to pick up a donor at relatively low cost. Cars typically range in price ranges from $1,000 to $6,000. Examples have also been collected from these sites for as low as $500-$1,000 with blown motors, front-end damage, etc. But as with all private sales, these can be very sporadic and hard to find. Unfortunately, timing and luck will play a major factor.
Road-Ready: (Average cost range: $5,000 – $15,000)
So you want a clean starting point, with little-to-no unforeseen issues or expenses? Sometimes it is just easiest to find a good reliable driver. While initial cost tends to be much higher than the other options overall, the starting point you’ve provided yourself will be much easier to bring to a complete race ready vehicle as they tend to have lower miles, less abuse, and overall better condition from previous ownership. But it goes without saying, none of them will be perfect, make sure to take the time to go through the car thoroughly before purchase, as to catch anything that may have been missed in vehicle description.
Issues to watch out for:
Overall the NA/NB platform is a very reliable, sturdy vehicle; however, like every pre-owned vehicle, it could highly benefit you to inspect the car thoroughly before purchase.
Depending on the age of the car you’re considering, you may see some wear. Search for rust, but not just in the obvious, visible areas. Look under the carpet, if it will pull up; though, understandably, some sellers may not feel comfortable with you seemingly ripping up the carpet “just in case.” Look in the trunk around the brake light mounts, especially in parts of the country prone to rust.
Look at plastics under the hood. Parts like the factory plastic coolant expansion tank can give you clues as to how much detail has gone into the car’s maintenance. Often, this plastic begins to wear and may show its age. If it looks like it has been replaced, find out why – it may indicate a previously overheated engine. Not a huge deal if you’re installing a built race engine from one of the many engine builders, but still great to know!
The most important aspect of your donor car is likely the unibody. Whether it be a small wrinkle in the frame rail above the front wheel, or a bend in the unibody underneath the trunk mats, there are a lot of places you can skim over the car without noticing. Take extra time to ensure everything is straight, and the car matches the history given. The only other places to watch for unknown frame bending are underneath the car. The unibody of the NA/NB chassis requires a decent amount of under-body bracing. If the car has ever been bottomed out, or hit a bump wrong, there is the possibility of these brace mounts getting dented, beaten, or stripped.
There are many in the community that you can ask questions and get advice from. As with any advice, you get what you pay for so make sure the advice your getting makes logical sense to you and you should be fine. Be careful with online forums that have only a handful of people posting that present themselves as subject matter experts. Ask as many people and shops as you can to get a good overview of viewpoints on the topic.
The bottom line is that there are many ways to get out and get racing in a Spec Miata. Choose the path that works best for you and get racing!
