View Poll Results: What was your psi?
Voters: 30. You may not vote on this poll
What's Your Compression?
01-15-2003, 12:18 AM
#3
Senior Member
Join Date: Apr 2002
Location: IL
Posts: 2,930
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.
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.
01-15-2003, 12:28 AM
#7
Senior Member
Join Date: Apr 2002
Location: IL
Posts: 2,930
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 ?
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.
01-15-2003, 12:36 AM
#8
Super Moderator
Join Date: Jul 2001
Location: NJ
Posts: 17,839
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.
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.
01-15-2003, 01:30 AM
#10
Junior Member
Join Date: Dec 2002
Location: Chicago, IL
Posts: 14
According to my 1988 Rx-7 FSM,
Compression vs. Cranking Speed compensation chart (67U01X-023)
Compression vs. Altitude compensation chart (67U01X-024)
See the links/URLs for the larger size charts
/Seva
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)
Compression vs. Altitude compensation chart (67U01X-024)
See the links/URLs for the larger size charts
/Seva
