Hello All,

New owner here of a 2010 Manual GT with ~28K miles on it.

I recently purchased the car from Carmax and took it immediately to Mazda for a basic inspection and compression test. Here are my results:

Rotor 1: 9.1, 10.1, 9.6 kgf/cm2 at 363 RPM
Rotor 2: 9, 8.8, 8.8 kgf/cm2 at 334 RPM

After looking at the compression table I believe I saw on the guide for beginners, these results actually fall out of range of that table.

Can anyone help me interpret these results? Were the readings performed simply at too high of a RPM and worthless?

Would appreciate any input and crossing my fingers the engine is healthy, otherwise good thing for the 5 day return policy.

 

Holy hell.

That is an incredible starter speed! The highest I've seen posted on here, so yes, it's out of range of the chart

The link right above the chart is to the calculator that I used to build the chart: Foxed.ca - Rotary Compression Calculator

your numbers are then:
Rotor1: 7.38, 8.19, 7.79
Rotor2: 7.72, 7.54, 7.54
@ 250rpm, at sea level.

If you are higher than sea level, then the numbers get even better.

It's a pretty good engine, and an incredible starter.

The only two caviats that I have are:
1) Typically the starter speed from one rotor to the next only varies by 3-8rpm, not 29rpm. That's odd.
2) Rotor 1 has a 0.5 difference between two face pairs, and a 1.0 difference on another face pair. This is also odd. All the numbers are good, and the differences are within spec, just an oddity there.

 

I love my S2 starter. But I don't see 363RPM, Mine is like 295RPM ish.

 

I wonder if they used a charging pack or something, that was overcharged to like 15-16 volts, but fell off quick, thus the drop for rotor 2.

 

Thanks for the input!

Are the readings odd enough that I should get another compression test?

Also, I'm sure I'm being overly paranoid here, but I have 4 days left to return the car if I'm unhappy.

Would that compression scare you off and return it?

Or should I just stop worrying so much, I do believe I have quite a bit of powertrain warranty left and just drive and enjoy the car?

 

No, I wouldn't worry about it and just enjoy the good engine. That variation in the starter speeds could be something where they gave it more voltage than they should have, and the rotor face variation on rotor 1 could just be a bit of carbon on the seals unseating them slightly.

Give it a good wankle spanking that it might not have really had yet, and enjoy. You have at least 72,000 miles and 4 more years on the factory engine core warranty, so ntohing to be concerned about.

 

That is a solid engine, if they did the test with the WDS hooked up and printed out those results then they should be normalized already for altitude, etc.

 

After the first couple of cranks mine falls off to 280RPMish.

 

yeah, less than 10rpm drop is fairly common for what i see. a 29rpm drop is about as odd as the 363 original.

 

Thanks again for the input and I've read all your guides as well, great contributions. I've visited many forums and I've yet to see something that thorough and comprehensive.

So far I'm loving the car and the smoothness of the engine, very happy and hope the ownership experience stays that way.

Next plans are full fluid changes and a full ignition component change as well.

Then reading the countless threads on whether I should premix or not and the many options available!

 

I don't think you should need to premix with an S2 since it has an extra oil injector over the S1's, but that is just my $.02. I went through 1/2qt in my first 2 tanks of fuel so far (on tank 3 right now). Definately enjoy it, I have a nice windy road on the way home from work I take, wow does this thing love the curves. It seems to drive even better around them the faster you go. Fortunately on the way I get to some HWY driving to open her up when merging so I get the best of both worlds on my short drive to and from work!