I had my compression tested a year ago before I bought the 84 GSL-SE I now own. Mazda gave me a rating number of 7, and said the compression was in the good range. Does anyone know what Mazda's scale is and how it relates to actual compression, or is it just as simple as saying it's 7 to 1? That would be pretty low if 7 meant 7 to 1 wouldn't it?

 

As I remember 8Kg is what they are supposed to be at full compression. Although, I have seen guys post slightly higher numbers. Mazda states 6Kg as being the lower threshold. Also, important is the variance between the three readings on each rotor. I believe that 1.5Kg's is the max variance.
hanman

 

SO a rating of 7 means 7Kg? Do you know how that relates to a ration like 9:1 for example?

 

the compression number you get from measuring the air compressed by the engines rotors has NOTHING to do with an engines compression ratio. (well, it does not for what you are asking)

The engines compression ratio is the ratio of the volume of air at the filling of the combustion chamber, to the volume of the combustion chamber at the point of combustion. in other words, how much the motor squishes the air/fuel mix down before it ignites the stuff

in a rotary this is controlled by the shape of the rotor. this lists compression ratio numbers.... http://www.atkinsrotary.com/enginepart.htm
...for your info.