What are the acceptable compression numbers for a 1995 Mazda RX-7 FD?

For a 1995 Mazda RX-7 FD (13B-REW engine), compression test results must be normalized to a standard cranking speed of 250 RPM and adjusted for your altitude to be considered accurate ².

Here is how to interpret your compression numbers:

Minimum Acceptable Specs

• Minimum Value: The factory service manual specifies a minimum acceptable compression of 7.0 kg/cm² (approximately 100 psi or 680 kPa) ⁶.
• Worn Engine: Readings in the 6.0 kg/cm² range indicate the engine is worn out ⁶.
• Hot Start Issues: Mazda previously used an 80 psi minimum before updating it to 100 psi; however, you typically will not experience hot start issues until compression drops below 80 psi ⁷.

Healthy Engine Specs

• A strong, healthy, or freshly rebuilt engine will typically show compression numbers between 112 psi and 125 psi (approx. 8.0 to 8.6+ kg/cm²) ².

Acceptable Variances Raw numbers are only part of the equation. You must also check the variance between your readings to ensure consistent sealing:

• Between Chambers: Maximum difference of 20 psi between the three faces on the same rotor.
• Between Rotors: Maximum difference of 20 psi between the front and rear rotors ⁸.