I was just on the phone with a mazda dealer and he said 5 and up is a good reading for a compression test as long as all the numbers are close?? Is that true or is 5 a little low?
Thanks

 

There's a worskhop manual that clearly states the numbers and a search function here that clearly shows them too.
However... 680kpa@250rpm is the min. acceptable.

 

 

the engine is designed around 9:1? ish...might be 9.1:1 but whatever, so a 5 is nearly half the ideal operating compression.

 

5 should be passing on both rotors.

 

Should be high 6's at 250RPM or highe

5 would be a fail at the normal RPM

 

per the graph chart above, 5 would only pass the minimum acceptable (Line B in the graph) if the engine RPM for the test was 175 or less ...

 

You don't know what you are talking about.

Neither do you. You shouldn't be allowed to post in technical threads.
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In addition to what Team and Dan said, you also need to correct the charted results for altitude. That chart (from the updated FSM) assumes sea-level as the reference.

I realize that I am going to get barked at about how the compression checkers are relative measuring devices and should measure pressure as a reference to local pressure, not absolute, but you find that compression results are tied to altitude.
If I wasn't feeling so foggy, I might bother with an explanation, but it was a long day.

 

I appreciate the help. So as I under stand it, it should be 250 rpm to get an accurate reading? If elevation has anything to do with it, elevation here is 4500...
Since I am new to the forum, I apologize for duplicate questions. I have searched compression etc ,but havent had much luck. Is there a place on the forum that shows graphs and more technical info on the engine so I wont have to bother everyone? :0)

 

mscamp02 and monchie ... wtf ...

Factory and some 3rd party compression tester have a "flip" switch and will convert the numbers automatically for you.

5 might pass but it depends on what rpm you did the test on. but either way, it still means your engine is going south.

As for elevation level, 4500 is pretty high so your numbers might get a little lower. There is a formula to convert it back to sea level but I just don't remember it now.

 

Ambient pressure at 4500 feet is about 85% that at sea level. So an engine at the minimum 6.8 at 250 rpm at sea level would be about 5.8 at 4500 feet.

5 still does not cut it.

Ken

 

the test rpm may vary based on the battery voltage and starter condition etc.

you will need the both the RPM readings and the compression numbers, plus the elevation compensation per MMs post, to make a proper determination