Project SR E30: Part 4 – Driveshaft, Fuel System and Paint
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 ?” 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.


  1. Is there a reason people avoid the AN lines with nylon/fabric braid on the outside?
    Why risk the damage caused by the steel braid rubbing on damaging things?

  2. I built the 2nd e30 SR20 in North America about 10 years ago, I even still have the wiring harness I made. I also used a Laminova Liquid to air intake manifold, negating the need for an intercooler in the front.
    I still have the manifold too lol. I used a radiator from a Volvo 240. The heat exchanger for the intercooler was a transmission cooler from and F550 tow truck. It all fit very neatly under the hood.
    Have fun with brake booster set up, probably the suckiest part of the swap.

  3. Amazing, I have learned lot of things from your website about every thing about cars and how to repair them, I also work at a company in Dubai and learning from your website.

    1. Not enough. It eventually made contact during an aggressive shift (probably flexed the subframe bushings) and snapped the driveshaft.

      We are currently looking into shimming the front of the diff down by machining small spacers for the front diff mount and then shimming the trans up to match the pinion angle. Hopefully that will push it a bit further away from the tank (and allow us to run a bigger driveshaft).

      1. what size tailshaft are you aiming for? mine is a 3 inch and it just touches the tank, we have spaced the front diff mounts but we didnt massage the tank so our next step is to massage the tank a little and see how we go.

        1. We fit a 3″. Had to move the front AND the rear of the diff down. The rear helped the most. We used Garagistic offset diff bushings to move the rear.

  4. I know you’re wearing a respirator and gloves, but spraying catalyzed urethane paint is still a potentially hazardous proposition given the isocyanates they contain. All the fun carcinogens (read the MSDS for the paint) you’re atomizing with a spray gun can be absorbed via your skin and eyes, so maybe add a paint suit and DEFINITELY add eye protection next time you do it.

    Sorry to be a downer, but it takes pretty minimal overexposure to go from healthy to F’d.

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