NoPistons -Mazda Rx7 & Rx8 Rotary Forum

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-   2nd Generation Specific (https://www.nopistons.com/2nd-generation-specific-17/)
-   -   What's Your Compression? (https://www.nopistons.com/2nd-generation-specific-17/whats-your-compression-10695/)

rotary>piston 01-14-2003 11:46 PM

I just want to know what most people get for compression.

vosko 01-15-2003 12:12 AM

my FD has 150psi ... :bigthumg:

pengaru 01-15-2003 12:18 AM

most people don't even do these compression tests correctly.



Slapping a compression gauge on a spark plug hole and just cranking the starter does not equate a valid compression test. You need to be able to confirm what RPM (with some level of precision) the motor is cranking at before your compression readings can be conclusive beyond the level of 'ok it's not a blown seal'...



many people tell me things like 'OMG you got 85PSI thats HORRIBLE?!' without even knowing what RPM the test was done at. 85PSI @ 200RPM is just fine and dandy. Just something I find annoying with people, on the other forum especially.

pengaru 01-15-2003 12:22 AM


Originally Posted by vosko' date='Jan 15 2003, 06:12 AM
my FD has 150psi ... :bigthumg:

@what rpm?

vosko 01-15-2003 12:22 AM

don't most engines rev the same speed with a fully charged battery. generally speaking ?

vosko 01-15-2003 12:23 AM


Originally Posted by pengaru' date='Jan 15 2003, 01:22 AM
@what rpm?

i don't freaking know. i was paying attention to the compression gauge not the rpms 200-250 rpm i guess ??

pengaru 01-15-2003 12:28 AM


Originally Posted by vosko' date='Jan 15 2003, 06:22 AM
don't most engines rev the same speed with a fully charged battery. generally speaking ?

simply put, NO.



there are quite a few variables, some major ones are:

state of the starter motor, old ones from 1980's cars will not crank like they did in 87.

state of the electrical connections

wether the other rotor had both spark plugs installed or was not producing compression at the time of the test (this effect RPM significantly)



you can count the spikes on the compression gauge during the test over a 15 second period and just do the math to figure out the RPM... my friends 87 T2 gave ~90psi@200rpm...



check out the shop manual, there is a compensation chart for this purpose, look up compression testing in it.

vosko 01-15-2003 12:36 AM


Originally Posted by pengaru' date='Jan 15 2003, 01:28 AM
simply put, NO.



there are quite a few variables, some major ones are:

state of the starter motor, old ones from 1980's cars will not crank like they did in 87.

state of the electrical connections

wether the other rotor had both spark plugs installed or was not producing compression at the time of the test (this effect RPM significantly)



you can count the spikes on the compression gauge during the test over a 15 second period and just do the math to figure out the RPM... my friends 87 T2 gave ~90psi@200rpm...



check out the shop manual, there is a compensation chart for this purpose, look up compression testing in it.

i didn't do it judge ito did. he knows how to do a compression test. are you angry today ? did a user piss you off ? clickety clickety ??? https://www.nopistons.com/forums/pub...#>/biggrin.png

rotary>piston 01-15-2003 12:41 AM

I got about 85 1 mile above sea level at about 250 rpm. Is that good?

seva 01-15-2003 01:30 AM

According to my 1988 Rx-7 FSM,



Code:

Compression:

  588 kPa (6.0 kg/cm^2, 85 psi) -- 250 rpm

Differential limit of chambers:

  147 kPa (1.5 kg/cm^2, 21psi) -- 250 rpm



Note:

  Compensate the compression values if they are measured at cranking speeds different then standard or if they are measured at a high altitude.





Compression vs. Cranking Speed compensation chart (67U01X-023)



http://sevatech.com/cars/rx-7/compre...-rpm-small.jpg





Compression vs. Altitude compensation chart (67U01X-024)



http://sevatech.com/cars/rx-7/compre...-alt-small.jpg



See the links/URLs for the larger size charts



/Seva

hugues 01-15-2003 07:39 AM

The compression numbers given in the FSM are for when the official MAZDA tester is used.



I am not too sure about these numbers when you use a regular compression tester (witch schrader valve out) from autozone or the likes.



hugues -

j9fd3s 01-15-2003 10:58 AM

it shouldnt matter what tester you use as long as you convert the units correctly



mike

Erik 01-15-2003 11:16 AM

over 125 psi on both in my 91 n/a



T2 tested at just over 100 on both

j9fd3s 01-15-2003 01:10 PM

the t2 should be lower because its got a lower compression ratio



mike

cymfc3s 01-15-2003 02:04 PM

dont make a huge deal over compression numbers. They can sometimes vary. its not a piston engine. if it starts and runs. Its fine.

j9fd3s 01-15-2003 03:28 PM

you mean if it idles smoothly its fine



mike

ChainSawOnSteroids 01-16-2003 07:45 PM

i have 13456433 gazzillion psi, or three whooshes

pengaru 01-16-2003 07:53 PM


Originally Posted by ChainSawOnSteroids' date='Jan 17 2003, 01:45 AM
i have 13456433 gazzillion psi, or three whooshes

was this at 8000rpm? https://www.nopistons.com/forums/pub...IR#>/smile.png

ChainSawOnSteroids 01-16-2003 07:55 PM

no ,,, that was at 27,430 rpm right before i was gonna shift mad quick yo!

hillbilly 04-12-2007 11:27 AM

first time I did a compression check on my 7 (6 months ago) I took out the leading plugs, grounded the leading coils, left the trailing plugs hooked up (wait, this gets better) screwed the ol compression tester into the L2 hole, had a rubberband holding the release valve on the tester, angled it in such a way that I could see it from the drivers seat, turned the key and the car started... no ****. ran like crap and sat at about 200rpms, but F%$# me man, it took a minute of disbelief before I shut her down again. had to buy a new compression tester though, wasnt sure if it'd still be good after that.

Leetheslacker 05-22-2007 09:20 PM

4 year old thread ftw

RotaryRocket219 05-22-2007 10:08 PM

as long as you remove both plugs F and R rotors and crank with valve removed on a full batt and good starter its purrrty accurate. ive yet to see over 110 though but then again they were on garage rebuilts with used housings so .........



party on garth

djmtsu 07-24-2007 01:05 PM

failocaust


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