Cutting gas tank, doing side exhaust, adding rear diffuser.

Originally Posted by phunk

Cutting the tank in half will absolutely work great at reducing and nearly eliminating fuel starvation, and you should end up with a 10-11 gallon tank in the end because you will want to cut it closer to the driver side.

All the EVAP stuff, fill breather, and rollover valve etc is in the dead center top of the tank, and you will want to keep that stuff. So strategically cut the tank in the correct location and save yourself a lot of trouble.

Notice the photo I took from my RRP installation page and editted. The yellow areas are calling attention to parts of the tank you want to keep. When I cut that opening in the fuel tank, it was put there intentionally because lots of gizmos are attached to the top of the tank right there, and are still mounted to the panel I removed. This tank was never going into a car, it was purchased new for RRP development and now just hangs out at the shop, so it was fine for me to remove those devices.

You should cut around the red line area.

Like I mention in a PM, you need not even consider the in-tank siphon transfer hose, no need to plug anything or any considerations, just dont hook it up to the fuel sending unit anymore.

The largest struggle with this procedure to the fuel tank you are undertaking is that you will be missing one of the fuel level floats that are essentially variable resisters in a series type circuit.

The driver and passenger side level sensors have a slightly different OHM sweep range... why, I cannot tell you. But this means that fuel level has more value to the gauge on one side of the tank than it does on the other side of the tank.

If you simply bridge the 2 wires together for the missing driver side float sensor, you will basically be telling the gauge that the driver side is full. If you measure the OHMs across the sensor in the bottom position and wire inline a resister that matches, you will be telling the gauge the opposite, that this side of the tank is always empty. This would be ideal because the gauge would always be accurate, it just wouldnt ever reach the pegged full position. The only way you are going to get the gauge to operate entirely OEM like is to add that driver side sensor back in to the passenger side of the tank, which will be a hassle.

It is possible to swap the potentiometer chip inside the level sensor with chips from otherwise identical float sensors. So perhaps if you look in some Nissan service manuals for FWD vehicles that would only need a single sensor, such as maybe a maxima, its possible that the potentiometer chip from one of those vehicles is calibrated to produce the sum of 2 sensors in the Z, either that or their instrument cluster is just calibrated for a single chip of half values like the Z.

PS external surge tanks dont work out well in the 350z or 370z, which is why nobody usually tries them! However, with the tank cut in half and no more need for the jet pump off the regulator bypass.... if you still experience mild starvation with your cut tank, let me know, and I can set you up with everything you need to add an external surge tank for very low cost... you do not need rails or anything crazy. Just a little canister, a cheap walbro pump, and some hoses and fittings. Under $500 easy.