Igneous Rock is formed when a magma cools underground and crystallizes or when it erupts unto the surface of the ground, cools and crystallizes. Magma that erupts onto the surface is called lava. When magma cools slowly underground the crystals are large enough to see.
Readings for compression tests usually vary between 175 to 250 PSI (Pounds per Square Inch). A higher reading generally indicates better engine performance; however you should check your vehicle manual to find out what the ideal reading should be for your vehicle.
Leak Down Test by Dennis Haynes. A number of people have asked What is a LEAK DOWN test? and Can I do it myself?. First, let me explain the concept. We already use a compression test to determine an engines condiditon. the problem with this test is that there are too many variables.