Compression Results good or bad
Hello again! Was curious on compression results
Car is 86 NA 5 speed 90 87 85 Alt 91 88 86 267 rpm Rear Rotor^ Front Rotor 92 98 90 267 rom 90 96 88 alt Rotary Tester was used are these any good or slightly off and tired?! I know the Haynes manual says 85 is minimum but some people say 80- 90 is normal for NA S4s due to compression ratio. Also this is my second rotary not knowledge enough just yet but I know all the faces should be even the more the better. |
My first question would be was the engine at normal operating temperature when the compression test was done? If not, it should be for the most accurate results.
To me, those numbers are borderline, but I feel as though the engine would run just fine but you could expect a slight dip in power and to get slightly lower fuel mileage. Are you experiencing any hot start issues? |
Originally Posted by spurs fan2
(Post 12535828)
Hello again! Was curious on compression results
Car is 86 NA 5 speed 90 87 85 Alt 91 88 86 267 rpm Rear Rotor^ Front Rotor 92 98 90 267 rom 90 96 88 alt Rotary Tester was used are these any good or slightly off and tired?! I know the Haynes manual says 85 is minimum but some people say 80- 90 is normal for NA S4s due to compression ratio. Also this is my second rotary not knowledge enough just yet but I know all the faces should be even the more the better. Also, when you tested, I'm assuming you tested per Mazda's procedure - i.e., engine at operating temps, throttle wide open? Both will effect test results |
Originally Posted by Pete_89T2
(Post 12535860)
With those numbers the motor is getting a bit tired, but it still should be a good runner - it should start hot or cold and make decent power when running. If it's NOT doing that, your problem is not compression.
Also, when you tested, I'm assuming you tested per Mazda's procedure - i.e., engine at operating temps, throttle wide open? Both will effect test results |
Originally Posted by mazdaverx713b
(Post 12535859)
My first question would be was the engine at normal operating temperature when the compression test was done? If not, it should be for the most accurate results.
To me, those numbers are borderline, but I feel as though the engine would run just fine but you could expect a slight dip in power and to get slightly lower fuel mileage. Are you experiencing any hot start issues? Also no issues with hot starts to notice so far have had it about a month |
I would do it again with my own rotary compression tester just so I know it was done correctly. However, if it's running that well and the mileage is that low, I honestly wouldn't worry about it too much. It sounds like the engine is stil pretty solid and the car has likely been well maintained!
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