Clutch & Flywheel Questions: Ford 2.0 Ecoboost + NC Miata 6 speed

So I'm working on combining a 2.0 Ecoboost and a NC (2006-15) MX-5 Miata 6 Speed Transmission and putting it in a car it has no business being in.

Lots of good info on here (thanks to TVRScott and his awesome build thread) but I have a few specific clutch & flywheel questions, mostly on the Miata side.

Couple of relevant notes:

- Engine will produce around 360 lb-ft

- Transmission likely wouldn't sustain that normally, but car will be severely traction limited

- Intended use is mostly street driving with some abuse thrown in (again, traction limited)

Conventional wisdom here is to use a Miata clutch, flywheel, slave cylinder, starter, etc. as the stock Ford pressure plate will not clear the clutch fork and/or bell housing. However, I happen to have a shiny twin disc clutch, lightweight flywheel, and new Ford starter laying around: Last night I mocked them up and physically, everything fits...but...

Am I going to hate my life trying to drive on the street with this 7 lb flywheel and this overly aggressive clutch? (clutchmasters 725 series twin disc) I'm assuming there will be lots of chatter, rough engagement, etc.

Assuming I will need to start over with Miata parts, I have a couple options from both ACT or Clutch Masters.

What I need help deciding is if it makes more sense to go with an organic disc (rated somewhat under the engine peak torque) for driveability, or straight to the 6 pad disc for durability. Examples from ACT here:

https://www.advancedclutch.com/zm4-hdss-act-heavy-duty-performance-street-sprung-clutch-kit

https://www.advancedclutch.com/products/transmission/zm4-hdg6-act-heavy-duty-race-sprung-6-pad-clutch-kit

Thanks in advance!

Puck clutches suck on the street. That's a hard no.

Twin plates can be really nice. Their weak point (aside from cost) is that they can be fussy if they get hot. I'm generalizing here, but there's nothing about a twin plate inherently to run away from in my experience. I'd talk to Clutchmasters about maybe some different discs for that to make it more streetable.

In reply to Keith Tanner :

Good point Keith, I didn't think about changing the discs out. In my initial conversation with Clutchmasters they seemed to think an FX400 (also a 6 puck) was more appropriate for this build. The concern regarding the 725 twin disc I already have was pedal stiffness/effort in addition to general streetability.  
 

I'd like to use a stock pedal box, master, slave cylinders if possible so too stiff of a pressure plate could be problematic. 

So a little more investigation and it appears I have the FX725 “Street and Race” version – 1 ceramic rigid disc, and 1 fiber tuff rigid disc:

Not much specific info on their site but the description is "Because of the minimal rotational mass the FX725 isn't ideal for the street but with improvements in friction material over the years we have been able to create a solution that can handle occasional street driving. The FX725 is designed to hold tremendous horsepower and torque, while maintaining reasonable peddle pressure to operate on the track."

Still sounds maybe too agressive for what I'd like to do with this car but I'll follow up with them on any other disc options.

In addition to the low inertia, exacerbated by the lightweight flywheel, race clutches have a narrower engagement window. So even with organic discs they still tend to be a bit of an on/off switch, while also heating up and wearing out more quickly when you do slip them. By design, race clutches are happiest when you slip the tires, not the clutch.

The idea behind a twin plate clutch is to get more torque handling ability - all else being equal - without requiring more force on the pedal, right? It shouldn't be a heavy pedal unless it was designed to be a heavy pedal. And in my experience, they can be quite progressive and easy to drive. This is all a matter of the right material and springs. My comments are based on a prototype kevlar dual plate setup, I don't recall who made it.

"Race clutch" is kinda like "race cam". It's not really a definition of a type, more of an intended use. Better to describe specific attributes like a puck clutch or different types of friction material or single vs twin plates. 

I had no issues with a 4 puck clutch and a 10lb flywheel behind a rotary.  

I like puck clutches because they don't need as much pressure plate force to work, and I like a very light clutch pedal.  They're fine to drive once you get the hang of it.  The engagement window is smaller, yes, but it's nothing that one can't learn to modulate.

Multi disk clutches in theory have a wider engagement window.  I've only driven two, a twin ceramic puck unit and a triple carbon unit. (Both in an STI; we took out the triple because it slipped a lot until it got hot, and installed the double)  Be mindful that multi disk clutches rattle a fair bit when disengaged.  It's not an issue, just disconcerting if you don't expect it.

The largest issue I had with 4 puck disks was getting a string of bent disks.  Not sure if damaged in shipping, or lackadaisical manufacture, or even a good natured attempt to widen the engagement window.  I want a very short engagement window.

The lack of a sprung hub would be a bigger concern to me than the twin disk or puck style friction material.  Will be loud, will be chattery, will eat driveline parts.

Keith Tanner said:

Race clutch" is kinda like "race cam". It's not really a definition of a type, more of an intended use. Better to describe specific attributes like a puck clutch or different types of friction material or single vs twin plates. 

Except that a race clutch has a totally different design to an OE style clutch, and was originally designed from scratch specifically for racing, and have a wide variety of options too choose from to be trailer to a specific application. A single disc version of racing clutches exists. All else equal, a single disc race clutch drives effectively the same as a multi disc, just with less torque capacity. An OE cannot be made all else equal, and has different inherent characteristics. Sure a race clutch can be made somewhat streetable despite it's design, just like an OE can be made totally unstreetable despite it's design. The reasons behind why for each style has to do with their fundamental design differences and limitations there in. That's why, having engineered race clutches (and flywheels) professionally in a past life, I find race clutch to be the more authoritative generic term. If you really want to be pedantic about it, then you also need to specify diameter along, spring stiffness, and sprung vs unsprung hub, in addition to number of (not just multi) discs and cover style (OE/race), and material to provide accurate feedback. Carbon discs are also a totally different animal too metallic, ceramic, or organic, so I would make too many generalizations or assumptions based only on experience with that.

Right, it's a definition based on intended use. A "race clutch" is a clutch designed for racing, but can you point to one specific thing that would help you identify a "race clutch"? The fundamental design is, as I understand, basically the same. It's about all the choices made along the way. I don't believe a twin plate has to be a race clutch, for example. It's more likely to be, sure, because it has certain attributes that are more useful in a race application. But as I noted, my twin plate experience is with one in a very lightweight car with a high compression engine and I never found it difficult to drive. I also drove the same clutch in a car that weighed twice as much.

Unless there's something I'm missing, which is always possible.

In reply to Keith Tanner :

While it's really a spectrum, and there are always exceptions, I feel like clutches group pretty well into 4 main categories. 

1) OE style: Unitized construction, steel cover, integrated strap-driven pressure (and intermediate) plate(s), OE (generally 8.5"- 12") disc size, sprung hub available, OE mounting pattern compatible with OE flywheel, and OE spring finger configuration compatible with OE style release bearing (flat/radius face, height, and contact diameter). 

2) Race: Modular construction, aluminum cover, floating leg-driven pressure (and intermediate) plate(s), industry standard (5.5" or 7.25") disc size, no sprung hubs, mfg specific mounting pattern compatible with mfg specific flywheel, and industry standard spring finger configuration compatible with industry standard style release bearing that gets adjusted to the clutch height. 

3) Hybrid, many potential names: Substantially combines race/OE attributes. Example - Race clutch, but with strap driven pressure (and intermediate) plate(s), common larger (8.5", 10", or 12") disc size, and sprung hub available. 

4) Drag: Lever style.

When engineering a clutch, style and disc diameter are the first thing selected, and all other decisions are used to tailor it to the application. So when people (marketeers) say "multi" or "twin" disc, that may tell me 'probably not OE style', but not much else since it could literally be any of the diameters or other styles still. A 10" strapped, sprung, and organic, twin disc is a very different animal from a 5.5" floating, solid, metallic twin disc.

Race clutch, as defined above, is the minimum effective description of the OP clutch for me, with 7.25" race clutch next. Only after style and diameter are known does friction material (1/2 organic) and number of discs (twin) become particularly informative. That's why comparing clutches based on friction material and/or number of discs between different (or unknown) style and diameter is even more apples and oranges IMO.