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Compression test results

Old 05-02-2012, 11:57 PM
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Compression test results

Found another 2004 RX8 and did a compression test, here are the results:

rotor 1 - 7.5 7.6 7.3
rotor 2 - 7.7 7.3 7.6

Rpm is 250

Mileage is 83,453

Let me know what you guys think. Thanks!

Last edited by ShadowDragon78; 08-05-2015 at 05:46 PM.
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Old 05-03-2012, 01:58 AM
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without the RPM of the motor at the time of the compression test the values are mostly meaningless.

If we assume the Mazda Service guy gave you the normalized values then yes ... those are quite good.
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Old 05-04-2012, 12:47 AM
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Those are good numbers, but without the rpm, its not a complete result.
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Old 05-04-2012, 10:57 AM
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I wasn't informed of the RPM it was done at, nor is it written down on the invoice I recieved....
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Old 05-04-2012, 11:22 AM
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Originally Posted by ShadowDragon78 View Post
I wasn't informed of the RPM it was done at, nor is it written down on the invoice I recieved....
Well hopefully those are the normalized values.

I looks like they provided you with most of the correct information, meaning they gave you 6 compression values.

Those are really good results, and you have no reason to believe the dealer has not do the test correctly so ... be happy!
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Old 05-04-2012, 02:44 PM
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I wouldn't say those are really good results. The differences between the rotors is pretty high and lets face it, without knowing exactly what RPM these tests were done at, they mean nothing. You can hope those values are normalized but that defeats the purpose of the test. Make them retest you for free and make sure you know exactly what what RPM they were done at (250rpm). Sometimes even the pros make mistakes.
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Old 05-05-2012, 11:25 PM
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Well I'll see what happens when I call them and ask about it.

Thanks for the replies.
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Old 05-09-2012, 12:42 PM
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They tested my #1 rotor at 283rpm, 8.4, 8.2, 8.2 and my #2 rotor 277rpm 8.8, 8.4, 8.4.

I know it says it should be done at 250rpm. So basically what I'm asking is if they did my test correct, or should i go back and get them to do it again?
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Old 05-09-2012, 01:17 PM
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No, they can't change the starter speed. There is a chart to normalize the numbers "as if" it was done at 250rpm. The original guy didn't have the speed at all, so it could be unnormalized and really high RPM, in which case his engine isn't as good as if the RPM was normal or even low RPM crank speed.

You got all the numbers, they did it fine. Just use the normalization chart to adjust the numbers down to 250RPM.
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Old 05-09-2012, 01:49 PM
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Well that's good to hear. Got one done cause I have three weeks remaining on my engine warranty.
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Old 08-05-2015, 05:15 PM
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bump
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Old 08-05-2015, 05:17 PM
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What are you bumping for? The last thing was waiting on you. Did you have some info to bump the thread it with?
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Old 08-05-2015, 05:42 PM
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Just going to steal your post quickly :wiggle:

My Rx8 is putting out really similar compression numbers to this - but...
Its still being a ***** to start. I have a voltage drop of about 6 volts from the battery to the ignition.. This isn't normal.. is it!?
Cheers
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Old 08-05-2015, 05:43 PM
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Nope, not normal at all. I would suspect a dying / old battery.
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Old 08-05-2015, 05:44 PM
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Originally Posted by RIWWP View Post
What are you bumping for? The last thing was waiting on you. Did you have some info to bump the thread it with?
I edited the first post, to ask about compression numbers the dealership gave me.
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Old 08-05-2015, 05:51 PM
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Ah, you should mention that

Good numbers for that age, assuming original engine. May not be original engine. I don't particularly like the 7.3s personally, but for the right price I wouldn't balk on not buying it. The 7.6 7.7s are good.
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Old 08-05-2015, 05:55 PM
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At the battery its still 12 volts when i try to start?
Just gets lost on the way to the key - still a sign of a dying a battery? sorry new to all of this
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Old 08-05-2015, 05:58 PM
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Originally Posted by RIWWP View Post
Ah, you should mention that

Good numbers for that age, assuming original engine. May not be original engine. I don't particularly like the 7.3s personally, but for the right price I wouldn't balk on not buying it. The 7.6 7.7s are good.
According to the dealership it is the original engine. The price is $6491, just need a few opinions on it to decide if I should buy or not.
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Old 08-05-2015, 06:02 PM
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Originally Posted by millsy100 View Post
At the battery its still 12 volts when i try to start?
Just gets lost on the way to the key - still a sign of a dying a battery? sorry new to all of this
Good compression numbers and hard starting will typically be one of:
- Battery dying
- Starter dying (though your compression test should have had the starter speed to rule this in or out)
- Ignition failing (spark plugs, plug wires AND coils all need to be changed every 20,000 - 30,000 miles, ~$200 in parts if you do it yourself, really easy)

I was just guessing a battery problem since you mentioned a voltage issue. How are you measuring voltage "at the key"?



Originally Posted by ShadowDragon78 View Post
According to the dealership it is the original engine. The price is $6491, just need a few opinions on it to decide if I should buy or not.
That price seems reasonable to me assuming the rest of the stuff all checks out. Body damage, interior damage, etc...
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Old 08-05-2015, 06:05 PM
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Might go back and ask for the starter results - he didn't tell me those!

Just taking out the bottom of the dash and getting in behind and measuring with a voltage meter - it sits at 12 volts if i only have the electrics on but as soon as i try to fire it drops to around 6.
Have just replaced all coils leads plugs etc.
So i guess thats only really leaving me starter or battery..
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Old 08-05-2015, 06:06 PM
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The trunk has one tiny dent on the back but hopefully I can just get another trunk later on.
Thanks

Last edited by ShadowDragon78; 08-05-2015 at 06:09 PM.
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Old 08-05-2015, 06:37 PM
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If you didn't get the starter speed with your compression scores, you have no idea if compression is a problem or is fine

For example those numbers ShadowDragon posted are stellar at 200rpm, failing at 300rpm. The RPM of the test is REALLY important. It's ok if they normalized the numbers to 250rpm and gave those to you, but that obviously won't tell you your starter speed.
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Old 08-02-2016, 04:50 PM
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About to buy, lemon or no lemon?

I had the dealership do a compression test on a 2007 rx8 touring. It has 92,000 miles on it. The original motor was replaced at 13,000 miles. So the newer engine has 79,000 miles on it. This is high from what I have read. Here is the compression info I received, I don't know if these are normalized yet. Elevation is 614'. I realize these fail if not normalized, even then they are borderline. Any other opinions? I just really want an rx8, fell in love with it on the test drive.
R1
6.1
6.3
6.1
214 RPM
R2
6.1
6.6
6.2
224 RPM
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Old 08-02-2016, 05:38 PM
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Run away as fast as you can.


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Old 12-21-2018, 02:53 PM
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Recent compression test

Hi guys

Had a compression test on a 2006 RX8 I'm considering buying, some advice if these results are good or not please

@ 250 rpm
No. 1 No.2
compen
695.37. 670.37
674.37. 631.37
623.37. 774.37

Thanks


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