I want to setup a regulated return line to keep my fuel from heating up too much. Will this work for me? I attached a (crude) diagram.

 

If you have a 5.5 psi regulator on the main line... wouldn't that mean you only get 1.5 PSI to your Q-Jet ? I think it needs quite a bit more than that. And especially with running N20 you REALLY dont wanna run low on fuel bud. I would run a "return style" regulator that will just return the excess fuel to the tank, WHILE keeping the required pressue at whatever you set it at.

 

The only way this would work properly is if the reg keeps 5.5 psi on its inlet (functioning as a relief valve). Otherwise, you will have zero pressure at the carb.

Most regs operate based on the pressure on the outlet. Make sure you get one that is operating on its inlet pressure as depicted in your diagram. Doing it that way would make the system work properly.

 

If you plumbed a holley regulator there but backwards,
it should function. The amount of nitrous/fuel you could flow
before the saftey switch cut in would be limited.
Should be ok on a 100 hp setting. I would flow the whole system at max demand to be sure. I'd much rather see you use a separate independent fuel line and a pump from the tank to the NOS. fuel solenoid. Experience has taught me and others that this is the best way to go on all but the smallest systems.
A inexpensive carter electric pump will flow more than enough fuel to support a 250hp boost through a 3/8 line with a holley regulator. I know 'cause I already flowed such a system for my car.

Your system would function, but may get into trouble on a real hot day with vapour lock which could be a cotastraphy.
Not worth it In my opinion.
You'd have to flow the required NOS/fuel into a container of some sort ,, while either running on a dyno or down the track at max engine fuel flow (high rpm peak hp) to test out your system without risking the motor. Get the 9psi pump at any rate.
The return line must enter the tank BELOW fuel level to avoid
arriating the fuel to much in the tank,which tends to mess it up.

I'm sure Five7Kid will back me up when I tell ya that the strip is a cruel environment for fuel systems.

 

On this type of system the feed side to the mechanical pump is critical Must have no under sized fittings, rubber hoses that
can heat up and collapse, no sharp right angle elbow fittings
that are exposed to heat. Any reductions in feed line cross sectional area or severe flow turbulance through a fitting/ or joint
could result in a vapour lock from heat. Carfull fuel line routing
and or insulating is nessessary.

At the drags on a hot summer day you tend to sit in the stageing lanes heating up, more than you run so heat management is a real issue.

 

One note:
Only wire the NOS nitrous solenoid to be cut out by the saftey switch if the fuel pressure drops below your predeturmined
safe pressure level. In an event of a "shut down" the extra fuel from the plate won't hurt any thing if it stays on momentarily till you can get "off the button". This would prevent the system from possible "Hunting" while the fuel regulator is reacting to you engaging the NOS system. Just a thought...

Good Luck to ya

 

I hooked it up that way before I had a chance to read all the post. It held fuel pressure but the needle jumped like crazy! I have a crappy (autozone) regualtor but your saying if I reverse it, it may work better? The return line is stock so it goes back into the tank whereever GM decided to put it. I was running both soleniods off the the saftey switch with the idea that it would cut off both and build back fuel pressure and when it was safe automatically come back on for me. Is this not a safe way to do it?

 

I've never seem an AutoZone regulator. But I'll tell you
Crappy won't cut it when it comes to nitrous.
Unless you like replaceing motors. Use a high capacity
regulator like a holley. If you plumb it in reverse in the return line
it will function as a bypass regulator. The return line has to be at least as big as the feed line because it must return all but a small part of the fuel to the tank, at idle (low fuel demand)

 

I reversed it and it does not bleed off any pressure at all no matter what I set it to. It is always at 7.5 psi witch is too high I think for a quadrajet but it seems to be working ok though. My Nitrous kit calls for 5.5 to 6.5 psi so that makes it too rich. Plus I normally dont have my bottle warmed up so its not up to pressure making matters worse. If I abaondon the return and just use the regulator it is supposed to go to 5.5 which would put me right at the bottom of the limit but I am only getting 5 psi. But my bottle pressure is normally low so that might put me right where I need to be and the manufacture normally suggest a rich tune to begin with. (I also have an O2 sensor and gauge I need to hook up still that should help with tuning). Back to the return line think the way I origanally hooked it up it did regulate fuel pressure and return fuel back to the tank when I adjusted the regulator but the needle was soo jumpy on the gauge it was difficult to read. I'm guessing it did that because the pump is machanical and not electric so it pulsates the fuel more. My return line is smaller than the feed line so Im screwed there. I dont want to spend a bunch of money and dont want to screw up my motor either. The safty switch should keep me from doing serious damage I hope!

 

I have been using the 50 hp N2O shot with no problems so far.

 

You may not need a regulator at all. Get a fuel pressure gauge hooked up so that you can observe it while driving.
Duct tape it to the windshield if nessessary.

Remove the regulator and return line from your system. Test the car at full throttle/ high rpm and note the fuel pressure on the gauge. It must maintain 5/6 psi. If it does this while
testing "on the motor" at full throttle /high rpm,you can now test it while injecting the NOS
fuel * without nitrous* Keep the bottle closed.
Repeat the same full throttle/high rpm test but this time
inject the fuel without the NOS (bottle closed) for short burst. Watch the gauge.
If it will maintain 5/6 psi during injection at the power level you choose (NOS/fuel jetting). Then you don't need a regulator.
If the fuel pressure drops below 5 psi at any point, you need more fuel capacity and should go to a separate fuel line and
pump for the NOS. If your static pressure is 7.5 psi or less you
should be ok and you can remove the regulator.