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I'd like to share a pretty sweet mod that I completed a year or two ago. The reason for the delay in sharing is that I wanted to make sure that everything was going to survive adverse weather conditions as well as my personal beatings. Lo and behold, everything is still in one piece and still working great!
A little background
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For those that are unaware, one of the differences between the AP1 and AP2 is the fuel system. The AP1 system has an extra fuel line to return fuel from the rail back to the gas tank. In addition, the pressure regulator is attached to the fuel rail rather than sitting inside the pump hanger. It is also a different type of pressure regulator with a vacuum reference port. While this makes no difference to a naturally aspirated engine, the difference is massive when you add boost. And guess what? I added boost. The problem comes from the pressure that the injectors have to fight against. In a N/A engine, there is always vacuum in the intake manifold, so there is never any resistance to the fuel squirting out of the injectors. However, when you add boost to an AP2, now the injectors and fuel pump have to work harder to overcome the now positive pressure in the IM. By having the pressure regulator on the rail with a vacuum reference port, you can vary the amount of pressure regulation as the boost increases (usually a 1:1 ratio). In other words, you can raise the fuel pressure at the regulator to compensate for the new impedance at the injector opening. Suffice it to say, my high cam fuel curves before and after this mod are night and day different. Now, on to the goodies!
The actual mod
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There are 5 main things needed to accomplish this mod:
Modified fuel rail to accept a pressure regulator
Pressure regulator + vacuum line
AP1 return line + brackets
Modified clutch slave cylinder hard line bracket
AP1 fuel pump hanger
And here's how I pulled it off:
Here you can see that I decided to modify my AP2 rail. I bought some 304 stainless tubing and 304 mirror-shine stainless from Mcmaster-Carr for the regulator mount. Welding was performed at Yes Welding in San Jose, CA. I was honestly guessing about the fuel rail material, but I guess I lucked out assuming carbon steel. The boys at Yes Welding went with a TiG weld. On the very left is a pressure sensor. You can also modify an AP1 rail and expand the injector holes to accomplish this part of the mod.
Here is everything installed. Perfect fitment! I went with an AEM regulator for a Civic. Even with an AEM 320 fuel pump, I still have the adjusting screw all the way in to achieve the desired 55-62psi of fuel pressure according to the service manual.
Here is the stock clutch slaver cylinder hard line bracket. Unfortunately, it blocks our new fuel line!
And here is my fab job out of good old polycarbonate. You can see the AP1 return line running directly to the right of it.
This little guy was by far the hardest part of the mod. I probably scrapped about 20 of these bastards! It's a bracket the holds the new fuel line to the existing fuel lines. Unfortunately, the AP1 fuel line brackets don't work on the AP2 due to the lines have different diameters.
Locktite is an absolute must! However, even if every single bracket failed, the line is light enough to stay suspended and not get damaged.
And the last part of the mod--the Frankenstein fuel pump hanger. Thankfully, the AP2 fuel float assembly clips right into the AP1 pump hanger. One very strange quirk about the AP1 vs. AP2 pump hanger is that the positive and negative leads to the pump are reversed!
This connector must have the pins reversed. You can imagine my dismay when I turned the key for the first time and saw 0 psi of fuel pressure.
In addition, you will have to notch the metal disc at the top (with the bolt holes) at 1 new location to allow the hanger to sit in the tank in the correct orientation:
Yes, I cut the wrong spot the first time.
Unfortunately, the fuel line nipples are clocked slightly differently at the top of the AP1 hanger, so the existing feed line will have to be twisted a bit to clip onto the AP1 feed nipple. This is really the only part of the mod I wasn't 100% happy with, but I haven't had any issues with fuel pressure so I'm not tripping. I have since remedied this by buying the AP1 fuel feed soft line that connects from the nipple to the hard line. I should also mention that the AP1 feed line DOES NOT work with the AP2 feed nipple.
Conclusion
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Well, there you have it. One AP2 return-style fuel system good to go! Total cost was a little over $400, not including the polycarbonate I had sitting around from yesteryear's mods. Not too shabby!
Looks good! I just did this as well, but I went with the SOS pre-made “return system conversion” kit. It was a little bit more money than piecing it together myself like you did, but I wanted the instructions and to make sure that I was doing the right thing and not breaking something. Lol. I also chose to go the AEM rail and had SOS bore it to fit my DBW injectors, and I also went from a FB340 pump to a WB450. Definitely made a difference though: I was able to go from 10psi at 90% fuel duty cycle to 15psi at 80%. Wayyy better mid range torque too!
Can't go wrong with SOS! Like you, I was touching 80% duty cycle with the SOS supercharger kit, 12psi pulley, ID1000s, and hard-wired Walbro 255. Anything over 80% duty cycle for port injection is dangerous territory indeed.
In lieu of running a factory hardline I guess a -6 an ptfe braided line would be the next best thing? Looks like the older style rubber braided AN lines are not best with e85? I found from a previous post these Russell part numbers for the push to connect oem fittings:
Russell -6 male to 3/8" female #640850
Russell -6 AN male to 3/8" male #640940
Hello @SlowTeg , apologies for the super late reply, but I lost interest in the car earlier this year. Now like a typical car junkie I am back with an even worse addiction lol.
As far as E85, yes you will definitely want to upgrade every part of the fuel system--lines, pump, and injectors.
Loctite? Into polycarbonate?
You need to be really careful what you use there or all the common ones it'll craze and crack, or crumble like powder, they're not chemically compatible, the solvents attack polycarb.
DIY AP2 Return-style fuel system
