How in the world do you keep doing this?

 

Perhaps I am to brakes what bbundy is to transmissions? I dunno.

Picked up a set of directionals from Andrew this morning.

Looking at the pattern of cracks, these are different from the usual heat/expansion/etc cracks. Those are usually radial, but these are almost tangential, it's as if the calipers are ripping the rotor ring off of the mounting tabs. Is it possible I'm getting the rotor so hot that the metal is losing strength?

--Ian

 

put codrus bundy and fae together and you have an unstoppable Miata destroying trifecta

 

I'll handle the torsens.

 

and thumpetto will handle the megasquirts and shifters, and pat the axles

 

I call fasteners!

 

So this was my favorite track day club -- no run groups, track is open 9-12 and 1-5, go out when you want, come in when you want. I'd been out for 8 or 9 laps, it was running low on fuel (5 gallons left and it's starving in 6 -- a fast left). I came in for fuel, went straight back out, did 3 laps and was catching a Porsche. Smelled brake fluid, backed off, smell went away. Did another half lap and it oversteered during steady state cornering. Back at MRLS 2010, that was the first indication I had of a coolant leak, so I backed way off and brought it into the pits to check it over. Didn't find any leaks, but the saw the rotors and called it a day.

The scary thing is that if it hadn't done that oversteer thing (still not sure why -- might have been the rear tire pressures getting a tad high) I probably wouldn't have noticed for a while. That driver's side rotor is cracked a third of the way through -- how much further would it have gone before failing?

--Ian

 

I thought Turbofan was ripping the rotors from the tabs in a similar fashion

 

Nope. I don't brake nearly as much as he does :P

 

In all seriousness, when we were comparing data at MRLS a year and a half ago, his speeds on the straights were 5-10 mph faster than mine, and my cornering speeds were about the same; slightly higher through some corners. The amount of power his car makes is eye-opening.

My cornering speed through turn 6 was like 6 or 7 mph faster than his, and his peak speed up the hill through 7 was some 9 mph faster than mine. That's some serious zoom zoom. Hard on brakes.

 

Those are the straight vane 11.75"? What pads are you using?

Also somethings wrong if you're fuel starving a Miata with 5 gallons left in it.

 

Straight vane 11.75s, yes. Pads are Hawk DTC-60s. Just pulled the brakes apart, the pads are toast as well. Seriously, after 16 hot laps at Thunderhill the brakes look as bad or worse than they did after the whole weekend at Laguna. And that's with bigger brake ducts...

As for the fuel system, people keep saying that but that's what's going on. I've had the fuel system apart, replaced the sock with a brand-new OEM one, everything in there looks fine. Turbofan's car does the same thing, IIRC. If you go back a couple pages it's pretty clear from the data logs that the fuel pressure sags when powering out of fast left-handers. (posts 634 & 635). Maybe it's a return vs non-return fuel system thing?

--Ian

 

Here's the driver's side rotor after taking it off the car:



Savington suggested checking to make sure that the the holes on the hat are aligned properly, because there have apparently been one or two cases where they weren't, and that would make for all kinds of weird stresses on the rotors. I haven't done that yet.

--Ian

 

There's a big stress riser where the crack starts from that radius. The design of the rotor is contributing to the failure since the rotor necks down there and has a radius there too. That's a design problem IMO, or you at best the design is not suited for your use. But it's my opinion brake rotors shouldn't crack under use before they wear out.

 

Its my opinion that brake rotors shouldn't crack at all.

 

.

 

I have the fuel starvation too, planning to rebuild to return system with manifold reference. If that doesn't work I'll go ahead with some e85 resistant tank foam.

Love this build, using the same turbo for my rebuild, hoping for similar results.

 

Turbofan has a return system. Codrus has a manifold referenced system.

 

Looks like peak temperature + braking torque + stress riser = cracks

My guess is the directionals will increase internal airflow by 10-15%.

Barring that, it's time for this!

 

Well, there goes that theory then.

--Ian