I am talking about the direction on drilled/slotted rotors. I have seen pics with the slots angled forward (/) and also with them angled toward the rear (\) of the car. (To me slots angled rearward (\) project a forward motion to the car when parked.)
Does it make a difference in braking efficiency by the direction they are installed in?

 

The internal vanes determine the direction of rotation. The vanes should rotate so that air is pulled from the hub area and vented from the edge of the rotor.

On the left rotor the vane at the top should be at this angle .... /

 

Do all rotors have curved vanes? If not, would it still make a dfference in the slot direction? Excuse my ignorance on this.

 

Not all rotors have vanes in them. Rotors with the vanes are often referred to as "vented", but there are rotors that are "unvented" ....

http://www.cachassisworks.com/DataSh...336_DS_WEB.pdf

Generally unvented rotors are used in applications (such as drag racing, or VERY light vehicles) where heat build-up in the rotors is not an issue.

Vented rotors come in all kinds of configurations .... curved vanes, straight vanes .... many vanes, a few thick vanes .... all seems to depend on the designer's philosophy on the rotor being a heat sink versus being a heat radiator.

The slots cut into a rotor are another area where designers differ .... some want the slots to "flow with" the rotation of the rotor, while others believe that by reversing the slot direction it improves the ability of the slot to "clean" the pad as it sweeps over the slot.

Finally, there are those who argue (I'm one) that brake pad material science has reached a point where the issue of "off gassing" from the pads is no longer an issue, and therefore drilling/slotting rotors has no benefit, and in fact simply removes metal that should be part of the "heat sink" ability of the rotor.

Long ago I read an article from a brake engineer who really hit the nail on the head. He pointed out that a brake is a way to transform the energy of a car's forward speed to heat energy. All a brake is about is generating, and then dissipating, heat.

 

Thanks for the education! I am looking at the drilled/slotted rotors to replace the originals. Honestly, just for cosmetic reasons. I've heard these rotors make a "whirring" noise under hard deceleration.
Is that true? Would the direction of the slots make a difference in the noise level of these rotors?

 

I haven't heard anything like whirrling noise. I have drill slots, but no noise.

The vanes determine the direction of rotation, not the direction of the slots. BlackZ06 is correct

 

All the drilled/slotted rotors I've seen (including mine from NAPA) were marked "left" and "right". No need to put a lot of thought into it, just read and follow the label.

 

While I agree, I have to add that Baer rotors actually have the vane's pointing forward, backwards from standard design.

The AC delco rotors I recieved had no labels, just p/n's. You can look up what p/n goes where.

 

I ordered some rotors. I'll see if they are labeled for what side they go on. The rotors appear to be straight fins. Is there a break in period for new rotors? Now, I just need to select a pad that does not put out too much dust. Any recommendations for a cruiser Vette?

 

I respectfully disagree. Even tho the holes and slots are angled forward at the top of the rotor the vanes inside the rotor are angled toward the rear.

 

By the way, nice rotors!

 

marked left, right...and to think i thought that they were telling you which hand to use when mounting the rotors....DOH

QUOTE=hmsminnow;1564849295]All the drilled/slotted rotors I've seen (including mine from NAPA) were marked "left" and "right". No need to put a lot of thought into it, just read and follow the label.[/QUOTE]

 

They are made both ways. You have to follow the internal vanes. If they are straight vanes it really doesn't matter....follow your philosphy. Otherwise pay attention to the internal vanes for direction. Internal vanes should be this direction / on driver side. Bringing air from the center toward the outer edge at speed.

 

The directon of the slots is manufacturer specific.
The internal vanes need to point rearward.


Mine clicked/whirred for the first 100 or so miles until the leading edge of the new brake pad got bedded in. Since then... NO noise.

 

You hit the nail on the head!!!!
Most of the better brands/manufacturers put a sticker or label on each rotor. Follow it. You CANNOT go by the slots on the pad face.

 

With modern brake technology, there is no need for "de-gassing" slots, so they are just for show. Brake efficiency also depends on total surface area of the rotor, and holes and slots just remove surface area that could be contacting the pad. How many race cars have you seen with drilled and slotted rotors?
Also, if look at C6 Z06 rotors, you will find that GM used the same rotors on both sides. Go figure.

 

Gees, I would kind of consider the C6 Z06 a "race" car.

Guess you answered your own question.

Do me a favor, touch a regular rotor after race session, or better yet watch them glow when they brake for a turn. That might be ok for 500 miles, but I bet it wouldn't hold up much longer. So yes, they are likely getting the best braking possible at the expense of the wheel bearings, pads and everything else they rebuild after a race. I'd rather have my brake rotors running at 120-200 degrees than 200-500 degrees.

Especially on the street.

 

What TEXHAWK0 is referring to is that, for a C5 for example, (any model) if you look at a set of rotors they are marked L and R because the internal vanes have to be cast going in opposite directions. Another way to say it is there are 4 unique part numbers for rotors on a C5.

For whatever reason, for the C6Z the rotors are interchangeable side to side because GM only ordered the rotors cast one way ... the rotors on the other side of the car are actually spinning "backwards" with the vanes drawing air in toward the hub ... not away from it. In other words there are only 2 unique part numbers for C6Z rotors .... front and rear .....

Hardly a race car set-up.

Finally, comparing how a race car is prepared to last the length of a race (John Force rebuilds his engine after driving a quarter mile .... ) doesn't really apply to a street vehicle where the manufacturer builds the engine to last a minimum of 100,000 miles .... but knows it is highly unlikely that either the tires or brakes that the car left the factory with will last that long .... some stuff (oil, tires, brake pads, rotors, etc.) are considered "wear items" and usually are excluded from a vehicle's warranty.