Ok, I know a lot of people (including myself) have been looking for compression numbers. Well, I just happened to find in some spec books from Mazda, the proper compression numbers. Heres what it says:

Displacement:
12A Engine - 573 CC (35.0 cu-in) x 2 Rotors
13B Engine - 654 CC (40.0 cu-in) x 2 Rotors
Compression Ratio: 9.4:1
Compression Pressure Limit: 600 kpa (85 lb/in2) at 250 RPM
Max permissible Difference Between Chambers: 150 kpa (21lb/in2)

So there you go boys and girls, take it as you wish, but thats the numbers Mazda threw out there.

~T.J.

 

Sadly those numbers won't work for and engine that cranks at 300RPM

 

How does one know what their cranking RPM is? If it cranks at a higher RPM, wouldn't that mean that compression is lower?

Just curious.

 

The Mazda compression tester will have a display showing what the engine RPM is/was at the time of the reading.
The higher the RPM, the more the seals are pushed to the rotor walls, kinda why a rotary has such low compression at low RPM and the need for the E-Brake as the motor can still spin over while parked on a slight incline in gear

 

Well, thats what it said . I just thought Id pass it along incase anyone wanted to know...Just thought Id be nice .

~T.J.

 

here is what mine came out to a month or so ago around 104k on her.
Front 7.3/7.5/7.3 - 341 RPM
Rear 7.5/7.7/7.9 - 348 RPM