- back pressure
-  The resistance to the flow of exhaust gases through the exhaust system. By rerouting the exhaust gases for noise suppression, a muffler causes back pressure, but a straight pipe alone causes only minimal back pressure. Some engines require back pressure, so that removing the exhaust system will cause internal damage. Pressure in low side of refrigerating systems; also called suction pressure or low-side pressureAlso see
Dictionary of automotive terms. 2015.