Lightweight Miata Flywheel & Clutch
Posted: Mon Aug 26, 2019 2:20 am
I'm going to be swapping a transmission in my Miata sometime soon. Or soon-ish. No hurry. And if you know me, you know I like to shave weight where I can, especially with regard to spinny bits. And, I did make some extra money this summer...
I feel like I'm sort of recreating my first Miata in a way. I liked a lot about the mods I did to that car, and learned a lot from it, and from other Miatas that I've played with since.
With that in mind, I'm shopping for a lightweight flywheel. So. Many. Choices.
First some background for the non-Miata people playing the home game. All NA (90-97) Miata and NB (99-05) Miata flywheels are interchangeable. They'll all bolt to the engine and slide onto the transmission, and function in every way that they're supposed to. What you need to know:
- 90-93 1.6 Miatas used a smaller clutch (200mm or 7-7/8"), thus a smaller flywheel mating surface, and all lighter weight.
- 94-05 1.8 Miatas all used a larger clutch (215mm or 8-1/2") with a heavier flywheel. There were some differences in some of the later NB flywheels, but they still bolt up
- And the important part -- if you use a 1.6 flywheel, you must use a 1.6 clutch. 1.8 flywheel, 1.8 clutch.
- Worthy of note, a 1.6 setup, in addition to being lighter, the clutch assembly is a smaller diameter, so much of the weight is closer to center. Lower "moment of inertia". Just a fancy way of saying that the weight is in a better place so that it has less effect on acceleration/deceleration. As long as a 1.6 clutch can hold the torque that you need, it's going to spin up faster than a 1.8 clutch.
Now that we've cleared that up...
There are some CHEAP options. You can get a Chrome-Moly 10-pound 1.8 flywheel on eBay for $168 shipped. Is it going to be perfect? Close enough? Will bolt holes have to be re-tapped? Will they even be in the right place? Risks you take with cheap eBay crap. I want to say that I fitted an "F1" brand eBay flywheel to something... was it Fred? But, I'm not at all in the mood to do and redo on this project. Just wanna get it done and be happy. So, I'm leaning toward not cheaping out on the FW.
The pros of going that route would be that it would be dirt cheap and simple. I could get that and a stock replacement clutch disk and a couple bearings and be done. 8-pound reduction in rotating mass for under $300. Pedal effort would remain 100% stock. It would work.
But, in addition to the iffiness of eBay parts, I know that I can save another 2-3 pounds just by going to a 1.6 flywheel and clutch setup. Lighter is better. There are those who say you can go too light, and they're probably right. But, I've had lightweight 1.6 clutch setups on several Miatas and ALWAYS loved it. The lighter the better. Just give a clutch that's not gonna kill my leg, and can be modulated.
And there lies the problem with putting a 1.6 clutch behind a 1.8 engine. The stock 1.6 clutch tops out at about 130 ft/lbs. The 1.8 in my '99 is pushing around 140 ft/lbs. Would probably be adequate for mild street use, but to use a 1.6 clutch with a 1.8 for autocross... I'd need a clutch upgrade.
I have experience here. Both with cars that I've owned, and other cars that I've driven. Things I know about Miata clutches:
- The stock pedal feel is nice. Engagement is smooth and quiet. Good reasons to stick with the 1.8 clutch... but, they're heavy!
- A Spec Stage 2 clutch has a very slightly stiffer pedal. The Kevlar clutch disk gives is a smooth and quiet engagement. And the 1.6 version holds like 230 ft/lbs. Plenty for my purposes. Sucker is expensive, though. But, it does have a lightweight pressure plate option... oooh, MORE lightness!
- An ACT HD clutch has a very HEAVY pedal. Engagement is smooth, but quick and authoritative. I actually LIKE driving this clutch, but after a few weeks, my left knee hates me. It's a bit much.
- Puck clutches are a good way to get more torque capacity without increasing pedal effort. But, they invariably have very on/off engagement characteristics. I could live with it for a race car. But, this is a street car.
- Another thing I've learned is that unsprung clutch disks make for a lot of noise and vibration, and a VERY harsh engagement. Not gonna do that again.
All this led me to SuperMiata (949Racing) clutches. They seem to have done a great job of designing a clutch pressure plate and disk setup that holds ample torque without increasing pedal pressure much. I mean really well-designed, and well-built. They have a 1.6 clutch that will hold 220 ft/lbs. The complete kit (pp, disk and bearings) is $309. And they'll add an 8-pound aluminum flywheel to the mix for $289. (compared to well over $400 for a Fidanza) So, for about $600, I could cut flywheel weight by 10 pounds, clutch weight by another 2-3 and get that tasty low-inertia 1.6 clutch size.
It just might be enough to make up for the weird gearing setup that I'm ending up with.
Sooo... $300 more than the minimum I could spend to get a lightweight 1.8 flywheel. But, honestly... it's still less than I spent for a similar setup nearly 15 years ago. And the more I read reviews on this exact flywheel and clutch kit, the more I like it. It's just what I need.
I feel like I'm sort of recreating my first Miata in a way. I liked a lot about the mods I did to that car, and learned a lot from it, and from other Miatas that I've played with since.
With that in mind, I'm shopping for a lightweight flywheel. So. Many. Choices.
First some background for the non-Miata people playing the home game. All NA (90-97) Miata and NB (99-05) Miata flywheels are interchangeable. They'll all bolt to the engine and slide onto the transmission, and function in every way that they're supposed to. What you need to know:
- 90-93 1.6 Miatas used a smaller clutch (200mm or 7-7/8"), thus a smaller flywheel mating surface, and all lighter weight.
- 94-05 1.8 Miatas all used a larger clutch (215mm or 8-1/2") with a heavier flywheel. There were some differences in some of the later NB flywheels, but they still bolt up
- And the important part -- if you use a 1.6 flywheel, you must use a 1.6 clutch. 1.8 flywheel, 1.8 clutch.
- Worthy of note, a 1.6 setup, in addition to being lighter, the clutch assembly is a smaller diameter, so much of the weight is closer to center. Lower "moment of inertia". Just a fancy way of saying that the weight is in a better place so that it has less effect on acceleration/deceleration. As long as a 1.6 clutch can hold the torque that you need, it's going to spin up faster than a 1.8 clutch.
Now that we've cleared that up...
There are some CHEAP options. You can get a Chrome-Moly 10-pound 1.8 flywheel on eBay for $168 shipped. Is it going to be perfect? Close enough? Will bolt holes have to be re-tapped? Will they even be in the right place? Risks you take with cheap eBay crap. I want to say that I fitted an "F1" brand eBay flywheel to something... was it Fred? But, I'm not at all in the mood to do and redo on this project. Just wanna get it done and be happy. So, I'm leaning toward not cheaping out on the FW.
The pros of going that route would be that it would be dirt cheap and simple. I could get that and a stock replacement clutch disk and a couple bearings and be done. 8-pound reduction in rotating mass for under $300. Pedal effort would remain 100% stock. It would work.
But, in addition to the iffiness of eBay parts, I know that I can save another 2-3 pounds just by going to a 1.6 flywheel and clutch setup. Lighter is better. There are those who say you can go too light, and they're probably right. But, I've had lightweight 1.6 clutch setups on several Miatas and ALWAYS loved it. The lighter the better. Just give a clutch that's not gonna kill my leg, and can be modulated.
And there lies the problem with putting a 1.6 clutch behind a 1.8 engine. The stock 1.6 clutch tops out at about 130 ft/lbs. The 1.8 in my '99 is pushing around 140 ft/lbs. Would probably be adequate for mild street use, but to use a 1.6 clutch with a 1.8 for autocross... I'd need a clutch upgrade.
I have experience here. Both with cars that I've owned, and other cars that I've driven. Things I know about Miata clutches:
- The stock pedal feel is nice. Engagement is smooth and quiet. Good reasons to stick with the 1.8 clutch... but, they're heavy!
- A Spec Stage 2 clutch has a very slightly stiffer pedal. The Kevlar clutch disk gives is a smooth and quiet engagement. And the 1.6 version holds like 230 ft/lbs. Plenty for my purposes. Sucker is expensive, though. But, it does have a lightweight pressure plate option... oooh, MORE lightness!
- An ACT HD clutch has a very HEAVY pedal. Engagement is smooth, but quick and authoritative. I actually LIKE driving this clutch, but after a few weeks, my left knee hates me. It's a bit much.
- Puck clutches are a good way to get more torque capacity without increasing pedal effort. But, they invariably have very on/off engagement characteristics. I could live with it for a race car. But, this is a street car.
- Another thing I've learned is that unsprung clutch disks make for a lot of noise and vibration, and a VERY harsh engagement. Not gonna do that again.
All this led me to SuperMiata (949Racing) clutches. They seem to have done a great job of designing a clutch pressure plate and disk setup that holds ample torque without increasing pedal pressure much. I mean really well-designed, and well-built. They have a 1.6 clutch that will hold 220 ft/lbs. The complete kit (pp, disk and bearings) is $309. And they'll add an 8-pound aluminum flywheel to the mix for $289. (compared to well over $400 for a Fidanza) So, for about $600, I could cut flywheel weight by 10 pounds, clutch weight by another 2-3 and get that tasty low-inertia 1.6 clutch size.
It just might be enough to make up for the weird gearing setup that I'm ending up with.
Sooo... $300 more than the minimum I could spend to get a lightweight 1.8 flywheel. But, honestly... it's still less than I spent for a similar setup nearly 15 years ago. And the more I read reviews on this exact flywheel and clutch kit, the more I like it. It's just what I need.
Nope. Not a project.