If the holes Porsche use are smaller, then that's even worse. The smaller the diameter, the more likely you'll se stress cracks pop up. Plus a cast hole is worse since the surface finish doesn't help the situation either. In order to prevent stress cracks as much as possible, the surface of the holes should be as smooth as possible and the edges either round over or chamfered.

 

its so many different opinions on this stuff... I know what I'm going to do though... slotted rotors

 

I'll try and find the article

I really don't see how you can say that a smaller hole is more prone to stress cracks or how drilling a hole in a solid rotor is a better idea than having it cast that way. I'm also pretty sure that the porsche rotors are chamfered in some way

If you can back it up thats cool but I am going to have to disagree untill then


edit: here is what I got

1) The holes are cast in giving a dense boundary layer-type crystalline grain structure around the hole at the microscopic level as opposed to drilling which cuts holes in the existing grain pattern leaving open endgrains, etc, just begging for cracks.

2) The holes are only 1/2 the diameter of the holes in most drilled rotors. This reduces the stress concentration factor due to hole interaction which is a function (not linear) of hole diameters and the distance between them.

3) Since the holes are only 1/2 as big they remove only 1/4 as much surface area and mass from the rotor faces as a larger hole. This does a couple of things:

It increases effective pad area compared with larger holes. The larger the pad area the cooler they will run, all else being equal. If the same amount of heat is generated over a larger surface area it will result in a lower temperature for both surfaces.

It increases the mass the rotor has to absorb heat with. If the same amount of heat is put into a rotor with a larger mass, it will result in a lower temperature.

3) The holes are placed along the vanes, actually cutting into them giving the vane a "half moon" cut along its width.

This does a couple of things:

First, it greatly increases the surface area of the vanes which allows the entire rotors to run cooler which helps prevent cracks by itself.

Second, it effectively stops cracking on that side of the hole which makes it very difficult to get "hole to hole" cracks that go all the way through the face rotor (you'll get tiny surface "spider cracks" on any rotor, blank included if you look hard enough).

 

I heard of this too, my dad's 08 z06 has the drilled rotors.

 

Let's start:

1. While that's true, remember a rough surface finish, indicative of casting, is also a stress raiser. This is why critical parts are polished to remove these stress raisers.

2. This is false. The smaller the radius, the more of a stress raiser it is. However, this is assuming that the holes aren't so large or close to each other making the material in between the holes too thin. This is why, for example, when slots are made in metals, the ends are usually a half-circle, and not square. Also another reason why you find filets on the edges of critical parts.

 

Tap on your brakes a few times when you go through water

 

True, but when you have an oh-**** moment, you generally don't have time to tap the brakes a few times.

 

I always give the brakes a few taps after going through a puddle to get them dry so I don't have the oh **** moments

 

lmao...don't race in the rain

 

I race in the rain. SCCA auto-x includes combat conditions at no extra charge. If you think you can't drive fast in the rain in a racing situation you're inexperienced. In my experience you can go 90% as fast in the rain as you could in the dry. Sometimes you can even drive a little faster when it's wet, depending on the track.

 

I was talking about street racing and I was also moving forward from a previous post of infoming bassman97 not to race in the rain if he can't handle the breaking after his "oh **** moments".

 

I don't race. My oh **** moments involve rubber-neckers stopping to look when traffic is moving 70+.