Honda Prelude Message Board, Pictures, Forum, Specs, Performance Mods

Fuel Pressure Mod

After installing an intake, header and exhaust the car will have a ton more airflow which is good, but it can be bad if you don't have some extra fuel to balance it out. Many people like to install adjustable fuel pressure regulators but they're a pain in the ass because they have to be tuned constantly and the correct way to do it is on a dyno. Not many of us have a dyno handy all the time and even when there is one in town, it costs a lot to use. The stock fuel regulator gets its pressure by vacuum pressure, which is usually constant. If you want more fuel pressure, unplug the line connecting the fuel regulator with the intake manifold. Now the regulator can suck in as much air as it wants as it's no longer limited to the vacuum tube pressure. So find the line that goes from the regulator to the manifold and remove it. Cap off the opening from the manifold where the vacuum line went. However, DO NOT cap off the regulator! If you cap off the regulator it defeats the whole purpose cuz you will be stopping all airflow to the regulator. I saw someone put a K&N breather on the regulator. this is pointless. Nothing is going to fly into the 1/16" hole. Your idle may change a little due to the change in vacuum pressure, but that's something you'll have to get used to. Several people have done this and been very pleased, and I have had some excellent results as well on many cars.

Stock 95 Civic DX(Automatic)
With air box removed - 17.4@80mph
With air box removed and fpr mod - 17.0@80.5mph

Stock 95 Del Sol Si(SOHC VTEC, 125hp)
Air box removed, timing advanced, adjusted tire pressure - 16.0@87mph
Air box removed, timing advanced, tire pressure, fpr mod - 15.8@88mph

92 Prelude Si(my car)
All mods listed including SX adjustable regulator - 14.6@94mph
All mods with fpr mod(SX disconnected) - 14.5@94.6mph

Yes, I got a better time with the fpr mod over the adjustable SX regulator.

This is where the regulator vacuum line connects to the intake manifold. On a stock car it's not a yellow line, but look in this area for a line connected to a gold diaphragm. Don't mistake with the flapper valve diaphragm, the fuel pressure regulator is the smaller gold diaphragm located on the fuel rail.

Page Modified: June 24, 2007
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