"Why are  you thinking of running the RX8 rotors for?
 The compression?
 The  bevel?

 The reason for considering the RX-8 rotors was to increase the
 compression
 ratio to 10:1 and the RX-8 rotors are lighter.  I have a set of 9.7:1
 rotors that I was considering using because they were cheap, but I
 want to
 confirm what I have before putting them in.  Unfortunately, I lost the
 info
 that I used to have to told how to tell all the various rotors apart.

 Don


 Here are some old messages Don.
 Paul Lamar

 Old messages:
 ==================================================================
 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


Hi Don;

I'm doing my part and recycling old emails ;)
Here's an old pic identifying s4 and s5 rotors.

HP difference is 3-5% approaching the torque peak. I have seen similar
numbers for piston engines elsewhere.
See the bible,  p.49:
  http://foxed.ca/rx7manual/manuals/REbyKenichiYamamoto-1981.pdf

Personally, I would keep your 20B rotors - everything is already factory
balanced.  The extra HP is a just a throttle blip higher if you really
want it.
If you really need the HP you could put a turbo back on.
I still don't know the 20B balance criteria.  You could weigh/balance
everything and enlighten the rest of us ;)

Cheers
Cary

I have the formula.

Here is some more info.

Paul Lamar

It's my understanding that you would normally replace the rotors in the same
position that they came from. I did mark mine F, C and R for that purpose.
Are there ever any exceptions to this when reusing the rotors that came with
the engine? My rotor weights with new rotor bearings are below. Given my
weights, any reason not to just put them back where they came from?

Front 4368 grams
Center 4373 grams
Rear 4355 grams

Jay

They are matched to the counter weights so it is essential.
I am surprised there is that much difference.

Paul Lamar