I thought this would be fun...
With my squish band hemi head that is cut to the liquid cooled DT200 specs and step cut for the copper head gasket,and my "Aggresive Desert" port job, I have 132 PSI at 4,500 feet,so the "sea level" reading will be 150 PSI.
Ive had lots of people ask me if the compression is low on they're atv,bike,etc. For example (genuine)..."Is my stock blaster's 115 psi compression low to you?. The book says that it should be more than that."
I say ..."no" ..."compensate for the altitude", then show them how.
A very simple method is to add 3.4% for every 1000ft in elevation to your compression reading.
This way,folks at higher altitudes don't freek out thinking that they need a top end rebuild. I've known people that have done this... Wasted money for no reason,because they unknowingly "thought" they're compression was low,or some know-it-all jackass told them it needed rebuilt ,because he (the jackass) says it was too low. X(
Here's another way to do it... I pulled this off the web...
When at altitude,and you want to find out what the "sea level" reading would be (used in every engine manual known to man on planet earth) just divide the number in the chart instead of multiplying it.
Please tell us what you have for PSI and altitude where your at.
Anyway here it is...a good short read,and handy to know.
Altitude and temperature also affect the compression readings. Manufacturer’s specifications are almost always given at a specific altitude (14.7 psi at sea level), and 59° Fahrenheit. Both temperature and barometric pressure change as you go up in altitude, so you will need to correct your measurements if you wish to compare it with a factory specification. The following chart provides conversion factors for correctly compensating for changes in altitude:
Compression Test Altitude Compensation Factors
Altitude Factor
500 0.987
1500 0.960
2500 0.933
3500 0.907
4500 0.880
5500 0.853
6500 0.826
7500 0.800
8500 0.773
A standard compression reading of about 150 psi at sea level in Los Angeles would measure significantly less in the surrounding mountains. For example, at an elevation of 6000 feet, the expected reading would be 150 psi X .8359 = 125 psi. The cylinders would be reading low if compared to sea level measurements, yet perfectly fine at this altitude.
With my squish band hemi head that is cut to the liquid cooled DT200 specs and step cut for the copper head gasket,and my "Aggresive Desert" port job, I have 132 PSI at 4,500 feet,so the "sea level" reading will be 150 PSI.
Ive had lots of people ask me if the compression is low on they're atv,bike,etc. For example (genuine)..."Is my stock blaster's 115 psi compression low to you?. The book says that it should be more than that."
I say ..."no" ..."compensate for the altitude", then show them how.
A very simple method is to add 3.4% for every 1000ft in elevation to your compression reading.
This way,folks at higher altitudes don't freek out thinking that they need a top end rebuild. I've known people that have done this... Wasted money for no reason,because they unknowingly "thought" they're compression was low,or some know-it-all jackass told them it needed rebuilt ,because he (the jackass) says it was too low. X(
Here's another way to do it... I pulled this off the web...
When at altitude,and you want to find out what the "sea level" reading would be (used in every engine manual known to man on planet earth) just divide the number in the chart instead of multiplying it.
Please tell us what you have for PSI and altitude where your at.
Anyway here it is...a good short read,and handy to know.
Altitude and temperature also affect the compression readings. Manufacturer’s specifications are almost always given at a specific altitude (14.7 psi at sea level), and 59° Fahrenheit. Both temperature and barometric pressure change as you go up in altitude, so you will need to correct your measurements if you wish to compare it with a factory specification. The following chart provides conversion factors for correctly compensating for changes in altitude:
Compression Test Altitude Compensation Factors
Altitude Factor
500 0.987
1500 0.960
2500 0.933
3500 0.907
4500 0.880
5500 0.853
6500 0.826
7500 0.800
8500 0.773
A standard compression reading of about 150 psi at sea level in Los Angeles would measure significantly less in the surrounding mountains. For example, at an elevation of 6000 feet, the expected reading would be 150 psi X .8359 = 125 psi. The cylinders would be reading low if compared to sea level measurements, yet perfectly fine at this altitude.
