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I.D. Guide: The Rochester Roster

Little Did Zora Duntov Know That Fuel Injection Would Be Used Exclusively In Every Car Produced By Gm 30 Years Later

Andy Bolig Nov 1, 2000

Step By Step

This is a model number 7014520 fuel-injection unit. It replaced the preceding 7014360 unit in the ´57 production year around vehicle serial number E57S102900.

Differences between the two are identified in the cast top of the 4520 unit with "snowflake" Winters Foundry mark at the front of the plenum (shown), while the 4360 units have the snowflake in the top center of the plenum. The tube connected to the front of the plenum also identifies this unit as a 4520.

All ´57 and early ´59 units had sand-cast meter boxes which were fastened by only a bottom-bolted brace as compared to the other units which used a top bracket also.

This is a 7014800 unit. It's the third revision of the fuel-injection unit for the ´57 model year taking place around serial number E57S105000. You'll notice the absence of the foundry mark on the top and the piping from the front of the plenum, and the inclusion of the extended line to the power diaphragm from the fuel-richening housing around the front of the unit.

Two key points to help you date the ´58 fuel-injection unit (7014900) would be that it was the first year to use a cranking signal valve and it was the last year that did not use a distributor bushing as shown in the photo. There were two settings for the 4900 units--7014900 and 7014900R, the "R" units having been set 6-8 percent richer for use on mechanical lifter, 290hp engines.

Another distinguishing factor for the ´58 unit is that the power diaphragm line goes under the plenum chamber. Also, the reconditioned ´58 models had external siphon breakers installed which kept fuel from siphoning into the cylinders when the engine was shut off. You’ll notice a 2-1/2x3-1/4-inch brass block that looks like a spacer between the gear pump and the fuel meter connected to a return line that goes up between the plenum and fuel meter. Later ´59 units (7017200 and 7017250) were the first to have integral siphon breakers. Also, ´59 was the first year for the removable bushing for the distributor.

The ´59 unit (7017300) is actually a reworked ´58 unit and can be distinguished by the "L" fitting on top of the fuel meter...

...and the electric starting solenoid under the fuel meter.

The ´60 and ´61 unit (7017320) can be distinguished from the earlier-style units by the flat top of the plenum.

Also, the crank signal valve is located on the side of the plenum.

The ´62 unit (7017360) has the choke moved from the top... the side of the housing and this is the only year for the crank signal valve to be located in the center of the power valve on the fuel meter. Airflow was increased from 580 to 680 cfm to accommodate the new 327/360hp engine.

The ´63 units were an obvious change from the earlier units. This is a 7017375 unit. You can see by this photo that the choke is now heat-operated and the cranking signal valve is lower on the power valve (not centered).

The ´63 unit (7017375) is the first fuel-injection unit to use a PCV valve, located at the right rear of the plenum chamber.

The ´64 and ´65 model years both used model number 7017380 which was a revised 7017375 unit. The most distinguishable feature for the "7380" units is that they use a front-mounted PCV which connects to the oil fill tube.

The 7017380 units did not use a cranking signal valve, but instead had a solenoid that was wired into the engine harness. The reason was that the solenoid operated only when the starter was engaged and was not sensitive to vacuum changes.

Another change on the 7017380 unit was that the distributor vacuum line was removed from the air meter and the port was plugged. The line was moved to the rear of the plenum chamber where the PCV had been for the prior model (7017375).

Today’s Corvettes perform to a level of reliability and performance that can only come through years of experience. The fact that they can satisfy our appetite for performance while also fulfilling the requirements for emissions and fuel economy proves the benefits of using fuel injection over the conventional carburetor.

Little did John Dolza, who is credited with developing GM fuel injection to a practical point, and Zora Duntov, who helped refine the system in preparation for the ´57 production year, know that fuel injection would be used exclusively in every car produced by GM 30 years later.

The first fuel-injection units were designed with only performance gains in mind. Overcoming the fuel starvation problems experienced with carburetors during hard cornering was the primary objective of designers, and history reveals that they did their job well. We asked fuel-injection specialist Jack Podell to show us what differences to look for when identifying the Rochester Mechanical Fuel Injection units.

This listing is by no means comprehensive of every change or model unit that GM had instituted over the course of production, but is intended to give the reader a good foundation of the Rochester Mechanical Fuel Injection units that started it all.


Jack Podell
South Bend, IN 46617

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