Anything above 15 inches may require closer attention to wrist pin oiling (pin oilers) and cylinder wall lubrication. Conventional wisdom says that 12-to-14 inches of vacuum is required to generate beneficial power gains. While the rotating assembly is largely credited with creating windage in the crankcase, we must also remember that with pressure in the crankcase, rapidly descending pistons tend to pump wind toward the rotating assembly, exacerbating windage and parasitic drag. Engine builders still debate the amount of vacuum required to neutralize crankcase pressure with optimal effect on windage and ring seal, while still minimizing combustion chamber contamination. The size and speed of the evacuation pump, along with the size of the vacuum line, control the amount of vacuum.

This pressure is readable with a vacuum gauge. Improved power via reduced mixture contaminationĪn external vacuum pump evacuates excessive crankcase pressure, resulting in less-than-atmospheric pressure in the sump.Improved bay to bay breathing in Y-block configurations.Minimized cavitation (in wet sump applications).Reduced windage around the rotating assembly.Reduced friction by allowing lighter tension rings.Improved ring seal by relieving crankcase pressure below the rings.Pulling vacuum with a dedicated pump has been the preferred method for well over two decades now and the technology has steadily advanced with important performance benefits that include: Although purely passive, the system proved remarkably efficient, and thousands of racers used them religiously until the emergence of modern external vacuum pumps. This action relieves blow-by pressure under the rings, reducing windage and contamination. Exiting exhaust gasses pull a vacuum on the tubes, thus drawing excess crankcase pressure from the sump and discharging it out the collector. Traco-powered Penske Trans Am Camaros were among the first cars to run it in competition.Ī Pan-Evac system connects the valve covers on both sides of the engine to the exhaust header collectors with one-way check valves and vent tubes that blend into the exhaust stream at approximately 45 degrees. The concept was first introduced by Bill Million at Hedman Hedders and initially developed on the engine dynos at both Edelbrock and Traco Engineering. Crankcase pressure is evacuated via the valve cover and pumped to an external tank which vents the pressure and retains excess oil for periodic draining. This Reher-Morrison big-block Chevy illustrates the simplicity of an external vacuum pump system.

Delco vacuum pump in big cam 350