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I could have misunderstood, just been wrong, or any number of things. You say I was "snide", well what do you call your response? Yet look at the difference in how I responded, because again, it's just an opinion and nothing more. So yeah, that you have some learning to do on multiple levels seems obvious from my perspective ...
Team, whether you misunderstood or not, you made a conscious decision to belittle the person in question, rather than help them. And you kinda do that often. So, you have another decision to make: continue as you are and continue to get feedback like you get, and then justify or defend yourself, or save your energy and either stay out or, ideally, help. You obviously know a lot about these cars, and you could help many of us, but if you keep it all to yourself, nobody is really going to care who you are or what you know.
You just have to read between the lines or do your own research and people can't be bothered to do either, yet they get defensive when people don't coddle them and spoon feed them. So many delicate flowers....
I would say, "they'll learn" but that is unlikely since the average RX-8 ownership span these days is probably an average of a year.
Last edited by 9krpmrx8; Aug 30, 2017 at 05:40 PM.
My last post about it is to please stop polluting threads with your silly nonsense about me. He contacted me privately and I chose to respond here. In addition to it not involving you I help plenty, but don't expect you to be any more be knowledgable about that than anything else going on here.
Generally speaking people who ask a basic question and then proceed to try and be impressive aren't really looking for help. Unlike yourself, I don't care about being perceived as knowledgable by people who not only have no idea what it is, but then proceed to mouth off rather than either consider or listen to the good advise they asked for.
Hey looking to purchase an imported engine that has 50k miles and has been opened at some point for a rebuild i am told.(this is obvious due to sealant and painted endplates.)
however i have just had the engine tested cold at a rotary specialist.
results are as follows
Front @ 198 RPM
78 psi
73 psi
77 psi
Rear @ 202 RPM
82 psi
81 psi
84 psi
Now the technician has stated he thinks these figures should come up to the 105 range when hot...as the motor has been sitting for a while he also believes
this can contribute too a low cold result.
Just after your wisdoms on these statements and answer on the figures provided at the RPM/cold etc
Sorry to bring back an old thread but I figured I’d try and get some help with my compression numbers. I’ve used both the compression table posted in this thread with normalized readings using the foxed.ca calculator as well as another calculator from driven by madness’s yourube video and both results seem to be too good to be true. I’ve just picked up an 04 with 96k miles on first engine. Start up is slow and worse when hot, but I’ve also found there’s a 490 cca battery that’s surely contributing to slow start ups, my fuel economy is about 9-10 driving moderately and I’ve got some smoke out the tail pipes and that’s all my low compression symptoms now for compression numbers. Front rotor is 55 psi on all faces at 200rpm cranking speed at 797ft above sea level normalized to 60.41 and compression ratio of 9.4 according to what I got. Rear rotor 60 58 and 55 psi same rpm and elevation. Also Normalizes to 9.4 as much as I’d like to believe these I do not. Planning to rebuild this summer when I’ve got time hoping I can make it that long. Thanks for the help in advanced couldent start a thread as I’ve not met the posting requirements yet.
Not sure how you're calculating compression ratio, but from the factory compression ratio is 10:1. So if you're calculating effective compression of 9.4... that's a sign your engine is toast.
Try to use this: Foxed.ca - Rotary Compression Calculator
55psi normalizes to 4.66kg/cm2 which is what compression spec is measured in. 7.0 is borderline.. soo yeah, she's dead.
However, that doesn't fully explain the dismal MPG and smoke, that sounds more like poor ignition. You have some reading up to do on ignition and catalytic converter health, and common engine killers, so that when you get a rebuild, you don't make the mistake of putting a fresh engine back in without fixing the root cause.
Not sure how you're calculating compression ratio, but from the factory compression ratio is 10:1. So if you're calculating effective compression of 9.4... that's a sign your engine is toast.
Try to use this: Foxed.ca - Rotary Compression Calculator
55psi normalizes to 4.66kg/cm2 which is what compression spec is measured in. 7.0 is borderline.. soo yeah, she's dead.
However, that doesn't fully explain the dismal MPG and smoke, that sounds more like poor ignition. You have some reading up to do on ignition and catalytic converter health, and common engine killers, so that when you get a rebuild, you don't make the mistake of putting a fresh engine back in without fixing the root cause.
already has a cat delete and yes, ignition system is on the long list of parts to buy...
Im really sorry to piggyback off this thread but ive been a member for months and still cant post my own topics. Just wanted advice what you guys would pay for a otherwise perfect '09 gt with these compression numbers
I had my '05 Manual tested on Monday. adjusted for altitude and rpm both rotors came back 97 98 96. When I saw the kg/cm2, (not sure if these are adjusted or not) they came back
6.8 7.1 7.2 for the front and
6.7 6.8 6.9 for the rear.
The car has 99k on it with new ignition coils, wires and plugs (5k miles on them)
I replaced the battery and went with a higher CCA than what was recommended. Can't recall how much higher right now but if this is a factor I can update this post later.
Since the test was done I have changed the starter to the upgraded faster one and my slow hot starts have disappeared.
My question now is, could the slower starter have skewed my compression test results? Should I have it re-tested?
well if you don’t know if they’re adjusted or not it means they’re useless
it’s adjusted based on the rpm, so you get a different number based on what rpm the starter is turning, but then that’s the point of adjusting them to a common reference number; usually 250 rpm is the standard
excuse me why I go have a moment of facepalm silence ...
I had my '05 Manual tested on Monday. adjusted for altitude and rpm both rotors came back 97 98 96. When I saw the kg/cm2, (not sure if these are adjusted or not) they came back
6.8 7.1 7.2 for the front and
6.7 6.8 6.9 for the rear.
The car has 99k on it with new ignition coils, wires and plugs (5k miles on them)
I replaced the battery and went with a higher CCA than what was recommended. Can't recall how much higher right now but if this is a factor I can update this post later.
Since the test was done I have changed the starter to the upgraded faster one and my slow hot starts have disappeared.
My question now is, could the slower starter have skewed my compression test results? Should I have it re-tested?
Rotary builds up compression as they spin faster so yes, the cranking RPM would have an effect on the compression number.
That said, having a faster starter is just delaying the inevitable if your engine is worn down. As Team said, it will "improve" your unadjusted readings, but once it's adjusted to the 250 RPM sea-level standard, it will give you the same numbers as it would give you when you adjust the numbers with the slower starter.
well if you don’t know if they’re adjusted or not it means they’re useless
it’s adjusted based on the rpm, so you get a different number based on what rpm the starter is turning, but then that’s the point of adjusting them to a common reference number; usually 250 rpm is the standard
excuse me why I go have a moment of facepalm silence ...
The PSI numbers are adjusted.
I was unsure if the kg/cm2 numbers I saw on the tester were adjusted.
I appreciate the explanation of what the adjustment of numbers is and does but the facepalm comment was uncalled for. Replies like this are the reason people don't like asking questions and therefore never learn.
Originally Posted by UnknownJinX
Rotary builds up compression as they spin faster so yes, the cranking RPM would have an effect on the compression number.
That said, having a faster starter is just delaying the inevitable if your engine is worn down. As Team said, it will "improve" your unadjusted readings, but once it's adjusted to the 250 RPM sea-level standard, it will give you the same numbers as it would give you when you adjust the numbers with the slower starter.
Thank you for the clarification. I figured that would be the case. I don't really want to have another motor grenade on me, I had an old 540i that had a timing chain guide failure last year and thanks to the zero tolerance of that motor, it's dead.
Just trying to decide how I want to proceed, save for a rebuild or another car for now.
Thank you again.
Last edited by jonj; May 16, 2020 at 07:29 PM.
Reason: Add quote
Yes, it was called for as your thin skin does so readily testify. You have more to learn than you think. The question is are you teachable? Based on the last part of the reply it would suggest not. Further, people who are afraid to ask aren’t worth teaching. It it’s not that it would not be learned from not asking, it would not be learned due to a lack of effort. Because you can go find and read that numerous places on here and the internet in general to learn it.
try to be less sensitive and you *will* learn a lot more and sooner too. Feel free to ask me directly even unless you’re too afraid to learn 😱
Since this topics is up I would open a question:
Is the compression number is linearly proportional with RPM ?
All we got is Mazda service manual with a graph, later others made excel file, app, online calculator and.... base on that graph.
Problem is when the starting speed exceed 300rpm like my case which I have easy 333rpm every day of week and healthy 350rpm on fully charged battery.
I drew two additional lines after 300rpm to end of 350rpm, Red line is copy past slop from original lines and Green line is predicted from actual lines,
as you can see divergence is huge number of 1.0 kPa.
Is there any official compress graph for above 300rpm ?
There is no official guideline after 300RPM, it could be same slope of a curve in Red or more logically continuation of slope in Green.
Your red line doesn't follow from the original line. Put a straight line on it, you'll see you've created an inflection.
I don't know for certain, but it's probably safe to go with the green line, if it's computed from the known trend. I wouldn't expect the behavior to meaningfully change in 50 rpm.
Linear would be crazy, our engines don't make 48 kg/cm2 of compression at 10,000 rpm
Hey gwilliams6, I've mazda rx8 kuro 2007 since 2010 my mechanic just done the compression test and the result is front rotor 5.0 rear rotor is 4.0. sometimes the car starts a bit later then normal even engine is hot or cold.But the performance is still okay. Now my mechanic told me that just buy a Low Compression Rebuilt Kit which includes ;
Apex Seals x 6
Apex seal spring short x 6
Apex seal spring long x 6
Rotor Oil seal set
Rear Stationary Gear O ring
Outer water seal x 4
Inner water seal x 4
Eccentric shaft oil seal front x 1
Eccentric shaft oil seal rear x 1
Set of through bolt seals
Set of dowel "O" rings
Free Mazda RX-8 Engine rebuild workshop manual
What do you think guys will it be enough for repair or do I need to buy housing or any other parts to reach the pick performance?
Thanks a lot
Hey gwilliams6, I've mazda rx8 kuro 2007 since 2010 my mechanic just done the compression test and the result is front rotor 5.0 rear rotor is 4.0. sometimes the car starts a bit later then normal even engine is hot or cold.But the performance is still okay. Now my mechanic told me that just buy a Low Compression Rebuilt Kit which includes ;
Apex Seals x 6
Apex seal spring short x 6
Apex seal spring long x 6
Rotor Oil seal set
Rear Stationary Gear O ring
Outer water seal x 4
Inner water seal x 4
Eccentric shaft oil seal front x 1
Eccentric shaft oil seal rear x 1
Set of through bolt seals
Set of dowel "O" rings
Free Mazda RX-8 Engine rebuild workshop manual
What do you think guys will it be enough for repair or do I need to buy housing or any other parts to reach the pick performance?
Thanks a lot
Never go back to this mechanic again. Find a proper rotary specialist and/or order a ready rebuilt engine from a reliable rotary shop. Shadetree rebuilds replacing just the seals are only good if you enjoy doing them annually.
A proper compression test gives 6 numbers, not 2, and the rpm at which the test was done. Also with 4 and 5 compression you would have severe trouble starting the car, so I wouldn't put a lot of faith in the test results. What prompted you to test it?
RX8 Cold Compression Numbers 6 PORT
