Fuel System Pressure Comparison

As vehicles have become more fuel efficient, major fuel system upgrades have been made. As the chart below shows, fuel system pressures have jumped quite a bit as engine technologies have changed.

PSI chart

Carbureted vehicles often used a mechanical fuel pump that operated at 1 or 2 pounds per square inch (PSI) of pressure. This was sufficient fuel pressure for a carburetor, as fuel jets were fairly large and the spray of fuel was "good enough" for the era.

However, when port fuel injection arrived, fuel system pressures jumped up to 40-60 PSI. These higher pressures were essential, as injectors were smaller than jets and needed more pressure to get the fuel "out" in a short time span.

As a result of this massive increase in fuel pressure, fuel pumps became electric. In addition to being more reliable than mechanical fuel pumps, electric fuel pumps were more energy efficient than a belt driven fuel pump.

As direct injection became popular - first in diesel engines, and more recently in gasoline engines - fuel system pressures have increased substantially. A port injector in a gasoline engine might operate at 40 PSI, but an injector in a "DI" engine operates at 1,500 - 4,500 PSI. These higher pressures are required to get the fuel "out" in what has become increasingly short injection pulses.

As we look to the future, new stratified direct injection engines and/or HCCI engines will likely require even higher pressures. Some engine developers say that these next generation engines will have pressures of 8,000 or 10,000 PSI.

It's incredible to think that between the mid 1980s and the mid 2020s, fuel system pressures might increase by a factor of 10,000. Fuel pumps don't get a lot of credit for the improvement of the modern automobile, but as you can see, they deserve it.