Compression Checking on a Small Block Miata

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Originally Posted by OUTRACE

I just did a compression check on my 93 with 104K on it.

1=182
2=191
3=163
4=190

I did the test COLD, and I dunno what difference it's gonna make.... Do you folks think the numbers would change drastically?

Now obviously, I'm a bit worried by #3, and I'm gonna guess it's a valve because the plugs look identical across the board. I never bothered to do the oil in the cylinder trick.

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Did you depress the accelerator when you tested, it made quite a difference on my car? That 163 psi reading seems off I wonder why the 19 psi difference? I'd like to see the results from a wet test to see if it is s valve or rings, that would help answer the question on why its lower.

The tests were done at WOT. Looking at the plugs, I'm assuming that the low cylinder is due to a valve not seating correctly. If the rings were that bad, I'd have some soot around the plug face.