Quote:
Originally Posted by xlr8or
Eric it can be done with your existing tank. Did this exact thing to a friends SPF. Fab up a 1 gallon surge pot and feed the FI from there with -10. Run the FI return line (probably -8) to the surge tank and then vent the surge to the main tank return (-6). Use a standard electric pump from the main to to the surge tank (-6).
This way the small fuel pump only has to keep up with the fuel that is actually burned and the big pump always has a steady supply.
Works great and you don't have to mod the existing tank.
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Guys,
One thing to consider when building a system like this for street use relates to fuel heating and associated cooling needs of the fuel pump. These problems become more important in higher horsepower (500 hp+) applications where a larger pump is used. Pumps capable of supporting high horsepower applications will heat the fuel some as they cirulate it. A larger tank provides more cooling area and a large reservior of fuel to allow the heat that is generated to disipate. In high HP applications, you might also consider a fuel pump controller which will run the pump at a lower speed below a certain RPM point (say 2500 RPM) which helps to limit fuel heating, makes the pump quieter in the RPM ranges where you can hear it, and helps to extend the life of the pump. As far as fuel line sizes go, I would say that -8/-6 for the feed/return lines would be the minimum size to use. -10 from the tank to the pump is a good idea and you want to try to mount the pump below the tank if possible. You should also plan to use a pre and a post filter before and after the pump. You have some important choices to make relative to your fuel pressure regulator also. The best setup would be a vacumn reference regulator if that works with the intake manifold that you will be using. This involved running a vacumn line for a common plenum that averages the vacumn reading from each runner on your intake to the regulator. This setup ensures a constant pressure difference across your injectors which in turn improves the accuracy of their ability to meter fuel. This is not essential on a naturally aspirated setup but it will improve drivability a bit. I do not have this type of regulator on my Cobra's TWM setup but I do use it on my blown Vette motor (see below) which sees a much greater range of intake pressure variation from cruise to WOT. I would recommend that you install a quality fuel pressure gauge and/or a sensor which will let you see or record your fuel pressure while you operate the engine This will be needed to accurately setup the fuel pressure initially and will give you a means to ensure that you have full fuel pressure when you entine is operating at full load. A fuel pressure sensor which can be read by your ECU is also helpful as you don't need to add a gauge to your dash which was not there on the orignal cobra (or be trying to watch it when you should have your eyes on the road). Good sources for filters/pumps/regulators would be either Weldon or Aeromotive.
I am using an Aeromotive setup on my Cobra to feed a 482ci FE motor with a TWM intake making about 650 hp. The pump and one of the filters are mounted inside the driver's side rear fenderwell. I am also using a fuel pump controller set to switch the pump from reduced speed to full speed at 2400 RPM. This device also functions as a fuel pump relay and would require connections for RPM, FP Relay Control from the ECU, and an hi-speed override switch to be run from your dash area. I am using a stock ERA aluminum tank with a return line fitting and tube installed on the passenger's side (the fuel pickup is in the middle of the tank). I am not running a sump. My lines from the pump to the engine compartment are both made from 1/2" ID aluminum tubing (equivalent to -8 feed and return lines). I am using the fuel pressure regulator which came with my TWM intake (it is not vacumn refenced). The following are some pictures of my setup for your reference:
This is a picture of the fuel pump and post filter. The pre filter is mounted on the front of the tank and cannot be seen in this picture.
This picture shows the fuel pump controller (box on the left) which is hidden behind a removable panel in the trunk.
I've mounted a set of toggle switches under the dash on the drivers side. One of these controls the hi-speed pump override which forces the fuel pump to run at full speed no matter what RPM the motor operates at. This is useful if the car is raced. BTW, the other switches control a remote battery cutoff relay, a dash indicator which can be used for either the ECU's "check engine" light or as a "shift" light, an enable switch for the 2-step RPM limiter, and an enable switch for the ECU's on board data recorder.
Just for reference, this is a picture of the fuel pump and tank setup on my Blown and Injected Vette which feeds a 383 ci SBC making about 625 hp:
This system uses Weldon components and does not use a fuel pump controller. I purchased a new stock tank and modified it for a sump and a return line fitting with a tube which is on the passenger's side of the tank. I built a bracket to hold the pump, pre and post filters, and fuel block to install everything neatly of the cross member in fornt of the tank. Both of these setups feed motors which are making 600 - 650 hp. The vette motor (shown below) has higher fuel requirements that the Cobra motor due to the supercharger.
You can see the Weldon boost/vacumn reference fuel pressure regulator mounted on the back of the supercharger (is the gold and black part).
I would use either of these setups again on a street driven vehicle. Its probably best to get a new replacement tank for your car and have it modified if that is possible. Many welders will be a little relucant to try to modify a tank that has been filled with gasoline for obvious reasons.
I hope all of this information helps you.
- Fred
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