Pressure Regulator Location

Background: Corvair Engine: using 2 carbs (1 each side) converted to throttle bodies using conventional injectors (Siemens 6 orfice).

Is there a reason that the pressure regulator return is placed after the injectors in a loop? If you put a regulator in the main line and "dead headed" the fuel lines to single injector on each side... would it effect flow ? If I was able to not use a return loop, I could cut the amount of fuel line in 1/2....but that would be too simple. I was going to rework it according to the attached pic unless the "injection gods" here tell me why I have lost it. Sorry about the 3rd grade art work.

Ted

something about it strikes me as odd and potentially problematic, but i'm not sure what. having the injectors as the end of the rail seems like it would keep any air/evaporated/boiled fuel in the lines until it gets pushed through the injectors, while having them the current way would allow for it to be pushed past the injectors and through the regulator and return to tank. essentially, the injectors are constantly getting new fuel passed by and through them with the normal method, and fuel stays in the injector feed rail until it goes through the injector with the new one. i would anticipate the fuel heating up some compared to normal, but i couldn't say by how much.

otherwise, it seems like the regulator would be able to keep the target pressure equally as well. at 50PSI, i'm not so certain how much of an issue vapor-lock would even be.

Looks like one injector would get full pump pressure and the other regulated pressure.

Many modern cars run a single fuel line with the regulator in the tank with the pump. Would that work for you?

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Originally Posted by Bigdav160

Looks like one injector would get full pump pressure and the other regulated pressure.

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That was my first thought but the depending on the regulator type that wouldn't be necessarily true. Its a bit confusing, but think about a common rail system with say 4 injectors and you'd have a similar set up.

Yeah, that proposed system would have unregulated pressure to one and regulated pressure to the other.

The way to do a dead head system would be to have the fuel pump to the FPR input and then the output to the injectors.

I know that a similar sysetm has been used on a Nissan inline 6, where the regulator was attached to the fuel rail input, then bypassed back to the tank, which seems rather pointless, to me.

Without the use of a PWM controlled fuel pump and proper monitoring and control circuitry, the results will likely be less than desired. Running a return or new feed line or both is not that difficult, and is a proven system that works well.

It *appears* that the proposed arrangement would provide regulated pressure to both injectors. The line from the tank and the injector connected to it will be at regulator pressure. Excess fuel will be returned to the tank. The question to me is where the 2nd injector is connected. Is it connected to a port common with the fuel inlet or with the return? If it's connected with the inlet you will have 50 psi at both injectors.

Dave's right about vapor. Programming or tuning for returnless systems should allow for a means to evacuate any vapor during cranking that's formed during hot soak or longer storage periods with longer injector pulses. Knowing how often the check valves in the GM pumps leak, I'd try to run the return system.

Thanks guys. My thought was that any pressure relief (pressure regulator) within the system would equal out over the entire system. I saw how other systems are set up, but they are usually using multiple injectors and would do that to spread equal flow over multiple injectors. As the injectors spray and lower the overall system pressure, only pressure over the FPR setting would be returned, so I'm going for it and will report my results.

I may alter the design slightly with a central FPR before the "T" to each injector (2) and have both "dead head". I cant see that "cooking" or vapor lock would be an issue as the system will energize and start spraying under pressure (40-50 psi) when the key is turned.

I have been on the lookout for fuel cups (similar to ford fuel rails) to make a small dead head injector with clips. I'm using a conventional injector and making it into a TBI setup and works petty well so I do have to seal the injector at the bottom from vacuum leak. I have designed and used one for about a year, but looks like I designed it and is a little more bulky than I like. Mine is not as bulky or as expensive as most I have saw. Pretty much just looking for something to seal the injector head and convert to a 5/6 fuel line with low profile (I dont ask for much). I have emailed this company twice about buying cups and they didnt respond.

Thanks again,

Ted
68 Corvair EFI
61 Corvair Loadside (Future EFI)

damn.. that is a nice rail!

I don't know where to source stamped cups. MSD sells a stepped drill bit that will provide correct ID for making your own cups and various companies will sell machined cups intended to mount in a manifold. I would think a custom cup with an outer shape that creates a low pressure area just below the injector would encourage vaporization of atmoized fuel before introduction into the engine to create more consistent performance.

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I'm going for it and will report my results.

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Best way to learn! Stay safe and let us know.