Mazda Rx7 13B Rotary Compression Test using standard gauges - Damaged Seal
This video was taken by my my young son using an iPad to help me assess the possible damage to my 13B.
It is not a professional production so apologies for the lack of glitz, flare, intro, outro, adds or anything else.
The video is far from a best practices guide but rather a very basic illustration of how one can easily get a rough idea of the health of their engine with very few tools.
Recording the compression throughout the life of the vehicle may prove useful in picking up on a problem before significant damage / catastrophic failure occurs.

I used two cheap (the cheapest) compression test gauges with the return valve removed.
The gauges were swapped to confirm reading consistency (not shown in video).
I selected the white gauge for the bad rotor simply for ease of reading on the video.

The video is shown at normal speed then zoomed in at 1/16th speed to catch the peak readings and overall time.

From the peaks on the white gauge the approximate (say 5psi) readings were:
Right - Rear Rotor - 85, 55, 45 psi
From a similar video I used the white gauge for the front rotor as the other gauge is a little difficult to read in the posted video and appears to indicate 80-90 psi on all 3 chambers:
Front Rotor - 75, 75, 70 psi

Adjusting for RPM, I've done the following:
1. The video was slowed by a factor of 16 (1/16th)
2. The video length for 6 compression peaks of the rear rotor was about 26 seconds (1.6 seconds at normal speed).
3. RPM = 60 * Total Peaks * Video Speed Reduction Ratio / Total Time (seconds)
= 60 * 6 * 16 / 26
= 221 RPM.
Ref: 3 peaks = one full rotation of the rotor and 3 rotations of the eccentric shaft. One peak per revolution.

Thanks to the spreadsheet from https://www.rx8club.com/series-i-do-...3/#post3158348
adjusted compression at 250 RPM is as follows:
Left - Front Rotor - 84, 79, 79 psi or 581, 548, 548 kPa
Left - Rear Rotor - 94, 64, 54 psi or 651, 444, 375 kPa

From this the rear rotor most likely has damage to an apex seal as 2 chambers are low and one is OK.
The front rotor has lost a little compression across the board.
Symptons: Hard to start, running rich, unstable boost under heavy load.
Pluses: After taking a few cranks to start, it does idle fine at 1000rpm, cruises fine, still has a little power (3psi boost using stock exhaust) and still fun to drive.

As an aside, the eccentric shaft rotates once (360degrees) to produce one third of a cycle for the 3 chambers, or rather rotates 3 times (1080degrees) to achieve one full revolution of the rotor.
A 4 stroke piston engine's crank shaft rotates twice (720 degrees) for a complete cycle, once for the compression stroke and once for the exhaust stroke.
An individual 13B rotor chamber has a displacement of just under 650cc so a full cycle where all rotor chambers have performed work is thus 650 * 3 * 2 = 3900cc. Yes there are 6 separate chambers, so one might say hey that's 3.9 Litre 6 cylinder!
Yes the engine is commonly rated at 2.6Litres capacity.
At 3.9L the rotary is running at 9000RPM compared to a 4 stroke V6 running at 6000RPM also 3.9L.
But at the same RPM, the rotary only achieves 4 of the 6 compression cycles being 4 x 650cc or 2.6L.
Get the rotary to rev more and it behaves more like a 3.9L engine that a 2.6L.