When my car was running out of fuel, one look at my stock fuel line, and I knew it was the cause and way too small to support 700whp. You have many options getting the fuel from the pumps to the rail. One idea I liked was using the stock vent line. The vent line is the same diameter as the stock fuel line and ran all the way down the bottom of the car. I wasn’t using this tube so it made sense to utilize it. So basically, all Evo's have two -6AN (5/16) lines running down from their tank to the firewall. Since I already have a Double Pumper setup, I was going to run each pump into its own line all the way to the firewall. From there it would go into a wye and then a larger -8AN would be ran to the fuel rail. This will give more than enough pipe for the fuel to flow. Keep in mind I’m running E85 which requires more fuel to the injectors.
I tried to keep the return line stock but soon realized I had problems with the 2nd pump not kicking on when it was suppose to. This turned out to be a defective hobbs switch. When it did come on, it would spike the fuel pressure causing a rich condition and making it difficult to tune that area. I believe the new twin line setup was causing some of this. Too much fuel coming in and no way for the regulator to return it fast enough. I decided to keep it simple and have both pumps on all the time using a relay to drive the 2nd pump. The problem with that is too much fuel pressure at idle. Some have gotten around this by drilling out the siphon tube. This didn’t appeal to me since the stock return line was still only 1/4” and I wanted something that was closer to -6AN (5/16) size. Unfortunately you can’t run a larger return line since it has to run through the smaller siphon tube. The siphon tube is what sucks the gas from the other tank so its a crucial piece of the fuel system. My solution was to add another 1/4” line and tee it off. This way I could run the larger -6AN into two 1/4" lines back to the tank. The siphon tube will also work and the regulator will be able to return the fuel at idle.
First step on the dual fuel feed, was to cut the vent line close to where the metal fuel line starts. A small body saw or dremel works great. Be careful not to cut the other lines since they are close. You can then bend the line down a little to gain access. Compressed air is blown backwards through the vent line to avoid metal shavings in the line.
New lines and filters installed from the pumps. Zip ties were used to keep the filters in place.
Here is where the vent line ends up. Right next to the stock fuel lines under the brake master.
Here's the new wye. It has two -6AN fittings at the bottom, and -8AN at the top. It also comes with a threaded hole for the fuel pressure sender which is added. Bracket is made out of alum. that will hold it in place to one of the bolts on the brake master.
Here it is installed with both lines attached at the bottom. I tried to route the fuel lines around the brake lines using a 45 degree and straight fittings at the bottom. The wye and some fittings were left overs from another project so its not show quality here but it works.
Other shots farther away-
I also made a custom regulator mount that uses the factory bolts.
The new -8AN fitting at the fuel rail and the -8 hose connecting it.
Here's the top of the fuel pump assembly. Hard to see everything but the square brass fitting at the top is the 2nd return line. The 1st return line is underneath the larger hose on the left.
Hopefully this helps someone wanting to do a custom dual feed fuel setup. There's other ways you can do this but this is how I did mine. Let me know if you have questions.