NoPistons -Mazda Rx7 & Rx8 Rotary Forum - What's Your Compression?

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NoPistons -Mazda Rx7 & Rx8 Rotary Forum (https://www.nopistons.com/)

- 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

Quote:

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

Quote:

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

Quote:

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

Quote:

Originally Posted by pengaru' date='Jan 15 2003, 01:28 AM

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

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