Chris's new build of an MX5 based car

[CTWV50]

So I'm in the process of attaching lots of little bits of rubber and plastic to my car in a most unenthusiastic way. Not enjoying this bit at all.


Decided to do a compression test on the engine. Probably out of pure boredom but it's good to know where you stand with an engine before you put it back on the road after 5+ years without any regular miles.



Happy with that. Couldn't get my head round the high numbers as 9.0 CR x 14.7 is around 130 odd psi

bit of digging.....

Compression Tests

1.6 Miata has a compression ratio of 9.4 to 1. So 14.7 psi times 9.4 equals 138 psi. But the Shop Manual lists 192 psi due to heat raise from dynamic compression. Cam timing also affects the pressure reached on the gauge. The longer duration the cam, the less the pressure.

From 1992 Mazda workshop manual (1.6L).
Compression ratio: 9.4:1 (manual), 9.0:1 (auto).
Compression pressure for both;
Standard; 192 psi,
Minimum; 135 psi,
Maximum difference between each cylinder; 28 psi.

From 1995 Mazda workshop manual (1.8L)
Compression ratio; 9.0:1 (manual and auto)
Compression pressure;
Standard; 182 psi,
Minimum; 128 psi,
Maximum difference between each cylinder; 28 psi.

in Mk2 1.8 209 is standard, 146 is minimum, max difference between cylinders 28 PSI.

Explains a lot....