Compression Results good or bad
10-02-22, 06:27 PM
#1
Junior Member
Thread Starter
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.
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.
10-03-22, 05:32 AM
#2
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?
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?
10-03-22, 05:58 AM
#3
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.
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
Last edited by Pete_89T2; 10-03-22 at 06:01 AM.
10-03-22, 07:38 AM
#4
Junior Member
Thread Starter
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
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
10-03-22, 07:41 AM
#5
Junior Member
Thread Starter
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?
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
10-04-22, 05:21 AM
#6
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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