Can experts chime in on this compression testing procedure?
 

I am particularly interested on what your thoughts are about the psi values specified in parts 8 and 9.



Compression test using a piston engine tester:

1. note battery strength. A weak battery will yield low compression results.

2. Remove both lower plugs and wires.

3. remove EGI fuse from engine fusebox.

4. have a friend floor the accelerator pedal, opening the throttle for more airflow

5. insert your tester into the leading hole

6. hold the valve on the side of the tester open

7. have your friend crank the car over for 5+ seconds.

8. observe the needle bounces. You should see 3 in succession without skips, even bounces, in roughly the 30-35psi range.

9. let out on the valve now, and let the tester reach an overall compression value for all 3 faces(highest of 3 will be displayed). 115+ is like new, 100-115 is healthy, 90-100 is getting weak(1 year or less in most cases) below 90 could blow at any moment.

10. repeat for opposite rotor. Note difference in overall compression between rotors, which should be no more than 20psi max.

what about them? i prefer to remove the schraeder valve from the hose to the plug ports and eliminate holding the release button which gives more accurate pulse PSI readings compared to the less accurate method listed here.

you cannot get a static peak reading by removing the valve though, but that figure also doesn't mean much anyways if you have a seal bypassing pressure which is less likely to be noticed when reading pulse values peaking at 30-35psi.

best bet is to do it both ways, with and without the schraeder valve to get a good feel for peak values and how well each chamber is reacting.

Care to explain this one?
You know that the RX8 has an EGI Comp1, EGI Comp2, and EGI INJ fuse?
Only the fuel pump fuse should be removed (for obvious reasons) and the ESS disconnected (to disable the ignition coils/plugs).

Though to be honest... I've done many compression tests by simply removing the ignition wires from all the plugs and making sure they aren't near something they could "ground" to.
That way I don't have to disconnect the ESS... lazier way, but its worked for me every time.

Also, how do you plan on obtaining the RPM during the test so you can "normalize" the results?
On my car I've seen a huge difference between my weaker starter (166prm) and my upgraded one (248rpm).

they can get the rpm from some sort of reader connected to the OBDII port.

I don't need to do that ... *hugs my Mazda compression tester*

I know that... but he didn't mentioned this in his "list"

Me neither. :bootyshak

it's because it's a generic procedure from the RX7s.

You're right.
My post was to hint that following that procedure would cause confusion when he attempts to perform this on an RX8

your concern relates to any rotary engine, but if you can tell that the battery or starter is weak then you really don't necessarily need an expensive RPM/pressure tester similar to the OE mazda special tool.

if each rotor is at or above 100psi then you should know that the issue isn't related to the engine, if the pressures are dropping below 90 then a verfication of engine RPMs and starter system integrity should be looked into before tossing a towel in on the engine.

yes it's better to correlate pressure to a RPM figure for reference but it's not absolutely necessary, 5 years from now everyone will be doing compression tests on the renesis like they have done on the RX7's for many many years. many people already do as it gives you a good enough baseline to look for issues.

Oh boy...
Anyway, good luck with your test Nadrealista...

heh ok, don't think that nobody has ruled out bad engines with the test before with the simplified method.. and i thought some FD owners were anal.

all that being doubtful that someone has a super starting system with 500+ RPM cranking speeds. if so i'd love to hear the recipe.

I concur with your thoughts..if you have > 90 psi and nice even bounces for each rotor face you are probably fine..knowing rpms is more important when you see lower values and have bad idle accompanied with hard starting hot and cold.

I didn't remove the valve from my tester and got around 60psi for each rotor face on both rotors (with release valve open)..with release valve closed I got 100psi on first rotor and just above 90psi on second..car idle is rock solid and it starts right up hot or cold. So I think I am fine, not the best numbers but engine still got life left in it.

Here is a cheaper option to get the rpms...

http://www.harborfreight.com/digital...ter-66400.html