Kenshi is right. It's where the fuel flows through to get to all the injectors to be sprayed. The stock fuel system on the Altima can handle a lot. The first thng needed to be upgraded will be the injectors. It is confirmed that you can use the 300ZX injectors from a 94 twin turbo. They are a direct swap. But that's not until you're sprayin a 100 shot of NOS or runnin a turbo. I wouldn't worry about a fuel rail. It's not necessary for ya, until what i just mentioned, NOS or Turbo.