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.