Got my engine compression checked this morning, as the car hit 55K miles on the clock and I wanted to see if there were any impeding engine issues before the powertrain warranty expires at 60K.

test #1:

front rotor: 7.8 8.1 8.2 at 222 RPM
rear rotor: 7.6 7.9 8.3 at 215 RPM

test #2:

front rotor: 8.1 8.7 7.9 at 215 RPM
rear rotor: 8.4 8.2 7.8 at 235 RPM

Looks like it passed with flying colors! Those numbers seem to me at spec or above.

Original engine: 55K miles. Emissions recall performed at 25K miles. I typically redline the engine once a day, up in 7K RPMs several times a day. Running dealer's 5W20 for oil changes every 5K, Castrol GTX 5W20 for topping up.

Apparently I have the original starter, if I'm spinning at low 200 RPMs. (Never flooded the car or had a starting problem, but for some reason, I assumed I had the upgraded starter, so I never bothered trying to get it.. too late now, out of 50K warranty).

 

I wouldn't say that is "flying colors" or that it even passed.

The thing that stands out to me is one chamber is at 7.9 and another is 8.9- that's a HUGE variation between faces. Your rear rotor isn't as bad but 8.4 to 7.9 isn't good, either.

Mazda would give you a reman with numbers like that

 

55K is still under warranty. Just go to a dealer ASAP and get them replaced.

I don't know how much mine is. But the thing runs super fast so I'm not worried.
(Super fast at least for me, the rears keep slipping at times even with DSC and KUMHO SPT)

 

Dude, where do you see 8.9? Yes, it seems that one rotor is consistently a little lower than the other two, but not by much. The biggest difference in one run I see is 8.7 vs 7.9 at a 215RPM. If nothing else, it's the 8.7 number that seems to be the outlier, since the lower RPM is supposed to produce lower numbers compared to the others.

 

I'd say your fine. You have some real variance in the first test on the rear rotor, but on the second test that variance is gone... I mean, the numbers are really at odds from one test to the other which, for me, seems to idicate that a comp test is just not an end all be all for our engines. I have lower numbers than you and I'm turning at 290ish RPMs:
R1 @ 292
7.7
7.7
7.7

R2 @ 293
7.6
7.5
8.0

But, the numbers are pretty damn even from rotor face to rotor face... So, in my opinionm a vacuum test may be a more accurate indicator. Just my opinion, though.

 

Vacuum is a reflection of compression but not as accurate as a compression test. The dealers use it as a tool because it is MUCH quicker and simpler to hook a vacuum gauge to the side of the intake manifold, than it is to remove plugs and unplug the CAS and do a comp test.

Not a concern to most rx8 owners, but engine porting in a rotary can also change vacuum numbers, as can idle/throttle plate settings.

 

If those are your numbers you should take your car into Mazda for a new motor. At ~290 RPM's your numbers should be at 9 something.
Railton