Miata Turbo Forum - Boost cars, acquire cats. - The definitive lighten your stock flywheel thread

I'm trying to do something impossible but not new with my 94:
Build a better than stock car for as cheap as possible without sacrificing quality.

This led me to consider the flywheel. Lightweight flywheels are a notable improvement for most, and I wanted in on the fun. Paying 300+ for a less known brand or 400+ for a known brand didn't fit my build idea. Searching around led me to the idea of lightening my stock flywheel.

Stock NA flywheel: 19.3 lbs (pic 1)
Stock NB flywheel: 17.15 lbs (pic 2)

They both have an inertial weight ring that can be machined off (pic 4) with no affect to the function of the flywheel and it is significantly thinner on the NB style, resulting in the lower stock weight. I decided to machine the NB one down so that even if little weight could be removed, I would be lighter than my original stock NA flywheel.

I have free access to a machine shop so my machining cost was zero, but I have seen estimates in my forum crawling of anywhere from $20 at a brake rotor shop to $100+ at an actual machine shop.

After machining I had my NB flywheel down to 15.65 lbs.

Wanting to stay safe and keep my ankles, I set out finding a shop that could balance my less than scientifically ground down flywheel. This turned out to be the most difficult part. In my neck of the woods there are a lot of shops oriented towards oil rig work that balance rotating assemblies, but did not feel comfortable taking on my project. My suggestion is to either become or already be friends with someone at such a location, or you will have to go to a dedicated automotive shop that most likely does performance work since they will be more likely to have the equipment to do this. One quirk to the place I found was that they could not "free balance" my flywheel, but if I had something else to give them that I knew was balanced, they could balance the lightened one to the same balance as it. I'm not sure if this is unique to the shop I found or if that is to be expected. Anyways, I was fortunate enough to have the flywheel out of my NA that I knew functioned perfectly that they could use as a base line for balance. After a cost of $160 and 3 days, I had a balanced and resurfaced flywheel. In this process my weight came down a little bit more to a total of 15.55 lbs (pic 3).

So in all, I got almost 4 lbs (3.85) off from my original weight for a cost of $160.

Installed and driving, I can't give a completely honest impression since the car had been out of commission for about 3 months and I also installed a VVT engine at the same time, but it certainly feels a little peppier.

Would I do it again? Absolutely. Even if the end result wasn't huge, I learned a lot and it makes my car just a touch more unique. If you have an NA and don't want to go through all this trouble, I would at least source an NB flywheel to save almost 2 lbs.