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Understanding Injection Pumps

Posted by Eric Rego on

When selecting an engine for a conversion, it is important to first understand the two basic types of injection pump governors and why one style of governor is preferred for repowers over the other. The two types of governors most commonly found on used B Series engines are isochronous and automotive.

Automotive governors, as the name implies, are typically used for on-road vehicle applications. This style of governor relies on the operator to modulate the fuel rate being delivered to the engine as the means to maintain engine speed under varying load. Imagine driving a car and encountering a hill. To maintain ground speed, the driver needs to increase the throttle position. By increasing throttle position, fueling is increased, which produces the increased crankshaft torque output needed to maintain vehicle speed. If an ag tractor were to be equipped with an automotive governor, the operator would constantly have to adjust the throttle every time the load on the drawbar or PTO changed. The only points where an automotive governor is capable of managing fueling rate on its own is at idle and high idle. At all other points of operation, user input is required to control the amount of fuel being delivered to the engine.

Isochronous governors, on the other hand, allow the operator to set a desired engine speed, and the governor automatically modulates fueling to ensure engine speed is maintained at the desired set point regardless of load. Isochronous governors are the style of governor that is most commonly found in off-road and agricultural applications.

One of the main challenges when selecting a suitable engine for an Oliver/White conversion is finding one with an isochronous governor. What complicates the search is the fact there are a plethora of low cost on-road engines which have been removed from pickups, buses, and medium duty trucks. When starting with an on-road engine, fuel injection pump work will be required to change the governor to an isochronous type. For B Series engines equipped with the Bosch model VE rotary injection pump, governors can typically be converted by a competent injection shop for a few hundred dollars provided no additional pump work is required.

Bosch model P7100 inline pumps are much more of a challenge, and most injection pump shops generally will recommend a complete pump exchange due to costs associated with a governor swap.

Occasionally, questions are posed regarding switching between an inline and rotary injection pump for cost or performance reasons. It should be noted that swapping between inline and rotary injection pumps require changing components within the front gear drive and the injection system (lines, brackets, injectors).

Due to the large number of injection pump variants installed on B Series engines over the years, it is difficult to discuss all the “what if” scenarios within the scope of this article, therefore we recommend reviewing the particulars of your situation with a reputable injection pump shop to determine the course of best action to meet your specific goals.


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