Racing with Fuel Pump Inlet Restrictors

Restricted Fuel Pump Sizing with Inlet Restrictors

Certain racing classes specify fuel pump flow value limits.  The common way to achieve this is fuel pump size.  However, another way to achieve this is to restrict the fuel pump inlet using a larger fuel pump.  When this is done, it cavitates the fuel pump, limiting the output.  In Nostalgia A-fuel drag racing, this is the latest method to reach the fuel pump rating.  Previously a smaller fuel pump was used to reach the fuel pump rating.  The more recent change provides an advantage.  At lower fuel pump operating speeds, higher fuel pump volumes are achieved with the restricted larger pump than those from the previous smaller pump.  Record runs in Nostalgia A-fuel dropped from low 6 second ETs to high 5 second ETs with this change.  These engines are drunk on power from greater amounts of high percentage nitromethane fuel mixtures at the lower engine speeds even though they have essentially the same amount of fuel at the high end as before.

Fuel Pumps with Inlet Restrictors Applications

Inlet restrictors may be creeping into other classes with fuel pump size limits.  They provide the use of lower cost, standard fuel pump sizes in some cases.  They also provide interesting tuning possibilities.  It may be possible to flat line a fuel curve for a normally (naturally) aspirated engine with an inlet restrictor.  Essentially the fuel pump cavitates when it reaches a specific flow value.  Fuel flow numbers are limited as engine speed increases.  This feature could be matched to the fuel curve of a normally aspirated engine where the amount of fuel beyond the torque peak is reduced to match intake air reductions.