I'd like to ask experienced members who from their own experience or from what they have come across thru others to chime in with what they would predict to be compression numbers for a reasonably well maintained 2009 Series II RX-8 with 32,000 miles.

I'll post the numbers for a car I am considering after getting several sets of opinions as to what these are expected to be.

I'd rather do this experiment rather than first post my numbers first so they do not influence members assessment.

Feel free to give one number in kg/cm2, one number for each of two rotors, or six numbers for two rotors. PSI is OK too. All should be normalized.

 

Really depends on the price. I have an R3 with about 10,000 more miles and my compression test at the dealer last year was over 9kg/cm2.
From what I researched on the forum if you're above 8.5 you have a very healthy engine. If you want to be more meticulous getting an oil analysis done from "blackstone laboratories" may be worthwhile in addition to the compression test.
Good luck!

 

Every rotary engine is hand-assembled, so no two are exactly the same. There is no way for us to know the full driving and maintenance history of this engine and car, to know what condition it should be in. Variables such as health of ignition system components, health of cooling components,seal lubrication, carbon buildup, exhaust and cat conditions, all can contribute to good or poor health of this engine. It can even matter if the engine was broken-in properly or not at the beginning. We do know, without looking inside the engine,what test numbers reveal good or poor compression.

 

bax, from what I have read, at or over 9kg/cm2, if it has been normalized, is extraordinary, even more so if a vehicle has 42,000 miles. In my case, I would have zero expectation that the vehicle I am considering would have such a stellar reading at 250rpm.

gw, thanks for the chart. I do have that. Primarily querying here for what folks would expect in the real world for cars they have measured with similar mileage (for well or not so well-maintained cars,) or from their experience.

 

The relationship between mileage and compression is not linear, so the question doesn't have an answer. It's not like these engines have a expiry mileage. It's a 2009, so series 2, should be quite improved in terms of reliability over the older ones. I would not expect it to be near failing at all, probably around a comfortable 8-8.5. But the individual example you are looking at could be in much worse shape or much better shape, there is really no predicting that.

 

Loki. Thanks. That is true. There are many variables at work.

But none-the-less, looking for actual experiences to log for comparison. It'll be interesting to see a range.

 

stevekat I can appreciate what you are looking for. However when you say you want actual experiences "with similar mileage (for well or not so well-maintained cars,) or from their experience.", that again gives such a wide range that not many may be able to satisfy you with the comparison data you seek.

I think you are better off just knowing the compression of your own car, and going from there.

Cheers !

 

I'd pretty much like to get the range of compressions for Series II with similar mileage.

It it were a wide range it would be welcome. If that wide range came with some additional info that informed the type of upkeep or driving the car had, even more so.

We already know what compression constitutes excellent, good, fair and bad. Knowing where one's potential choice may fall in the continuum of cars out there can help in making one's choice from what's available, and/or an arrive at an appropriate valuation.

 

Mine came in at 6.7-6.9 (failing). 24k miles, 2009 R3

I suspect the p.o. super-babied the car, and a good Italian tune up might have helped it. But we'll never know, as it now has a new engine, courtesy of warranty.

 

If the car still runs - enjoy it. Ensure your coils/plug/wires are healthy, cat is not clogged, and you may get more years before a rebuild (that said the engine is under warranty).

My 2010 GT compression # were all 7.9 with one 8.0 at 31K miles when I bought the car in 2015 from a one previous owner. He had it serviced at a local Mazda dealership for everything including frequent oil changes.

Best of luck

 

Thanks wannawankel (and acroy.)

The numbers on the car I am looking at are:

Rotor 1: 8.1, 8.0, 8.0 normalized
Rotor 2: 8.0, 7.9, 8.0 normalized

This appears to be good and adequate, but not necesarily stellar. It is in line with you wannawankel, above acroy's experience. The first respondent on this thread reported 9.0's - have not seen that reported often in my reading. Unfortunately have not seen a big universe of values for SII's reported, so not sure how to evaluate other than the table or ranges on RX8Help.com. I guess I'd like to see 8.5's, but not sure how often that happens.

 

What was your cranking RPM?

 

This was done by Mazda and reported as such on the work order, so I have assumed it is normalized to 250 rpm.

 

I've got a surprisingly healthy S1, so I can't really chime in. I know the S2's were supposed to have worked some of the faults out, but rough math on mine @250 RPM using the calculator and normalizing for sea level was 9.0+ on all 3 faces for both front and rear. I don't think this car was ever babied, and that might have saved it's life, but it also had consistent if not early oil changes at 3k all it's life from what I can tell.

 

Thanks. That's excellent. Sounds like 9.0+ kg/cm2 is more common that I thought.

 

Everything worked out and I completed the acquistion of this R3. I may pick up the rotarycompressiontester.com unit and run a test myself, or have the prior test confirmed by another Mazda dealer if they have an attractive rate. The rates from Mazda seem to be all over the place.

I popped into the Mazda dealer dealer who did the test referenced above and they confirmed it was normalized to 250 rpm.