Nikita Rushmanov posted on April 01, 2018 16:01
We drained the fuel tank and then dropped it. Dropping the tank ended up being a 2 hour ordeal, something that takes 3 minutes on an S-chassis. The fuel tank doesn’t clear the subframe, so it will not simply drop down. You instead have to tilt it, move it down a little, tilt it some more, move it down a little, until it drops. On top of that, the filler hose is wedged directly between the subframe and the chassis, making it extremely difficult to remove.
We used an endoscope to find the position of the crossover tube inside the tank. We didn’t want to damage it when we bash in the tank.
When doing this, we actually became extremely curious as to how the fuel is transferred through the crossover tube to the other side of the tank, since there is only one pump. Turns out, it uses the venturi effect. The fuel is pumped to the engine from the right side of the tank, but it returns to the left side. The fuel return line enters the tank at the bottom, where there is an orifice. When the fuel goes through this orifice, its velocity increases. At the point of this velocity change, there is a Tee to a syphon tube. Thanks to the venturi effect, as the fluid velocity increases, it creates negative pressure around it, sucking fuel through the syphon tube and into the crossover pipe, which takes it to the right side of the tank.
After some light massaging, we have about ⅜” of clearance between the fuel tank and the driveshaft.
During the driveshaft test fit, the car was supported by jack stands placed underneath the rear subframe. This means that the subframe bushings were compressed to their maximum limit, as normally the load of the car rests on the spring perch on the chassis instead of the subframe. This means that when the car is taken off the jackstands, we should have even more clearance to the fuel tank as the bushing relaxes.
Since we had the tank out, we decided it’s a good time to swap out the fuel pump. Since we are doubling the power output of the car, there is no chance the OEM fuel pump will keep up. We decided to upgrade to a Walbro 255 lph pump.
We ran into a small hurdle when installing the new pump. The pump inlet doesn’t quite fit inside the bracket, which meant that we were unable to put the sock on.