its pretty easy.



67-72 cosmo: 6mm apex seals, double side seals, 3 rotor oil control rings per side, its a 10a so very narrow



68-74 10a: same as the cosmo, but with 2 oil control rings like everything after that



70-73 12a: wider than 10a rotors by 10mm, 6mm apex seals, double side seals.



74-76? (might be 78) 12a: 3mm apex seals, single side seals



78-82 12a: has leading deep recess for faster burn (tear drop shape), can be ided by a single f or r stamp in the combustion recess, rotors are different front and rear



83-85 12a rotors: these are lighter and had compression bumped to 9.4 from 9.2 (i think), and can be spotted by an N R or N F stamp in the combustion recess. they are not swappable front and rear



83-85 12a turbo: lower compression, never seen one so i dunno if there are any marks



74-85 13b: only 13b rotor with 3mm seals, and the big 1mm side seals, 12lbs cast combustion recess



86-88 non turbo: 2mm apex seals, .06mm side seals, lighter than the earler rotors, they are about 10.5lbs, still cast combustion recess



86-88 turbo: same as na except deeper recess, due to the lower compression, 8.5:1



89-91 non turbo: lightened more, to about 9.5lbs, these have a machined combustion recess, and compression is 9.7:1



89-02 turbo: machined combustion recess, deeper than the na. compression is now 9.0:1. the fc and fd rotors have different part numbers but they have no visual differences *the rotor bearings are different*



03+: theres are yet still lighter (8.5lbs), have a shallower apex seal groove, edges of rotor face are cut at an angle (mitered?) for better flow

 

is there a good way to mesure the depth of the combustion pan? Just looking at them may prove difficult

 

i used a tape measure and got 1/4" for 86-88 na and 1/2" for 86-88 turbo but your mileage may vary

 

One might be able to get a really rough estimate of the combustion recess by doing some measuring and figuring.



You could also take the rotor in question to a machine shop to have them pour into it. This would give you the volume of the combustion recess but then again you would have to have something to compare the rotors in question against.



I vote for looking at the letters if possible. :]

 

the letters and numbers are so you can sort the seals into the factory seal case

 

The S4 is the cast face. The S5 and FD are both machined faces... and indentical by sight. The only difference that is easily discernible between S5 TII rotors and FD rotors are the rotor beraings.

 

i cleaned this thread up and made a couple of revisions/additions to the list.

 

I wanted to start a thread here (hopefully a sticky if it warrants it and gets enough technical information) to display the different types and series of rotors and show their visual characteristics for identification purposes. This has bugged me for quite awhile so I've taken a bunch of pictures of two different series' turbo rotors (S4 and S5) in search of markings and differences between the two that would be easily spotted. I figure it'd be a handy thing to have around to verify different things.



I've always been puzzled when it came to why there's a "front rotor" as well as a "rear" even though they have the same weight, compression, etc. Perhaps this thread will help that.



Any and all info would be greatly appreciated. I'm doing this for both myself as well as the group's knowledge to hopefully provide a better resource than word-of-mouth on this subject.



B

 

First, I want to go over weight codes. On each rotor, there's a weight code stamped on the gear side near a Japanese symbol. This weight code is not listed on the oil jacket side of the rotor. Below are two pictures (one of a series 5 turbo and one of a series 4 turbo thereafter) that show their respective weight codes:











As you can see, the S5 Turbo rotor has a weight code of 'D' and the S4 Turbo rotor has a weight code of 'B'. There are 5 weight codes: A, B, C, D, E that will be stamped on every single rotor. The weight code of 'A' represents the heaviest;

'E' the lightest. When mix and matching rotors, the weight code must be looked at closely: A pair of rotors may only deviate by as much one weight code (either heavier or lighter) during assembly. A 'C' rotor, for example, may be paired with a 'B' or 'D' weight, but an 'E' may not be paired with an 'A', 'B', or 'C'.

 

Secondly, I want to display one visual difference between the S4 and S5/FD/Cosmo rotors:



The S4 and older rotors seem to have a cast "bathtub" compression face, where as the S5 and newer are all machined. The S4's is rough with casting 'bumps' (on right) where the S5's is smooth with vertical 'lines' (on left):







B