Rochester Ramjet

Rochester Ramjet system installed on a 1957 Chevrolet 210

TheRochester Ramjetis an automotivefuel injectionsystem developed by theRochester Products DivisionofGeneral Motorsand first offered as a high-performance option on theCorvetteand GM passenger cars in 1957. It was discontinued partway through 1965 in favor of the ChevroletBig Blockas a performance option.Unlike electronic fuel injection systems that would become common decades later, the Ramjet is purely mechanical and relies on vacuum and pressure signals to measure airflow and meter fuel.

History

Rochester Ramject as seen on 1959 Chevrolet Passenger car.

In the early 1950s, fuel injection was the topic of a significant amount of research by theauto industry in the USand internationally.Ed Cole,who had become the chief engineer of Chevrolet in 1952, pushed for Chevrolet to be the first GM brand to offer a fuel injection option on aproduction car.Much of the development of the Ramjet was done by engineer John Dolza, with supporting effort fromZora Arkus-Duntov.Dynamometer-based tests of a 265 cidsmall blockengine running with fuel injection were performed as early as 1955.

Between 1957 and 1965, the Ramjet was offered as the top performance option on the Corvette. When it was first introduced, it passed the threshold of one horsepower per cubic inch ofengine displacement,and this fact was used in marketing material.In addition to the Corvette, the system was offered on Chevrolet and Pontiac passenger cars; each of which used a slightly different configuration with respect to the air cleaner and other components. Within the Chevrolet brand in 1957, Ramjet was covered byRPO-578 on the passenger cars and RPO-579 on the Corvette.

Although offered on Corvettes until 1965, the Ramjet system was available on Chevy passenger cars from 1957 through 1959.

Technical details

The Ramjet is a continuous-flow port-injection system. Unlike later fuel injection systems that used electronics, this one is based on purely mechanical principles. The two main sub-assemblies of the system are theair meterand thefuel meter.The air meter measures airflow into the engine and manages thermostatic warmup enrichment, fuel shutoff on overrun, and idle settings. These measurements are sent via pressure and vacuum signals to the fuel meter, which contains the high-pressurefuel pumpand controls delivery of fuel to the injector nozzles.

There are three easily identifiable revisions of the Ramjet, each spanning three years of the system's nine year production life. The first of these (1957-1959) are identified by the "finned top" sand cast plenum, followed by the "flat top" plenum (1960-1962), and finally the die-cast plenum (1963-1965). All versions of the system required a specialdistributorthat provided a cable drive to the high-pressure fuel pump.

Limitations and issues

Although the Ramjet system allowed a significant increase in engine performance, its innovative design had several inherent issues that affected reliability andtuning.On the early systems (1957 through 1961), one of these problems affected the cold-start fuel enrichment: it would tend to discretely toggle on or off, rather than using a gradual series of steps. Later systems used electricchokesor exhaust-heat chokes for cold enrichment, although these had issues of their own. Additionally, thevapor pressureof modern pump gasoline may not be appropriate to preventpercolationin the Ramjet fuel distribution spider.

The cranking signal valve was also the source of reliability issues. It was intended to pass a certain maximum vacuum signal that would be used for fueling during cranking (i.e. before engine start). The valve would sometimes fail in a partially open position and cause the fueling to run much richer thanstoichiometric.