Miata Cyl 4 Compression Bad When Cold

This might be a strange question, but here goes. :) I am well aware that a compression test must be run when the engine is hot. I have a '94 Miata Chumpcar and it seemed to be a bit down on power. Last race it developed a significant exhaust leak, but it seemed down on power even prior to the problem. The engine has ~120k miles and ~30 hours on the track. As a sanity check I decided to run a compression test with the engine cold. I figured as long as the engine was consistent and I could add 25-45psi and call it a day.

Cold: 130, 125, 130, 60

Hot: 185, 178, 175, 168

I read online that the spec is: Max 182, Min 128, Max difference between cylinders 28

How could the cold compression on cyl 4 be so different? Is this an indication of a problem? Obviously even the cyl 4 hot compression leaves something to be desired.

In my experience healthy engines don't have that much difference between hot and cold compression readings.

I guess the next step would be to do a leakdown test to see where the compression is being lost. Actually, before you do the leakdown, you should drop some oil into each hole and retake the compression test. If cyl 4 goes up a lot, it probably has a ring problem.

Once you're done diagnosing compression and figure out if you will use that engine or get another, Get the injectors flowed and cleaned and test your fuel pressure to see if your fuel pump is working ok at high rpms.

What are the valve clearences?

Since the steel valves expand less than the aluminum head- it's possible that one valve is so close cold that it leaks. Which will also mean it gets worse as it warms up to get better- as the valves warm up to temp faster than the head does.

possible

Valve adjustment is a very good suggestion.