THEWITCHKING

iTrader: (3)

What is the advantage of deadhead vs boost referenced? And why would one need to t off the fuel return?

Jeff20B

iTrader: (13)

The Nikki should be deadheaded when you use it for boost. The carb is deadheaded. Not necessarily the fpr. It's a term used to describe how the carb is plumbed. Does that makes sense?

Are you asking about the T idea I came up with? It is mentioned in my post but I'll say it again. I added a 3/8" fitting to the bottom of my tank. This lets me use both stock fuel line fittings at the top of my tank as returns. This should reduce potential backpressure in the return line to "low enough" so I can use a Mallory boost referenced FPR on a Nikki. The Nikki runs anywhere from 2.5 to 3 psi. The Mallory can be adjusted down to 3psi. I hope this 3psi lower limit will be low enough to not bother the Nikki. If my return line has any restrictions, the carb might see 3.5 psi or more, which is something I'd like to avoid.

As for the T fitting itself, it will be one of those common barbed brass T fittings made in china you can find at any auto parts store. But if it looks like it's going to be a restriciton, I'll come up with something better made, or maybe with a larger inside area. I don't know much about fluid dynamics, but if it looks like it'll work, chances are good that it will.

PercentSevenC

I've turned it down as low as 1 PSI with no issues with my MSD pump and stock 12A 1/4" tank return. The Nikki should be fine.

stevensimon

iTrader: (11)

fuel system is more involved than i was expecting. im going to have to figure this out when i start plumbing my setup.

there is a tee on my banjo fuel line for the webers. im assuming the smaller dia is return and the larger is feed. was thinking that i could send the smaller back to the tank and have the fpr return tee into it with a check valve so it doesnt repressure or backfeed the carb. didnt think about restrictions though.

does anyone know of a fuel pump that only puts out 20psi max or so? i dont want a typical efi pump charging my lines to 40+ every time i run the thing.

PercentSevenC

I don't know if I'm understanding your idea correctly, but it sounds like what you're thinking of won't work. Just block off the return fitting on the carb and run the FPR's return line back to the tank.

For the fuel pump, just use a normal EFI pump, like a Walbro 255 or an MSD 2225 or something. The lines will not pressurize above where you have your regulator set, assuming your return line is adequate. I ran a 5/16" return line back to the 1/4" tank inlet and had no problems.

LizardFC

iTrader: (1)

Interesting, what's the output pressure of that pump?

I was looking through my stuff and just realized that I bought a Walbro GSL392, which is an EFI pump rated for 60 PSI. OOOOPS. Not quite sure what I was thinking on that one. It's been a year since I started ordering all of this stuff and I keep finding surprises in all these boxes of parts. There's no way I can regulate that down to where I need, is there?

Jeff20B

iTrader: (13)

I think the outlet pressure can be anything up to the pump's rated capacity limit. So for example a stock Cosmo rail fpr runs at 35psi and can boost reference up to 43.5 or so. Maybe higher? For many running higher power, they change over to an adjustable aftermarket fpr and run dual lines, one to each rail, then T them together into a single return back to the tank.

As for carb pressures, I plan to throw a walbro 255 in my rotary baja hooked up to a Mallory 4309 with the boost reference nipple open to atmosphere. This lets me get the fuel system installed and in place for a future turbo upgrade. But in the mean time it will be adjustaded down to 2.5psi for the NA Nikki, which according to PercentSevenC is possible with an EFI pump, while I work the "bugs" out of the chassis.

PercentSevenC

Your pump flows a bit more than mine, but it should still be alright. As long as you can get it to hold your base pressure steady at idle, you're good to go. A larger return line (5/16" or even 3/8") will help, though you'll have to adapt it down to 1/4" to go into the 12A tank. Worst case scenario, add a larger return fitting to your tank.

stevensimon

iTrader: (11)

so youre saying i dont need a return line for the carb itself?

PercentSevenC

Correct.

LizardFC

iTrader: (1)

Yeah, I'm probably going to have to make a custom return line and fitting in the tank. Really looking forward to that little project. I'll be sure and take pics. If the pump is too much for my regulator or the new line, I can probably drop the voltage to the pump using a resistor with a heatsink. I'm thinking I won't need more than 20 PSI of total pressure with a base pressure of 3 PSI. I'm going to run as little boost as the wastegate will allow starting off and no more than 12 PSI after it's tuned.

cshaw07

iTrader: (14)

i made a sump for my gas tank and ran new 3/8" feed and return lines for mine.

85TIIDEVIL

iTrader: (2)

I stumped my tank w a baffle, 1/2" feed, and two 3/8" returns. One return is off the regulator (Mallory 4309 nipple referenced to atmosphere / nothing) and the other off the stock return from the Nikki. Pump is only a Holley Blue regulated to 3.5 and fuel keeps up so far at top end even with also feeding the 100 shot of nitrous, however it has only been for short blasts prob most to a mid 4th gear pull.

I did somewhat the same thing on my TurboII just to get her moving again and or maybe experiment w/a blow thru setup. Stock TurboII tank and EFI pump, 1/2" feed w/a 3/8 return. The return is off the Mallory regulator 4307M (4309 can't regulate that high of an EFI pressure low enough, although the mustang guys I read on their forums have had sucess changing out the rubber diaphragm to up/lower the 4309's capabilities) and the Dellorto is deadheaded. Car runs good soooo far and pressure is regulated down to 4ish psi. I haven't made any hard pulls yet but she idles fine and drives under normal conditions fine. Regulator is referenced to atmosphere also for now.

LizardFC

iTrader: (1)

I'm not the biggest fan of welding on fuel tanks so I'll probably stick to the stock pickup. What was the advantage to running a second return off of the Nikki?

85TIIDEVIL

iTrader: (2)

I couldn't get my fuel pressure gauge inside the car to read right... I was trying everything to solve it, turned out being a bad isolator. The Nikki's return stayed since it didn't give me any problems.

LizardFC

iTrader: (1)

Update on this... I got the Aeromotive 13301 and the Walbro GSL 392 installed. I ran a new 3/8" steel return line from the regulator to the tank. I removed the vent line that runs from the tank to the neck and plugged my return line into that inlet (thanks to ArmyOfOne for the idea). Yesterday it fired right up and pressure held steady just under 3 PSI.

But today when I started it, the pressure shot to about 8 PSI and I can't figure out why. Naturally it started to run rich and die as the fuel level in the carb became excessive. So it seems like the regulator can't handle the pressure coming from this pump. Not sure why it was fine yesterday though. I took the gas cap off to make sure the tank wasn't building pressure and there was no effect. I would think a dedicated 3/8" line would be enough for a return. I also have the stock return still hooked up to the carb. I may try to tee that in somehow to bleed off more pressure. Or just buy a wimpier pump

Any thoughts?

LizardFC

iTrader: (1)

On a positive note, it starts up really easy in the cold thanks to the pump making it run stupid rich at idle. I ordered a couple high watt low ohm resistors to drop the supply voltage on the pump. Hopefully that'll drop the flow down to a level that the 13301 can handle.

Jeff20B

iTrader: (13)

I have a simailr problem with a Mallory 4309 and a walbro 255. It will not run under 5psi for my Nikki. I had to add another dial type pressure reg between the mallory and the carb to get it down to 2.5psi.

My solution is to swap in a 40psi 43gph MSD pump. Or get a EFI FPR to mount in front of the mallory. Or get an aromotive boost referenced FPR which may solve the problem, or not.

My send line is 3/8. Return is 5/16 which could be the problem too, but kinda doubt it. Gotta be the walbro so the MSD pump is getting swapped in to check.

LizardFC

iTrader: (1)

I think the Walbro is just too much pump for such low fuel pressure unless you're running a massive return line. The regulator I have is the Aeromotive 13301 boost referenced FPR. So that won't solve your problem. It's rated for up to a 250lph pump, so I figured the 255 would be okay. Guess not It held 2.75PSI with my Holley Red so I know the FPR is good. My return is 3/8" and increases 1/2" just before the pump.

If I can drop it to 8-9v with resistors then it'll probably be okay. Hopefully those will come tomorrow. If that doesn't work, I'll deadhead the carb and tee in the 1/4" stock return and see if that helps.

LizardFC

iTrader: (1)

UPDAAAYYYYT...

Ordered two .2ohm resistors and installed them. Apparently I got my math wrong because even in series the voltage barely dropped a volt. Fuel pressure was about 9 PSI. So I ordered a couple 1ohm 50W resistors which came today. I installed one and the voltage dropped to ~10v running, leaving me with just under 3 PSI at idle! So I mounted it on a piece of aluminum next to my new pump relay. I'll keep the other one as a spare. Hopefully it'll hold together for rallycross this weekend. Then next week I can begin boost prepping the carb.