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Here is the Auxiliary Fuel Pressure Regulator. I've removed the "bleed valve" for setting the top end boost pressure. You can see the hole where it screws in. The center post adjusts the base pressure for no boost/no vacuum. The source for boost/vacuum pressure is the brass fitting.
Here is the top chamber opened up. There is a washer and spring that presses on the center of the diaphram. The arrows show the two holes for signal sources and the bleed valve.
Lifting the diaphragm up you can see that it has a piston attached which passes into the lower chamber. The center post on the outside increases and decreases the tension on the piston regardless of the pressure in the top chamber. (Which is why it sets the *base* pressure!)
Cool colors huh?! Here you see the lower chamber. The left side has the two openings. The center one is where the fuel enters the regulator and the "moat" is where it leaves. The diaphragm has a metal plate on it that is pressed over these two holes (or hole and moat).
Now you can begin to see the whole operation. The piston comes through the hole on the right and presses on the back side of the diaphragm, forcing the plate over the openings...driving up the pressure in the fuel rail.
Here you can see the piston coming through the center section.
a)is where the boost pressure comes in and presses on the diaphragm forcing the piston b) through the center section c) and onto the back of the lower diaphram d). The plate on d) is pressed onto the opening e). Since the fuel cannot pass through when the pressure is up (caused by boost) then the overall pressure in the fuel rail to the injectors rises as well. The bleed valve across from a) on the outside allows you to adjust how high the pressure will go in the top chamber, thus changing the full boost fuel pressure. Very nicely done Corky! BTW if you have "honking" in your AFPR you just rotate the upper diaphragm and put it back together.
This is my somewhat modified setup. The inline needle replaces the restrictor and allows me to open it up a bit for a quicker boost rise. The small check valve that comes with the kit locked open on me on occasion...I think from the heat. This is a distributor check valve and is much more robust. The Napa part number is 2-970 out of the CRB line. With the two valves I'm able to dial in a quick rise in Fuel Pressure and still hold the top end pressure down. Running 1.8L injectors on my 1.6L w/stock timing I've got 12psi boost with no pinging in hot weather! [UPDATE: later in 100 plus temps and more advanced timing and CA gas I got pinging. You MUST lower the boost if this occurs until cooler weather returns. NO pinging is acceptable. A small ping once in a while is NOT acceptable. Trust me.]