According to Mazda, your results should read between 6.9kgf and 8.5kgf at 250rpm. Cranking speed and compression are directly related. Mazda state that any rotary engine needs 180rpm to start. I've found this to not be completely true but it is a good indicator, so anything faster than 180rpm is good, you really need 230rpm - 250rpm.
Just to be clear, in the same way that a slow starter motor won't start a healthy engine, a very fast starter motor (i.e. 280 + rpm) will start an unhealthy engine and so can be used to mask engine problems. If, after you've had a compression test carried out, you find that your starter motor is slow but your engine is healthy, simply fit a faster starter motor or fresh battery. I have seen this scenario work on several occasions so it does occasionally happen!
Unfortunately in 80% + of cases it is low compression that is the problem, not helped by a particulaly slow starter motor on the older cars.
In this instance you have two options:
- You can gamble and fit a fast starter motor and new battery to mask the main issue in hopes that it will start or
- You can opt to have your engine stripped down and rebuilt with new parts giving it a new lease of life.
The first option, a new starter on a dying engine, I don't particulaly think is a fix. It will buy you some time if you are not ready for the expense of an engine rebuild, but ultimately the engine problems will progress to the point where it simply fails. Mazda does however think that it is a fix until you are out of warrantee see "BAND AID ON BROKEN ARM".
Quite frankly it is likely that during failure damage will occurred to the major engine components meaning that the rebuild will be far more costly than it may otherwise have been, when starting first became hard.