So for my NB Miata swap, I am confused about the fuel lines required as the NB is supposed to be "returnless" but there are two lines coming off the fuel rail. I will be using a NB Miata in-tank fuel pump assembly but it appears to have two lines coming out of the top and I have two lines coming off of the fuel rail. Since I have to run all new lines on the Spitfire frame, I need some guidance or if someone can point me to a simplified drawing as I don't need the charcoal filters and other emissions stuff on this, as this has a non sealed gas tank, etc... so just need a simplified drawing of what is the minimal requirements for the fuel system?
The NB is "returnless" in that there is only one hard line that goes up to the engine bay, it still comes out of the tank so that the fuel filter can go between the pump and the regulator and also be accessible to for service. The factory routing is:
pump -> exit from tank -> fuel filter -> tee -> return into tank -> in-tank regulator
And the other leg on the tee goes forward to the fuel rail/etc.
If you want to convert it to a return-style routing you just remove the tee & the in-tank regulator, connect the filter straight to the line forwards, install a new fuel rail & regulator up front, and add a return line.
I'm not sure about the charcoal canister stuff though, the EVAP system has always been a little mysterious to me.
Okay, so I understand the tank/regulator/filter piece, but on the engine are two fuel lines off of the NB rail. one is connected to the FPR on the rail and the other is connected to the end of the fuel rail . So I have two lines running off of the fuel rail. Does there need to be a T in this line and then this would connect to the single line running to back to the tank/pump/regulator?
dherr said:
So for my NB Miata swap, I am confused about the fuel lines required as the NB is supposed to be "returnless" but there are two lines coming off the fuel rail. I will be using a NB Miata in-tank fuel pump assembly but it appears to have two lines coming out of the top and I have two lines coming off of the fuel rail. Since I have to run all new lines on the Spitfire frame, I need some guidance or if someone can point me to a simplified drawing as I don't need the charcoal filters and other emissions stuff on this, as this has a non sealed gas tank, etc... so just need a simplified drawing of what is the minimal requirements for the fuel system?
Looking at pictures, it appears that the "returnless" part is poppycock. If there are two lines, one on the rail and the other off the regulator, then you've got a feed and a return. Whether this return goes to the tank or the filter, its still a system with a return.
Run the high pressure fuel into the rail opposite of the regulator and return it to the tank/swirl tank/filter via the line from the regulator. Connect the vacuum line to the regulator and you're good.
NB fuel rails only have one fuel line connected to them, the one with the GM-style click-connect fitting on it. The thing on the 2-bolt flange is a pulse damper, not a regulator, and it is a dead-end piece.
To convert to a return system, you can remove the damper and replace it with a regulator or an adapter to go to a remote-mounted regulator.
Stefan said:
Looking at pictures, it appears that the "returnless" part is poppycock. If there are two lines, one on the rail and the other off the regulator, then you've got a feed and a return. Whether this return goes to the tank or the filter, its still a system with a return.
The "returnless" part of the NB system means that there is only one fuel line that goes from the back of the car to the front of the car. Once fuel goes up that line, it never returns to the tank. Most cars built in the last 15-20 years do this because a trip through the engine bay heats up the fuel and that increases evaporative emissions.
Okay so the plot thickens.... My car is using an JDM 1999-2000 NB1 engine (BP4W). Looks like the Japanese market cars do have a different fuel system. See my fuel rail and thus my confusion.
So my guess that to make this easier and also to make tuning with the Hydra the same as a US spec car, my best bet would be to get US spec fuel rail with the pulse damper as I already have the Fuel pump/regulator pieces for an US NB and want to be able to tune this properly. That way I can run the single fuel line and keep it simple
Yes, that's definitely different. :)
The Hydra mostly won't care about return vs non-return. You could convert it to return if you wanted, that has some minor advantages if you're going to run a bunch of boost and thus use upgraded fuel pump, regulators, injectors, etc. If you're just going to keep it to stock-ish power levels then it doesn't really matter.
So after much googling, I have deduced that the simplified system consists of the following:
Russell -6AN to screw on EFI adapters for the fuel pump and regulator lines
Two -6AN lines running from the fuel pump/Regulator lines to a -6AN Tee
-6AN line to a inline -6AN fuel filter
-6AN line to the engine fuel rail (Stainless Steel braided fuel line with 1000 PSI rating)
Another Russell -6AN to screw on EFI adapter for the fuel rail
That should do it, ordered all the parts from Summit, should have this put together next week
If you're running stock-ish power levels (and thus don't need the upgraded flow of the -6AN over the stock lines), you can put a couple of the quick-disconnect adapters on the stock filter, rather than using the -6AN one. I'm not sure which one filters better, but a factory filter is significantly larger than the inline AN ones I've seen, so presumably have more filter media in them. They're also a lot easier to find at a FLAPS when it comes time to change it. :)
I'm also wondering if the filter should go on the outlet line from the tank, before the tee? That would allow the regulator to compensate for restricted flow through it, and also filter the gas that's getting returned to the tank.
Not stock but not crazy either. I have a small turbo, uprated injectors and are looking at around 10 pounds of boost for around 200-210 HP. Since this is an engine swap, I don't have a filter, so it is all being pieced together. The Flying Miata big fuel kit has the filter after the tee, so I would assume this should work fine. I'll put the filter in a location that I can easily check it (most likely in the engine compartment.
