Stock Compression for a 1983 12A motor.
 

What is the stock compression for a 1983 mazda rx7 12A?

My 80 SA 12A OE manual sez it should be 85PSI @250rpm for a new motor. FWIW.

Stu Aull
80 GS
Alaska

Not disputing what your book says, but would that be the minimum acceptable? Seems low, normally, good strong compression is 120-125psi. I normally see 10 to 15 more cranking rpms too. Depending on the condition of your starter and battery cranking rpm can vary, and the slower you spin it, the lower the psi will read.

If you use the mazda or similar rotary compression tool, you will see the numbers mentioned
above.

If you use a regular tester and are watching the bounces its very hard to tell what the actual
compression is. It only tells you if all the faces have the same compression or not really. In
you other thread I think you saw 75 on the front and 65 on the rears which is probably not
bad using a regular tester holding the button in.

I wouldn't get compression, when I held the button down, so that is why I was worried.

Some compression testing gauges work differently. Were i to hold in the release button on my Snap-on gauge it wouldn't register any compression....

You can use a piston compression tester, but it takes some experience knowing what to expect or how to correlate the reading. Without knowing the cranking RPM (one of the things a rotary compression tester gives you) it can be kind of a ballpark check.