67King

Just want to verify my assumptions. Recenlty got a set of Turbo S brakes for my track car (944 turbo). Fabbed up some air ducts, put on the big brakes, and assumed I put them on correctly. Then I checked my street car, which is an 89 Turbo (therefore an S).

I had assumed that the leading edge of the vanes should be on the INSIDE of the rotor, to pull air from the middle, and extract it from the outside edge of the rotor. Therefore the trailing edge would be the outside of teh rotor. This is especially true when you run ducts to the hub. Problem is, my street car has them running the opposite way. It is pretty low mileage (64K), and the person from whom I bought it owned it since it was 2 years old and didn't really drive it hard. So I'm inclined to think it may have never had the rotors removed.

So am I backwards in the way the vanes go, did Porsche put them on differently from the factory (i.e. with no ducts), or did someone somewhere along the way get the rotors swapped on my street car?

Again, leading edge of vane should be on the inside of the rotor, and trailing edge should be on the outside is my going-in assumption.

Bill Verburg

Bill Verburg

not all rotors have curved or directional vanes, but if they do then the rotors are chiral, ie they have a left side and a different right side rotor, this digram shows a left side rotor. Note the counterclockwise rotation. The surface features such as grooves or holes may or may not match the internal design, In this case , not

plima

This is a recurring topic on Rennlist; here is a link that I think finally resolved the issue:
<https://rennlist.com/forums/996-gt2-gt3-forum/490448-gt3-slotted-front-rotors-deman-for-649-2-sets-available.html>

Bill Verburg

gee, here I thought that I answered it here(and other places) silly me

mark kibort

sometimes OEM manufacturers have one part number for really , directional rotors. (means one goes correctly, and the other is wrong) but on street cars, its not really an issue. (mercedes does this on the S500, or at least the OEM replacement parts companies can do this)

IcemanG17

I like the "screwdriver test"....where you drop a screwdriver in the vanes and see which direction its pointing...front brakes should be pointing to the rear of the car....

Bill Verburg

That's very difficult to believe, a single part # for the rotors at the same end of a car indicates that the internal vane structure is straight, that's the way all the 911 and normal 964 rotors are.

Bill Verburg

that works

Nugget

http://www.zeckhausen.com/how_to_pro...all_rotors.htm

Van

All Porsche rotors that have curved vanes have a left and right set.

And, believe it or not, the left one will always end in an odd # and the right one will end in an even # (the 9th digit). That's true for all left/right specific parts.

To wit: 928.351.043 - left front rotor; 928.351.044 - right rotor. 996.351.409 - left front rotor; 996.351.410 - right rotor.

p.s. I like to look at the vanes as "flinging" air out while they turn - not "scooping" air.

CWhaley

As always van you are spot on! Many people simple forget that the air is being scooped from the inside & pushed out... Why else would we be putting all that duct work in there... :-)

mark kibort

I found it tough to believe, but the guys at mercedes and SSF both confirmed it. guess they didnt think it mattered much . one part number and it was a passenger side rotor for both sides. someone screwed up somewhere down the line.

ValveFloat

Lotus Elise rotors are like that also.

mark kibort

Not all porsches! (if you consider 928s porsches ) the early 928s (pre 80) had vented rotors with no curved vains , so there were no left or right rotors, just one.

Just think of the asymetrical rotors as pinwheels or galaxies. Then, its easy to not put them on backward.