IT Rotary Engines

[Ron Earp]

I was looking through the GCR, specifically the ITCS ITS section, and noted that there is no hard data on the RX7 13B motor with respect to critical power producing specifications – mainly port sizes. Piston engines listed in the ITCS have the majority of the key specifications listed and, for the most part, some of them can be fairly accurately checked at the track with a micrometer or even a good measuring rule. Valve diameter along with bore/stroke are easily checked and with a few more simple tools the compression ratio can be measured. But with a GCR in hand there are no specifications on a rotary engine that can be evaluated.

In the paddock I have heard it rumored that there is no definite port size on the 13B rotary engine and thus a specification in the ITCS cannot be listed. I might certainly believe that some castings have a more desirable specification but then the dimensions of this particular port should be stated since it would be the maximum size. As it stands there is no way to inspect a 13B at the track unless you have a factory casting from Mazda. And even then there would be suspicion cast upon the bearer of the factory part that might nullify an inspection result.

If it is indeed true that there is no factory specified port sizes on the rotary engines then we’ve got a problem as the cars won't have confining specifications on a critical aspect of the motor.

If there is a factory specified port size it would seem to me that we might want to get some port size dimensions put into the GCR in the form of text, or if some sort of irregular shape, an engineering drawing of the port(s).