Just had my 65k FD compression tested...results?
08-02-05, 08:36 AM
#1
RX7 lover
Thread Starter
Just had my 65k FD compression tested...results?
Hi all, just had my standard 92 FD compression tested. She has around 65k on the clock i think. Results are around the 85psi mark on all faces of both rotors. Thats pretty poor, right?
08-02-05, 09:40 AM
#3
Where did you have it tested?
If you had Mazda do it with their special tool the readings will be metric not PSI
A reading of 8.5 is good in that case.
85 psi on a warm motor with a little oil in it means it is time for a rebuild.
Are you having problems with hot starts of the engine?
What propted you to get the test done.
If you had Mazda do it with their special tool the readings will be metric not PSI
A reading of 8.5 is good in that case.
85 psi on a warm motor with a little oil in it means it is time for a rebuild.
Are you having problems with hot starts of the engine?
What propted you to get the test done.
08-02-05, 09:47 AM
#4
From the FAQ:
28) What should the compression be?
Compression test results are reported as six numbers: 3 per rotor. (This is not the same as the compression ratio). Higher, more equal numbers are best. The original Mazda specs dictate 8.5+ kg/cm² as new (121+ psi), with 6.0 kg/cm² (85 psi, 690kpa) being minimum acceptable. Maximum difference should be 1.5 kg/cm² (21 psi, 150kPa) from the highest to lowest value. It is important this test is carried out using proper equipment and under the correct conditions for rpm and engine temperature. Mazda dealers are generally reliable for performing this test, so long as they follow the procedures precisely.
See also the factory service manual page C-10 to be sure the rpm and altitude were correctly adjusted. Be sure the shop compensated correctly - rpm is somtimes ignored.
In any case, the numbers are low enough to suggest it's time to save for a rebuild. The even numbers are a good sign, but at some point it might get difficult to start and lose some power.
Dave
28) What should the compression be?
Compression test results are reported as six numbers: 3 per rotor. (This is not the same as the compression ratio). Higher, more equal numbers are best. The original Mazda specs dictate 8.5+ kg/cm² as new (121+ psi), with 6.0 kg/cm² (85 psi, 690kpa) being minimum acceptable. Maximum difference should be 1.5 kg/cm² (21 psi, 150kPa) from the highest to lowest value. It is important this test is carried out using proper equipment and under the correct conditions for rpm and engine temperature. Mazda dealers are generally reliable for performing this test, so long as they follow the procedures precisely.
See also the factory service manual page C-10 to be sure the rpm and altitude were correctly adjusted. Be sure the shop compensated correctly - rpm is somtimes ignored.
In any case, the numbers are low enough to suggest it's time to save for a rebuild. The even numbers are a good sign, but at some point it might get difficult to start and lose some power.
Dave
08-02-05, 10:17 AM
#6
RX7 lover
Thread Starter
yeah, it was between 80-82psi on the back rotor at 252rpm and between 83 and 85 psi on the front at 262 rpm (so i guess the speed accounts for the difference.)
The car wasnt totally warm actually, i literally pulled into the shop and me and the guy spent around an hour doing other diagnostics before we compression tested it, although the car was up to temp when i pulled in.
It was done with official mazda equipment, by a qualified mazda mechanic, although he openly admitted he knew less about Rx7s than i did!
The car wasnt totally warm actually, i literally pulled into the shop and me and the guy spent around an hour doing other diagnostics before we compression tested it, although the car was up to temp when i pulled in.
It was done with official mazda equipment, by a qualified mazda mechanic, although he openly admitted he knew less about Rx7s than i did!
08-02-05, 10:19 AM
#7
RX7 lover
Thread Starter
Originally Posted by swilson@assetworks.com
Where did you have it tested?
If you had Mazda do it with their special tool the readings will be metric not PSI
A reading of 8.5 is good in that case.
85 psi on a warm motor with a little oil in it means it is time for a rebuild.
Are you having problems with hot starts of the engine?
What propted you to get the test done.
If you had Mazda do it with their special tool the readings will be metric not PSI
A reading of 8.5 is good in that case.
85 psi on a warm motor with a little oil in it means it is time for a rebuild.
Are you having problems with hot starts of the engine?
What propted you to get the test done.
Got the test done as part of my endless quest to spend money on this beast
nothing prompted me to do it.
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08-02-05, 10:36 AM
#8
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What has been done to your FD over it's lifetime? It's just interesting that you could pull 5.8 while I have 8.5 at similiar mileage (61k vs. 65k). Do you know of any severe problems/mod'ing that has been done to your engine over time?
Mine's seen meticulous maintenance and minimal power gains, which is probably why it's still great...
Mine's seen meticulous maintenance and minimal power gains, which is probably why it's still great...
08-02-05, 10:41 AM
#9
RX7 lover
Thread Starter
Well, i dont think its ever had anything done, it has apexi filters and thats about it afaik, although at one point it did have a full, 1 piece 4.5 inch racing exhaust on it, which leads me to believe that it might have had other mods too...i noticed today a sticky patch on the interior where it looks like a boost controller/fuel computer might have been fixed, but it did have all the original vac lines ?
The engine was also relatively cool when tested...but i wouldnt think that this would make that much difference would it?
The engine was also relatively cool when tested...but i wouldnt think that this would make that much difference would it?
08-02-05, 10:51 AM
#10
Racecar - Formula 2000
Originally Posted by BobfisH
The engine was also relatively cool when tested...but i wouldnt think that this would make that much difference would it?
08-02-05, 10:52 AM
#11
Back in the 7 life again
from what I have heard a cold engine will usually have a better test than a warm one... I guess the idea is what do you want to do with it from here?
1.) if you are going to keep it as is and just have fun then dont worry about it and drive it till it pops
2.) if you want to get into serious tuning (aftermarket turbo/s) then you might want a healthy engine from the get go
Basically you have a old motor that is showing low numbers that drives well... your choice from there...
1.) if you are going to keep it as is and just have fun then dont worry about it and drive it till it pops
2.) if you want to get into serious tuning (aftermarket turbo/s) then you might want a healthy engine from the get go
Basically you have a old motor that is showing low numbers that drives well... your choice from there...
Last edited by su_maverick; 08-02-05 at 10:55 AM.
08-02-05, 11:55 AM
#12
RX7 lover
Thread Starter
yes thats true maverick, i dont want to spit an apex seal and take out the turbos though...
although that would obviously *force* me into a t78 or similar...decisions decisions!
although that would obviously *force* me into a t78 or similar...decisions decisions!
08-02-05, 02:47 PM
#13
Back in the 7 life again
well, its not like you are risking detonation and blowing a chunk of an apex seal out... what is happening is the seals are wearing down and creating too much of a gap and that is why you are losing compression.. the only way you are going to risk detonation is by putting too much stress or improper af mix on your car... thats why I say that if you want just a fun stockish car to drive around in then you are fine but if you want to mod it then start fresh
08-02-05, 03:57 PM
#14
Originally Posted by swilson@assetworks.com
85 psi on a warm motor with a little oil in it means it is time for a rebuild.
Could someone please explain to me why everyone thinks that an engine needs a rebuild because of low compression? Not one person on this thread has mentioned anything about carbon sticking of the seals(which will in fact lower your compression). If your car is stock and only 65k, a reading in that range could easily indicate carbon problems. Search the forum for carbon cleaning. Then go back and re-test. I have 96k on my stock Fd with original engine and have higher compression numbers than 85psi. I also have a 20b that had ZERO compression when I got it. I cleaned out all the carbon build-up freeing the seals and guess what the compression came back.
Bottom line, low compression does not always mean rebuild.
Last edited by t-von; 08-02-05 at 03:59 PM.
08-02-05, 04:38 PM
#15
Back in the 7 life again
very true, there might be buildup on the seals. But we can speculate night and day about what it could and couldnt be... the one saving factor seems to be the even compression along the seals... correct me if Im wrong but isnt the acceptable variance 10% from seal to seal?
08-03-05, 02:28 PM
#20
Originally Posted by BobfisH
i will do a carbon clean on it then i guess, but as mav says - the numbers are even through the board. Its hard to believe there is that much carbon in it!
Poor fuel grade and granny driving contribute the most to carbon build-up. An excessively rich engine will really have carbon problems. Trust me, it doesn't take long for the carbon to stick the corner and side seals in their grooves. Those seals are under low spring tension and because of their location, don't move as much as the apex seals.
08-03-05, 02:40 PM
#21
Originally Posted by RX 4 Speed
Can anyone lead me to how a "carbon cleanup" is done or at least direct me to where I can find it?
https://www.rx7club.com/showthread.p...ight=ATF+water
Water works great and it's free
I do this every 6 months as routine maintenance. You can also spray some regular carburetor cleaner down the same vacuum nipples to clean out the engine. Just do a search!
08-04-05, 09:26 AM
#22
RX7 lover
Thread Starter
The fuel we have over here is 98 ron optimax, shell - and its ALWAYS been given that...its specified as the highest performance fuel on the UK market 
I do drive like a granny sometimes, whats the best way to get rid of carbon?
I do drive like a granny sometimes, whats the best way to get rid of carbon?
08-05-05, 01:17 AM
#24
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Compression Test
Hey guys, I've been trying to find some info on compression tests and came on this thread. I've been looking into buying an RX-7 and after getting the compression test done, the guy gave me 4 #'s. Isn't there suppose to be 6? He supposedly had it done at the dealer.
From what I've read this is what I should be getting in terms of results:
He said:
I'm not quite sure what I'm suppose to make of this.
Thanks for your help,
Josh
From what I've read this is what I should be getting in terms of results:
Compression test results are reported as six numbers: 3 per rotor. (This is not the same as the compression ratio). Higher, more equal numbers are best. The original Mazda specs dictate 8.5+ kg/cm² as new (121+ psi), with 6.0 kg/cm² (85 psi, 690kpa) being minimum acceptable. Maximum difference should be 1.5 kg/cm² (21 psi, 150kPa) from the highest to lowest value. It is important this test is carried out using proper equipment and under the correct conditions for rpm and engine temperature. Mazda dealers are generally reliable for performing this test, so long as they follow the procedures precisely.
No: engine only has four sparkplugs were are you geting this info.Are you sure you know what your buying? This is not a reguler car. if your just read about thing on line and getting wrong info.
#1 7.7
#2 7.7
#3 6.5
#4 5.5
#1 7.7
#2 7.7
#3 6.5
#4 5.5
Thanks for your help,
Josh
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