In the late Fifties, the performance wars were going full blast. GM’s Rochester Products Division and Chevrolet had made tremendous advances in carburetion. The Rochester carburetor provided amazing flexibility and dependability through the entire range of operation in high compression engines. However, there were a number of factors that limited the efficiency of the carbureted fuel system. Primarily, the problem was compromises to the fuel/air mixture problems due to limited manifold design equality. The manifold size was limited due to operation range requirements and the necessity for a "hot spot" in engine warm-up. Because of lower front cowl height, the carburetor and air cleaner height had to be low to clear the hood. What the Rochester engineers concluded that low speed operation vs. high performance was a difficult problem to solve without going beyond carburetion.

01: It was all smiles at Rochester Products Division when the first 1957 production fuel injection unit was packed for shipment to a Chevrolet assembly plant.

      Their solution was fuel injection. Using fuel injection provided a better torque curve at low engine speeds, improved fuel distribution, a stable slow idle with better starting and warm-up. There were even improvements to emissions, with fewer unburned hydrocarbons during deceleration.
     Even with its benefits, fuel injection had several drawbacks, especially higher costs and poor fuel economy. Rochester engineers also found that fuel injection had poor vapor handling capacity and fuel filtration. Even more troublesome was the need for service on a constant basis to maintain peak performance.

02: This is a full detail schematic of the early Rochester fuel injection system.

     Chevrolet became actively interested in the GM fuel injection system, primarily for the Corvette, in order to realize the full potential of the engine for high performance. Fuel injection had been used for many years on truck and passenger car diesel engines, and Rochester had developed their version with an eye to make it available for the 1957 model year.
     Two types of fuel injection were considered and tested at the GM Tech Center and at Rochester. The "A" type, which was continuous flow injection with the nozzle located directly outside each cylinder, spraying into the intake port, and the "B" type, which was timed injection. The "A" system was developed by the Engineering staff at the GM Tech Center and the "B" by Diesel Equipment Division and the research staff. The "A" system was chosen for earliest release, primarily from a standpoint of simplicity and cost.

03: 1957 #7014360 fuel injection unit seen from driver side.

     The Rochester fuel injection system has three basic components: the air meter, the fuel meter and the intake manifold. The air meter supplies a control signal to the fuel meter in response to engine load (vacuum in the intake manifold is a measure of how much air is entering the engine). The fuel meter uses the vacuum control signal to regulate the fuel flow to the injection nozzles. The intake manifold provides the distribution system for the rammed airflow to the cylinders.
     The first Rochester fuel injection unit was #7014360. Very early units did not have the familiar black Rochester Products I.D. tag, and the unit number (serial) was stamped into the lower front of the plenum vertical face. Early plenums had the "Winters Snowflake" cast in the ribbed area of the plenum.

04: Unrestored 1957 #7014360 unit, passenger side view. Note the sand cast fuel meter and large main diaphragm cover.

     Early #7014360 units used a dual four-way fuel meter distributor or "spiders" to deliver fuel to the nozzles. Later #7014360 and subsequent units had a single right tube spider. This change took place around 2/1/57. It should be noted that the single spiders used through 1957 and 1959 #7017300 and 7017300R units have lines individually attached by ferrules and nuts. Later spiders are soldered together beginning in 1958. Also early #7014360 units had three designs changes.

09: 1957 #7014360 fuel meter stampings ##7014362 and 1523. Please note that serial number of components usually did not match the unit serial number.

     Also in 1959, two new units were released, the #7017200 and #7017250. The #7200 and #7250 are very similar to the #4900, and they may be very difficult to tell apart if the model plate is missing. Both of these units had a fuel meter design that incorporated an internal "cast in" siphon breaker to stop the possibility of the fuel flow from the reservoir into the engine cylinders. The siphon breaker can be found as a protrusion on the side of the fuel meter body closest to the intake manifold. These fuel meters were die cast, as were #4900 meters. This design was continued through 1965 with minor changes.

11: 1958 #7014900R air meter unit stamping "901" on top of mounting flange. Most air meters are stamped on rear vertical flange.

Identification Tags
     The identification tag, which includes the part number and serial number, is riveted to the left side of the manifold at the front corner. The part number is also on a triangular foil tag held by one of the screws attaching the enrichment diaphragm cover.