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Fuel System Flow Mod (Honda)

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Easy fuel system modifications.
#1 Fuel line exiting the fuel filter

The Problem

The combined areas of the two side holes on the top fuel filter bolt do not add up to the area of the input hole on the bottom. This creates a flow inefficiency.

*Pictures courtesy hondatuningmagazine.com

The Creative Fix

Drill out the existing hole. I found that a 3/16" bit is just the right size to widen the hole without sacrificing structural integrity.


The new 3/16" hole will increase fuel flow efficiency by eliminating this bottle neck. I also drilled a 1/8" hole through the bolt on the opposite axis as the 3/16" hole to free up flow even more.

#2 Fuel pump circuitry

No pictures, sorry.

In short, if you were to put a volt meter on the circuitry at the fuel pump you would find a lower voltage then at the battery terminals with the car running (about 1.5 Volt loss). This is caused by relays and normal car wiring but translates into about a 7.5% loss in pumping efficiency. A quick mod is to run a 12 gauge wire directly from the +12v battery, through the switch side of a head light relay, and then to the pump. Run a new ground with 12 gauge wire to a GOOD grounding point. Hook the existing fuel pump +12 to the control side of the relay to turn it on when the ignition is turned on. This will allow the full amount of electrical flow to the pump.