In 1913, Louis Seguin and his brother Laurent (engineers who founded the "Société Des Moteurs Gnome" Gnome motor company in 1905) introduced the new "Monosoupape" series, which eliminated the inlet valve, replacing it with piston-controlled transfer ports similar to those found in a two-stroke engine. Beginning with the power stroke, the four-stroke engine operated normally until the piston was just about to reach the bottom of its stroke (bottom dead center, or BDC), when the exhaust valve was opened "early". This let the still-hot burnt combustion gases "pop" out of the engine while the piston was still moving down, relieving exhaust pressure and preventing exhaust gases from entering the crankcase. After a small additional amount of travel, the piston uncovered 36 small ports around the base of the cylinder, leading to the crankcase which held additional fuel–air mixture (the "charge"). No transfer took place at this point since there was no pressure differential; the cylinder was still open to the air and thus at ambient pressure. The overhead valve exhausted directly into the slipstream since no exhaust manifold could be practically fitted to the spinning crankcase and cylinders. The lack of an exhaust manifold also saved weight and prevented excessive amounts of gyroscopic forces in flight.