MECHANICAL FUEL PUMP FOR MFI
Mechanical fuel injection uses a positive displacement fuel pump to load the jetting distribution system. Proper fuel pump size and jetting is vital for good performance and good spark plug readings.
In the past, Hilborn fuel pumps were rated by the manufacturer at 1,800 RPM fuel pump speed. Enderle, Kinsler, and most other fuel pumps were rated at 4,000 RPM fuel pump speed.
As a result, Hilborn pumps rated at the slower speed would appear smaller. Yet, when they were run at higher RPM, they were comparable in size to other manufacturers.
FUEL PUMP SPEED
Most installations gear or belt drive the fuel pump to 1/2 engine speed. A Hilborn fuel pump at 1,800 RPM would correlate to an engine speed of 3,600 RPM. Other fuel pumps rated at 4,000 RPM would correlate to an engine speed of 8,000 RPM. The later 4,000 / 8,000 RPM combination is commonly used as a standard by most MFI flow bench services world wide.
EXAMPLE OF BUZZING THE FUEL PUMP FOR MORE POWER
A 20 GPM fuel pump for nostalgia nitro racing would be at an engine speed of 8,000 RPM. Many of the competitors gear the wheel speed on these racer cars to run higher engine speeds. Over 10,000 RPM is common. The same 20 GPM fuel pump flows upward of 25 GPM at the higher RPM. Fuel mixtures for the class running over 85% nitro produce a lot more power at the higher operating RPM.
Technical: About 50% of the combustion is stoichiometric. About 50% is monopropellant. As engine speed is increased, the monopropellant portion of combustion increases, and power goes up.
REFERENCE: Fuel Injection Racing Secrets, Blown Nitro Racing on a Budget.
LATEST NEWS: REALLY HIGH PRESSURE
One of our friends is currently developing a very high pressure fuel pump for MFI using an industrial design. The purpose is greater atomization such as what occurs in high pressure gasoline direct injection as well as diesels for highway use. We will update as more info is produced.