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.
A compression test will tell a lot about the health of your engine. Photo Credit: Getty. Your car's engine compression can tell you a lot about the overall health of the engine. If your car is blowing blue smoke out of the tailpipe, or if your car is losing lots of oil, you could have a bad piston ring.