I need some help setting up my fuel system so I can safely spray about 150HP of nitrous...

My setup is a Holley Black elec pump, mr gasket glass see thru filter, stock 3/8" lines up front to a Mallory 650-4309 regulator, 2 ports to the carb, one to the fuel solenoid and one return to tank. Fuel pressure safety switch hooked in to the nitrous setup...

Heres what ive done so far..
Set the safety switch at 4.5psi so if it drops any lower than that, the nitrous solenoids wont open...
Then set the regulator to 8.5psi, and made a run with the nitrous bottle closed... and when I got on it, the fuel pressure safety switch intermittently completed the circuit on and off ever half second or so. So im guessing the FP dropped over and under 4.5 that often...

SO I came back and set the FP to 9+ the max the regulator would go... it was bottomed out on the adjustment... Took it for another run and it did the same thing ever half second or so, but then it would be ok for about 4-5 secs continuosly... still not consistent for spraying though.

Any ideas on what to do now?? Ive gone through 3 FP regulators and replaced the safety switch already...

TIA - Chris

 

I am guessing the the fuel psi cutout switch is to close to the fuel solenoid.It has to be at least 12 inches or so from the solenoid like right after the fuel pump outlet

 

Don't know alot about the Nitrous. But from what I have learned, change out that glass fuel filter. Fire waiting to happen!!!!

 

 

Im almost certain its 12 inches from the fuel solenoid... and it is located right on the outlet of the regulator... If I move it right after the pump, which is located right by the tank in the rear, would that get a correct reading since its before the regulator?

Thanks again everyone... ohh and ill definitely replace that glass filter! maybe that thing just can't handle all the volume needed.. lol

 

I believe that would be a better place for it.Its job is to make sure that the pump is putting out a enough pressure.I am not a expert but do have some experience.The only written info I ever read on fuel psi cutout switches was the install manual for the Jacobs Nitrous mastermind.I don't own this system but it uses a cutout switch and thats where I got the info about the 12 or so inches.You can download a install manual to see for yourself at Mr gasket .

 

I went ahead and read that manual... I actual have a Jacobs NMM in the car, and thats how i know the FP switch is cutting in and out... I love the NMM for lil reasons like that...
I am going to try and move the FP switch to directly before the regulator and see if that helps.. im afraid to move it all the way to the back, since its a pain to run those wires, lol, AND i figured there could be loss of pressure from the back to the front, and the bottom line is making sure there is enough fuel AT the solenoid!?
I guess ill try moving it back a little at a time for now...
Do you all think that having the return line could be keeping me from keeping my pressure up high enough?

 

I went ahead and fixed something with my fuel system, which I posted in another thread as well...
First I had a glass filter before the pump, so thats 2 no-no's in one! Put a fuel line directly to the pump from the tank.
Then I found a Earls in-line filter I bought a while back, and installed that right after the pump.. and from there the stock steel 3/8" line all the way to engine bay.
Directly before the regulator, I put the FP safety switch, which definitely makes it at least 12" before the solenoid.
Unfortunately I cant go out and test it since its raining here!!

I just found another problem with my whole setup though!
I read the instruction sheet for my Mallory regulator... It says to remove the adjustment screw and the FP should be less than 3psi or a bigger return line will be needed. And of course when I do this, mine stays above 5psi! They suggest for my pumps free flowing rate of 140gph, and guesstimate of return line length of 15 feet, that I need 5/8" size return line.. This is insane!
Any thoughts on this return line stuff affecting correct FP under load, and fuel starvation while spraying nitrous?? I would this this would cause the FP to stay high enough, and wouldnt cause a problem??

Edit - Ughhh... Just an after thought... If I do need a bigger return line, even if I run it all the way to the back of the car, the fitting on top of the tank is still on 1/4 or so... So ill have to drop the tank, and have a larger bung welded in. If I do that, I might as well have them weld in 2 larger bungs for the tank outlets or a sump in the tank! More money just to get this nitrous working

 

Running a 150 shot should not be this complicated. First, a Holley black pump is plenty for a small block and a small plate shot. I am not a fan of the Hobbs switches, but for nitrous newbies it gives them a sense of saftey.

A few observations; if you get the system to work (and not cut off due to the Hobbs switches) you are going to have a very rich setting for the nitrous. You do not want 9 psi of fuel presssure on the nitrous side, it will drown your motor and not make any additional power. If it were me I would get rid of all the little fuel filters and run one big one. I would also get rid of the Hobbs switches and run a dead headed (the little cheap holleys are the best regulators for nitrous) regulator to the fuel supply on the plate system. Make sure you have unregulated fuel pressure going to the fuel pressure regulator for the plate system. On a few of my buddies cars and on my last race car I just put a T fitting before the regulator going to the carb and used that to supply fuel to the Holley regulator that fed the fuel supply to the nitrous. You do not need a return line from the Holley regulator, just run it dead headed to the plate.

You also need to learn how to flow a fuel system. If you do not know what I mean ask and I will explain it .

What size jets are in the plate?

A 150 shot is a little sneeze, it does not need to be complicated, you have plenty of fuel pump and the 3/8 line is ok, just make sure you do not have a restriction somewhere............

 

69 N.O.X. RATT... Thanks for the reply... I was thinking the same thing that running a small shot like 150 shouldnt have soo many issues! and I am getting frustrated with it at this point.
Now that I think about it, the Hobbs switch before the regulator is going to constantly read 14psi cause thats what the pump puts out... and nothing is regulated till after the regulator, CORRECT? or not?

Either way, Im going to try your suggestion... ordering a cheap Holley 12-803 regulator and run a Tee fitting before the regulator for the carbs
The only fuel filter I am running now is the Earls that I installed today...they claim good for 4-5gpm (240-300gph) and up to 75psi... I cant imagine this should be a restriction..

There are 150Hp jets in there now... I lowered the hobbs way down in psi, in the past and ran 100HP jets and never had a problem

The only thing I can think of "flow a fuel system" is to set the pressures with the fuel solenoid open, but Im not sure if thats waht you mean and even 100% sure how to do it, so please explain sir... Thanks!!

 

Yes, if the Hobbs is before the regulator, it will read what ever the pump is giving it.

Sounds like the fuel filter is good to go, just to be sure make sure there are no other restrictions.

I know the system is set for a 150 shot, but what are the actual sizes of the jets ?

You are right about flowing the sytem, you want to have the fuel supply going through the plate (flowing through an open fuel selinoid), or a fixture with the same size jet that is in the fuel side of the plate. That is your flowing fuel pressure.

 

63 nitrous jet and 71 fuel jet

Ill have to get those new parts, install, and then try doing a flowing fuel pressure setting... ill do away with the hobbs since itll be too close to the solenoid after adding the second regulator.