We are collapsing (SLIPPING) clutch pressure plate(s), how?
 

Lemons car. VVT engine + fresh (1 and half races) 1.6 clutch + 6 speed gearbox this year. rusEfi ECU :)

After 4 racing hours this Saturday not much was getting to the rear wheels above 4000 rpm. Minor clutch smell. We were expecting to see a destroyed clutch but we've found that the clutch was perfect while the pressure plate was collapsed by maybe 1/8 of an inch comparing with another one we've borrowed from a different team. It was simply not pressing the clutch against the flywheel, the shiny surface is deeper than it should be.

After the swap of both clutch and pressure plate and 6 more hours of racing this MIGHT have started to happen again - still need to remove the gearbox. We've also found our old pressure plate from last year while we were on 1.6 engine and 5 speed gearbox and it also looks somewhat collapsed - less collapsed than the failed one but more collapsed than the replacement used we've got from another team. I could be making up the Sunday problem and I could be making up the problem with the old one - but the one on Saturday has definitely failed.

Any ideas what could be happening would be appreciated.

4 hours non stop racing might be heating it up to the point of deforming?

Interesting that you mention heat. We have that shiny eBay header and the heat gets to my right feet if I get too close to the transmission tunnel. On the other hand I am sure we are not the only one miata running endurance racing, are you saying our tune or engine are running hotter than usual?

double derp

any unusual TO bearing wear? is the clutch slave cylinder throwing too far, putting undue stress on a really hot part? not entirely sure that would effect clutch to PP force though..

PP force so strong, you double posted it :D

But yeah, I wouldn't think the heat from a header would cause this. More heat from friction or somtehing

OEM Exedy PP or some eBay/F1 RACINGGGGG garbage?

OEM Exedy PP, not any random shit

Make sure the flywheel isn't an odd part, replace the pilot and TOBs for good measure. I have a hard time believing you found two bad Exedy PPs, but I guess that's possible. I would call Exedy to see if they are aware of something, but I'd also expect them to say "no, its something else".

I'd blame some improper flywheel machining, seeing as though it sounds like the only variable that hasn't changed.

Is one of your drivers riding the clutch? Could be putting stupid amounts of heat into it

that could be checked by inspecting the fw for major hot spots and cracks

We had a driver do this in our first enduro. Stock 1.8 flywheel/PP/disc. We eventually started hearing it as he went down the front straight, he was getting back on the gas far before letting back off the clutch. Poor radio communication led to him coasting it into the pits with essentially an overheated/glazed clutch. Once removed we saw zero damage, TO/pilot bearing was quiet, disc was just shiny glazed and PP had lots of heat spots. Another stock clutch on that same flywheel with decent shifting lasted dozens of hours more.

My point being that, riding the clutch pedal will typically destroy TO bearings, crappy shifting will typically glaze the disc and burn the PP, but from what you're describing I'm suspecting poor installation or machining.

So we are assuming that what's happening mechanically is that the PP diaphragm spring is getting over-exerted and thus changes shape permanently- correct?

Seems odd for it to do that, though—why would it "take a set" after a few hours racing, when most PPs don't do that over their lifetime? Would a lifetime of clutching be less pedal time than a few hours?

A lifetime of normal clutching would not raise the temperature of the parts in question to nearly as high a temperature as a few hours of riding the clutch continuously, or a few hours of operating the car on a track with some combination of mis-adjusted / mis-aligned something that's causing the same effect.

Consider a piece of 1/2" steel rod, and an oxy-acetylene torch. If you wave the torch at the rod for a second or two, then take it away for 60 seconds, you could repeat this process until you burn through a whole tanker-truck of gas without ever harming the steel rod. But if you hold the torch in place continuously, that rod's gonna deform pretty quickly.

So the part where I cannot touch the transmission tunnel next to throttle pefal while wearing my cheap racing shoes - is that normail temperature of that spot while racing in CT in mid August? 80sF day I guess.

In my experience, that's normal for driving a Miata on the street.

Something went wrong with logs and I do not have Sunday logs to confirm that we were slipping clutch again, but two drivers believe this was happening. Not sure why would this happen on this race and not the previous one - same setup pretty much everywhere, the only different is the shorter track (Thompson VS NJMP previously) so probably more shifting per minute?

Anyway, what should be my next step? Is Fidanza 161161 the clutch to go with? What is the (racing?) clutch for our well... racing I guess we have to call it application?

What disk you guys running? IDK what the deal with collapsing the PP is, never seen that in any of my Miata's, but certainly a short track with more shifting will/can overheat a non puck disk.

I like the feel of oem PP with the ACT 4puck sprung, running that in the vvt SM.