2009 R3 - Compression Test Results - RX8Club.com



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Old 12-03-2017, 11:31 AM   #1
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2009 R3 - Compression Test Results

Haven't been around here for awhile, figured I'd share my latest compression results. Car has 85k miles on it now.

The results: may be time for a new motor in my baby. The dealership said it failed the test but I don't think the weekend guys know how to interpret the results. They are gonna get back to me Monday after talking to MNAO and the regular guys. Luckily they gave me photos of the raw numbers straight off the tester so I was able to normalize them using the foxed.ca calculator. By my interpretation they are still good but just barely. Here's the raw numbers:

Rotor 1: 7.3, 7.3, 7.5 x100 kPa @ 279 RPM.
Rotor 2: 7.4, 7.8, 7.7 x100 kPa @ 280 RPM.

Dealership elevation is roughly 1130 ft based off google maps.

The dealership also gave me the printout from the computer. They entered the numbers directly with no normalization for altitude (I believe the computer does that for them). But they definitely screwed up by entering the x100 kPa numbers into the kgf/cm2 fields without converting them. I'm gonna see if they figure that out on their own.

Either way, by my interpretation compression is getting low even if it is barely passing. If they are gonna give me a new motor I might as well take it. My warranty expires Dec 18th so I gotta decide quick.

I'll add results from my previous compression tests later (30k and 60k miles) if anyone is interested in how it trended.
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Old 12-03-2017, 02:59 PM   #2
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It would definitely be interesting to see the compression numbers, being that I am sitting at around 50k miles rn.

What do you use your 8 for? AutoX, DD or tracking?
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Old 12-04-2017, 12:18 AM   #3
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DD mostly. My commute is 20 miles mostly freeway. I used to do 3-4 HPDE events a year the first few years I had it but haven't done any since 2012. Man that makes me sad to say. I suspect that has something to do with the loss of compression. Imo these cars need to be driven hard to keep them healthy. I redline it once a day at least but I don't think that helps as much as a good track day.
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Old 12-04-2017, 11:05 AM   #4
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I redline it once a day at least but I don't think that helps as much as a good track day.
And realize there’s a happy medium between redlining once a day and the stresses on the rest of the car on the track: simply redline it frequently.

Last edited by New Yorker; 12-04-2017 at 11:07 AM.
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Old 12-04-2017, 04:57 PM   #5
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subbed for results as well... I would definitely take advantage of that free motor while you can.

I love my RX-8 to death - one of the best cars I have ever driven, and it is so cheap compared to many of them... but the thought of the cost of replacing/rebuilding my RE in 10-30k miles from now gives me serious anxiety. It has pretty healthy compression as of its last test in June of this year, so I hope my heavily spirited driving and good TLC helps retain that for awhile... I partially wish I went for an S2 still in warranty - but I really like how the S1 looks...
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Old 12-04-2017, 06:42 PM   #6
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Typically, if they did the test right (they usually don't in my experience as I have seen them do it cold, etc) the factory tester is hooked up USB to the WDS and the computer processes the numbers and gives you the final results. But that only really matters if you engine is borderline, if it's really low it won't make much of a difference how they do it.

It's so disappointing that these engines fail with such low mileage. I guess the lubrication system changes and others weren't enough.

Last edited by 9krpmrx8; 12-04-2017 at 06:48 PM.
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Old 12-04-2017, 08:22 PM   #7
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I don't want to push us too far off subject, but I see quite a few built, NA 13B's from the RX7 making good power, Whats the life span like in comparison, would it be worth swapping over and building as a halfway point between NA 3 Rotor or Turbo 13B? drive alot, I so I need an engine that will hold up to lots of 75% throttle time, and lots of highway miles.... 150-200k miles would be ideal...

This has pushed me to consider dare i say it....an LS Swap... but I really don't care about the power, I honestly hate LS Swaps in anything, but it makes the most sense, and they have kits that make it easy.... I'd much rather keep a Rotary in the car though.

Last edited by blackmount; 12-04-2017 at 08:26 PM.
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Old 12-04-2017, 09:11 PM   #8
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Originally Posted by Mr.ThunderMakeR View Post
Haven't been around here for awhile, figured I'd share my latest compression results. Car has 85k miles on it now.

The results: may be time for a new motor in my baby. The dealership said it failed the test but I don't think the weekend guys know how to interpret the results. They are gonna get back to me Monday after talking to MNAO and the regular guys. Luckily they gave me photos of the raw numbers straight off the tester so I was able to normalize them using the foxed.ca calculator. By my interpretation they are still good but just barely. Here's the raw numbers:

Rotor 1: 7.3, 7.3, 7.5 x100 kPa @ 279 RPM.
Rotor 2: 7.4, 7.8, 7.7 x100 kPa @ 280 RPM.

Dealership elevation is roughly 1130 ft based off google maps.

The dealership also gave me the printout from the computer. They entered the numbers directly with no normalization for altitude (I believe the computer does that for them). But they definitely screwed up by entering the x100 kPa numbers into the kgf/cm2 fields without converting them. I'm gonna see if they figure that out on their own.

Either way, by my interpretation compression is getting low even if it is barely passing. If they are gonna give me a new motor I might as well take it. My warranty expires Dec 18th so I gotta decide quick.
That engine is passing any way you slice it. Do you have any actual driveability symptoms? Don't hold your breath for a "free" re-man engine from Mazda. I would expect MNAO to decline based on the fact that it meets the minimum specification. "Free" engine are never free - there's always extra costs to consider and considerable variability in the quality of the re-man engine you could receive. If it's not giving you problems, just enjoy driving it with its Japan assembled, never taken out of the car engine.
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Old 12-05-2017, 12:02 AM   #9
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That engine is passing any way you slice it. Do you have any actual driveability symptoms? Don't hold your breath for a "free" re-man engine from Mazda. I would expect MNAO to decline based on the fact that it meets the minimum specification. "Free" engine are never free - there's always extra costs to consider and considerable variability in the quality of the re-man engine you could receive. If it's not giving you problems, just enjoy driving it with its Japan assembled, never taken out of the car engine.
This is exactly what I was thinking. Those numbers are not that bad at all. If you are not noticing anything while driving I wouldn't open pandoras box.
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Old 12-05-2017, 08:24 AM   #10
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Yeah I'm still on the fence on whether to get the new motor or not. No noticeable change in driveability. I plotted the compression test results over the years, the decline has been gradual, probably too gradual to be noticeable. On the other hand, as much as I love the car, I do want to upgrade within the next year or two and I feel it might be easier to sell it with a new motor. But then I've heard all the horror stories about the re-mans so that is a little worrying.

I'll try to get my previous test results uploaded as well as the plot I made. I left all the stuff at work yesterday.
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Old 12-05-2017, 08:52 AM   #11
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On the other hand, as much as I love the car, I do want to upgrade within the next year or two and I feel it might be easier to sell it with a new motor. But then I've heard all the horror stories about the re-mans so that is a little worrying.
Take the re-man. The recent re-mans have been looking very good.
My engine, with under 25k on it, failed the compression test, though it started/drove great. I suspect it was just carbon'd up, as the original owner was a Canadian snowbird and this was his Florida car. But we'll never know.
Like you, I was really wary of the re-man. I went ahead & had it done. It now has stellar compression numbers 10k miles later (I posted it on here somewhere).
Biggest variable is the dealer. Try to do the homework, ensure the dealer mechanic knows what he is doing. I was lucky enough my local dealership has done a zillion RX8 engines and the mechanical work was impeccable.
When you are ready to sell in a few years, the 'new' reman (and compression test) will be a selling point for the car.

good luck
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Old 12-05-2017, 08:55 AM   #12
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I don't want to push us too far off subject, but I see quite a few built, NA 13B's from the RX7 making good power, Whats the life span like in comparison, would it be worth swapping over and building as a halfway point between NA 3 Rotor or Turbo 13B?
yes but the swap is....... complex.
I loved the 190whp Rotary Resurrection-built engine in my 1990GTUs; and it'll run forever on 87 octane getting 25mpg on the highway no less. But the RX7, cherry as it was, was a crappy old rattletrap compared to the RX8.
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Old 12-05-2017, 08:59 AM   #13
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Run it into the ground while saving up $10k for an LS swap.
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Old 12-05-2017, 02:16 PM   #14
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Run it into the ground while saving up $10k for an LS swap.
Well, if OP keeps the car, then it makes sense.

If OP wants to sell it, that's a different story. LS RX-8s seem to sell for peanuts in general. At best, they sell for as much as a stock RX-8.
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Old 12-05-2017, 03:52 PM   #15
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No RX-8 is worth doing anything to unless you plan on saving it.

Really, this could be expanded to 99% of cars.
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Old 12-05-2017, 08:39 PM   #16
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Ok as promised, here are all the numbers (data and plotted) from previous compression tests throughout the life of the car. Sorry for the delay.



The number below the date is mileage.


No more LS swaps for me. I just did one in my 91 Wrangle. Don't want to do another project like that again any time soon. At this point I'm leaning towards getting the reman. It may be barely passing now but based on the trend it will be failing in another year or so. Might as well get the new motor if they're gonna give it to me free
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Old 12-06-2017, 11:53 AM   #17
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^^ Cool. really flattened out at 63k miles.
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Old 12-06-2017, 02:19 PM   #18
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Nice professional level presentation to show how the motor has aged. Thank you for that

Shame we can't get a direct representation to correlate power loss with it... My compression numbers are close to your 50K miles ones, and the car runs great, Cold and Warm starts with minimal cranking, drives, and pulls very healthy - It still is quick enough to inspire one to be irresponsible.
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Old 12-06-2017, 02:28 PM   #19
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Nice chart.
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Old 12-06-2017, 05:04 PM   #20
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Wow ... that's really interesting information !
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Old 12-06-2017, 10:06 PM   #21
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Thanks for the responses. I do a lot of data processing in my line of work so charts are kind of my thing haha. One thing I realized after posting though: there is no way to correlate the rotor chambers from one test to the the next. In other words, rotor 1 - chamber 1 on one test could be rotor 1 - chamber 2 or chamber 3 on the next test. Actually, I'm not even sure the rotor # is consistent from one test to the next. It would probably make more sense to plot the averages.
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