Here is an e-mail that Dave Lemon from Mazdatrix sent an RX-7 forum member on the subject. Just thought you guys would find it interesting:



We are using RX-8 rotors in one of our SCCA E/Production "street port" 86-91 13B non-turbo engines.

We do no mods to the rotors (except installing the racing rotor bearing).
We are using RX-8 racing ceramic apex seals (the OEM RX-8 steel seals warped too much having to cross the exhaust port).
(There IS enough metal to cut the apex seal groove for either 86-91 2mm seals or earlier 3mm seals -- we are looking into making that service available, but are not ready yet)
The rotors are run "backwards" (front in rear, rear in front) so the angle cut on the side of the rotor gives more intake opening timing (RX-8 uses the cuts for the side exhaust ports).
Do not use the "oil scraper ring" outside the second oil control ring.
DO NOT use RX-8 corner seals -- they DESTROY 86-91 side housings !!!! (use 86-91 corner seals, TRUST ME).

They ARE lighter than 89-91 non-turbo rotors, have higher compression, and are less expensive.

With all of the above said: We have YET to attain even the SAME horsepower on the dyno as we are getting from our race engine(s) using the 89-91 non-turbo rotors !!!

Potentials:
With the RX-8 rotor having the side seal further outboard, we were able to increase the (ported) intake opening timing versus the earlier rotors -- it may be too much ??? (does not seem likely)

Running the rotors with the angle cut for intake opening may also be in the above category.

We always set pre-92 side seal clearance at about .0015 (1 1/2 thou). The SMALLEST clearance we could get, using the LONGEST of the available "pre-sized" RX-8 side seals was about .010 (10 thou), with the worst on this set of rotors of about .016 (16 thou). This gives a much lower "sealing" than we like.

Other than the above, at this time we are not at all sure why the power is less than when using the earlier rotors.

No, we have not done the REAL test -- run the SAME engine on the dyno, and only swap the rotors (backwards, then normal). That equals three builds, and three full dyno on-and-offs + dyno sessions.


Dave Lemon,
Owner of Mazdatrix,
The dyno operator and driver of the E/P car