Fuel Plumbing Fun
This mini fuel rail has a feed port, an output port, and a return that flows through a stock Miata fuel pressure regulator. Either of the brass ports can be the feed and the Miata regulator will keep the fuel in the mini-rail (and the fuel going downstream) 43 psi higher than the manifold. If you happen to have a Hayabusa engine that wants a fixed 43 psi, this same system will work, just don’t connect a vacuum line to the fuel pressure regulator and it will reference to atmosphere.
I mounted the regulator rail to the brace on the back of the bellhousing adaptor. This will be the only Miatabusa with a separate regulator rail like this. Future adaptors will extend high enough to bolt directly to the cylinder head, making the whole assembly more secure, and the port for the fuel pressure regulator will be machined directly into the bellhousing adaptor.
Tiny detail downstream of the regulator: The fuel feed faces the wrong direction. This could be solved with a little loop of fuel hose, but there’s a more elegant solution.
Unscrew the rail and it’s actually a series of plastic injector mounts with connecting fuel pipes.
Turns out the feed pipe is directly interchangeable with the connecting pipes, so you can assemble this fuel rail however you want.
Simple! This feed line is also designed for an O-ring sealed hard plastic fuel pipe, so there is no barb to hold on a conventional fuel hose. Once you remove the grey plastic doodad, there is a steep hump that some 5/16 fuel hoses will actually push over, provided you talk sweetly and use lots of lube. If you manage this, put the hose clamp on the far side of the hub and you’re set.
I used 300-psi GoodYear fuel hose, though, and it was too beefy to stretch over such a big hump, so we had to use a brake line flaring tool to put a little hump on the end of the pipe. Without the hump, a fully-clamped 5/16 fuel hose could still be pulled off by hand pretty easily.