As I plan for each new upgrade to my cars (plans, HA!) I suspect a new clutch will be in order for the Miata. Obviously a lightweight flywheel is in the plans but my question is the clutch itself.
An OEM style clutch is a full disc of friction material. But some "upgraded" units are six or four pads of material with space between each. Why? How can loss material hold better if the clamping force is equal?
Help me out here, I just don't get it.
Don't know the technical reasons, but it does work. My 70 duster, 425whp, 4 speed, and wrinkle wall slicks grips just fine with a spec stage 2+ .full face on one side, pucks on the other.
A puck clutch usually has a more grabby material, so they're harder to engage smoothly. But they have less rotating mass than a full disc clutch.
KyAllroad wrote: As I plan for each new upgrade to my cars (plans, HA!) I suspect a new clutch will be in order for the Miata. Obviously a lightweight flywheel is in the plans but my question is the clutch itself. An OEM style clutch is a full disc of friction material. But some "upgraded" units are six or four pads of material with space between each. Why? How can loss material hold better if the clamping force is equal? Help me out here, I just don't get it.
Never thought about it til now....
I guess the normal force goes up due to the pressure being the same but the area being less (pressure = Pounds / Square Inch). If the pressure (psi) is the same and you lower the area (inches), force (pounds) goes up.
I am an engineer and I think I am botching this badly....
From what I understand, the clutches with the pucks have a much more aggressive material on them so they can have much less material and still hold more power. I autocrossed a 350Z with that kind of clutch, and it's a pain in the ass to just start from a stop at normal speed since it grabs so fast. It stalls out when you try to operate it at a normal rate. I've read recent SCCA Sports Car mag articles about it, and most people don't need 6 puck clutches. Often, OEM is good, or even a slightly more aggressive clutch without pucks and an OEM pressure plate is good enough. The article also stated that a good performance clutch system is one with 2 or 3 clutch discs so they can be smaller, not super aggressive friction material, and easy to operate on the street.
The multi-puck design is really more for cooling than anything else, the individual pucks cool faster than a full-disc material type. When combined with more grabby/aggressive pad material they can hold better too.
If you don't need more clamping force and aren't having problems with your clutch getting gooey, stick with an oem-spec or "stage 1" (slightly grabbier full-disc material and slight clamping force increase) clutch. No sense giving your leg a workout and making the car easier to stall for no reason.
Friction is independent of surface area. With the same pressure plate, halving the amount of friction area will double the amount of PSI on that friction area.
This lets you use things like sintered metals as the friction material, the added PSI allows them to grip well, and the fact that they are a metal instead of a resin-bonded fiber means that you aren't going to overheat them into fluff if it slips a lot.
I like puck clutches. I ran one for a long time in the RX-7. The engagement was a little tricky but nothing you couldn't adapt to. Best was stock pressure plate and copper puck clutch, nice and light pedal and plenty grippy and NO chance of the friction material coming apart, a failure I have had twice with regular clutches.
Make sure you get a sprung centersection. Solid disks are transmission killers. The springs take up the micro shock loads that eat gears and twist shafts. My puck disk was unsprung, I ate many many transmissions with it. I eventually deliberately scrapped it so that I wouldn't be tempted to use it again.
Now I have an ACT with an organic disk and a firmer pressure plate. The pressure plate makes throwout forks crack and pivot balls break on a depressingly regular basis, even with reinforcement. My next clutch will be a stock pressure plate and a sprung 6-puck.
Heres what i did with my miata and was super happy, i got an ebay chromoly flywheel and an "upgraded" clutch set which was an exedy oem disk and a rx7/b2300 pressure plate. They sell them like that as a kit idk what they call it, stage one or something. But thats the budget setup id go with, cost me like $370 for the lot and i was very happy with it and im pretty particular about things and over researched that one, it was a smidge heavier but if someones never driven a miata before they wouldnt notice it wasnt stock. If you want to spend more get the flyin miata happy meal, its amazing but $700 or so.
Takes from the setup i had, grabbed like stock, felt like stock, didnt slip with 205 ho hos unlike stock. Supposedly good to 200ft/lbs, i was planning a turbo that didnt happen but at least i wasnt left with an omg stage 11 cluch leg
I haven't had to do the clutch on my miata yet, so I don't have any actually experience on the matter, but when I asked before I was heavily recommended the Flying Miata Kit. They have various stages of clutch too depending on how much, if any boost, you are running. 1.8l NA/NB Clutch Happy Meal
Ever upgraded your brakes with better pads? Same thing with a clutch disc.
Do understand that the magical super grabby clutch is harder to control on engagement. So don't go overboard with the likes of a true racing clutch. For a car on the street, you really want that disc waviness and such, so you can take off slowly and without lurching or spinning the tires.
I think it has been said already,
Less surface area in the upgrade disks equals:
Judging by some of the previous replies, there is apparently a lot of misinformation out there about clutches. Lets set the record straight...All else being equal:
Less friction surface area does not change the normal force or holding power of the clutch. Surface area is irrelevant in determining the actual friction force, although the faster ramping of pressure on the friction material from the reduced surface area will cause feel more aggressive. Less surface area does mean less volume/mass/inertia. Reducing inertia is a good thing. However, less mass means it will heat up faster when subjected to slippage, while the reduced surface area means it will not be able to conduct the heat as quickly away into the flywheel and pressure plate. Airflow past the clutch disc is negligible. So while pucks may be cool, they are not cooling. Less volume also means that it will wear out faster.
Note that dedicated racing clutches, pretty much regardless of racing application, use what are essentially full faced metallic discs.
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