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!

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.

Those are good numbers, but without the rpm, its not a complete result.

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!

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.

Well I'll see what happens when I call them and ask about it.

Thanks for the replies.

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?

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.

Well that's good to hear. Got one done cause I have three weeks remaining on my engine warranty.

bump

What are you bumping for? The last thing was waiting on you. Did you have some info to bump the thread it with?

Just going to steal your post quickly :wiggle:
 

My Rx8 is putting out really similar compression numbers to this - but...
Its still being a prick to start. I have a voltage drop of about 6 volts from the battery to the ignition.. This isn't normal.. is it!?
Cheers

Nope, not normal at all. I would suspect a dying / old battery.

I edited the first post, to ask about compression numbers the dealership gave me.

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.

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

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.

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"?



That price seems reasonable to me assuming the rest of the stuff all checks out. Body damage, interior damage, etc...

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..

The trunk has one tiny dent on the back but hopefully I can just get another trunk later on.
Thanks

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.

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

Run away as fast as you can.


https://cimg0.ibsrv.net/gimg/www.rx8...4d5f9b00dc.png

Recent compression test