The deactivation of one or more engine cylinders is a method that has been proposed as offering potential for vehicle fuel economy improvements. At low power output the throttle is nearly closed. This introduces a 'throttling loss', which is the energy the engine must expend to draw the fuel-air mixture through the carburetor throttle opening. By operating an engine on a reduced number of cylinders and operating these at high power levels, the throttling losses are appreciably reduced. The operating cylinders are therefore run at a high brake-mean-effective pressure (BMEP) and therefore potentially more efficiently. EPA received a request from Automotive Cylinder Deactivator System (ACDS) to perform a 511 evaluation of their cylinder deactivator. Section 511 of the Motor Vehicle Information and Cost Savings Act (15 USC 2011) requires EPA to evaluate fuel economy. Retrofit devices with regard to both emissions and fuel economy, and to publish the results in the Federal Register. Such an evaluation is based upon valid test data submitted by the manufacturer and, if required, EPA testing.

"EPA-AA-TEB-81-7." Cover title. "October 1980."