> Hi Paul,
     > I'm enjoying following along with your current threads!!
     > Hope you don't mind me chiming in here again to ask another newbie
     > question:
     >
     > I've been slowly acquiring S5 NT (9.7 : 1) rotors for my 20B NA
    project
     > (much cheaper that RX8 rotors).  I had 2, and just received the
    3rd one
     > today.  I've been trying to be careful to make sure I get rotors with
     > matching weight code stamps, but the one I got today is
    different.  Can
     > you help here?  I hope you don't mind me including pictures!!  I
    tried
     > to make the files small.  The first 2 pics are the rotors I
    already had,
     > and they show a "C" along side another weird symbol (kinda looks
    like
     > a 7).
     >
     > The next pic is the rotor I got today.  It shows a "C" along side an
     > "E" :
     > My question is.......Is it OK to use all these rotors together?  Are
     > these all S5 (9.7 : 1) rotors?  Is this last rotor a weight code
    "C" or
     > "E" ?  What's the other symbol of Letter mean?
     >
     > Thanks again for all your help and knowledge!!
     > Don
     >
     > From what I gather you can't mix and match weight codes.
     > I think you need to have it balanced by an experienced
     > rotary engine balancer. The rotors must be balanced
     > about their center point and matched with all the other rotors
     > for weight and then the counter weights adjusted
     > for the exact weight of the rotors. There is a guy here in
     > So Cal that does it.
     >
     > Rotor weight codes.
     > The only thing I can find is this.
     > http://www.rx7club.com/showthread.php?p=1309602#post1309602-
     >
     > I'll forward this to Jim Mederer. Hopefully he will have time
     > to help as he gets the really hard questions :)
     >
     > Paul Lamar ...No rotor no motor.


    Hi Don;

    These all appear to "C" weight rotors.  For a 2-rotor, letter codes must
    be adjacent,
    e.g. B/C, D/E, C/D are OK  (A/C, B/D are NOT)
    The rotors themselves are balanced about their centers at the factory.
    I am not sure what the balance requirements are for a 3-rotor.
    I believe the backwards "E" and other characters are Japanese - don't
    know what they mean.
    Theoretically, the S5 rotors weigh the same as the 20B rotors, and you
    "should"?
    be able to use the 20B front and rear counterweight without rebalancing.

    I posted some rotor/balance info a few weeks ago.
    The S5 rotor faces are machined, the S4 have a rough cast appearance.
    You could also measure the depth of the combustion area.
    See attached file
    -> might be worth adding to the website.   I don't have any turbo stuff.
    A couple of housing comparisons might be useful as well, I'll see what I
    can scare up...

    When mixing and matching parts for higher than stock rpm, a custom
    balance is not a bad idea.

    Cheers
    Cary


Thanks Cary,
This is what I have:

All are machined faces.
Thanks,
Don

Hi Don;
The S5 NA rotors are at a bit of a premium for racing and higher activities :)
Worth a quick depth check on the rotor recesses to ensure they are all the same.
Personally, I would run the stock 9.0? 20b rotors in NA mode for the 5-8% HP loss.
If you have the room under the cowl - you could re-add a turbo later.
Just curious, what is your project?
(Sorry if I've missed it, I don't read all the emails)

Cheers
Cary

Hi Don;
Also meant to ask if you have removed and replaced the stock 20B exhaust
sleeve inserts.
I have heard they are quite restrictive and many people replace them
with 13b turbo inserts.
Although removing them is a good way to break taps...
Cheers
Cary



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