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Old 05-25-2007, 10:07 PM
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Nitrous fuel supply ???

Im having a problem with my fuel supply on my N20 solenoid. I have a 388 approx 450+ hp with a 100 shot plate kit on it. I have a pressure safety switch in my fuel line just before the fuel solenoid. Im running the engine with a maniacal fuel pump. Its a very big pump! Holley 130 gph with a regulator set @ 7.5 psi. I used a test light to confirm that my switch was going open under WOT with nitrous armed. System would come on for less than 2 seconds and cut off. When Im just on motor the switch will remain closed under WOT. New tank, 3/8 lines and tank unit. This is the second pump, same problem, this pump just keeps the pressure up a little longer before switch opens. Car runs 11.80s on motor. According to NOS requirements I don't even need a pump upgrade for 100 shot. And my 130 gph Holley produces more fuel output than a blue pump. But thats volume, I don't know if the pressure would be the same on a blue pump or not under WOT. I hate the noise of an elec pump. Is my switch mounted in the wrong place? Do I need to move it to before the regulator? Or is there no choice but an electric pump? NOS website has zilch on this subject. Thanks.....

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Old 05-26-2007, 12:04 AM
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Volume without pressure is useless.
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Old 05-26-2007, 07:50 AM
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temporaly mount a fuel pressure gauge that you can see from in side the car and go try it and see what that gauge does. This will tell you if the pressure is dropping or you have a bad switch.
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Old 05-26-2007, 08:17 AM
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It sounds like you have plenty of fuel pump there, the problem is probably with the fuel pressure safety switch being set at a higher pressure than what your system requires, like for an injected car application perhaps? You can test this by just putting a jumper across the 2 terminals on the switch and trying it again. If it stays activated you'll know where the gremlin is I dumped my fpss years ago after trying to get it to work reliably for several weekends, IMO a filter on the nitrous feed line is a neccissity tho',,,

Hope that helps
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Old 05-26-2007, 09:49 AM
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The pressure switch should have a small rubber cover in the center of it. They can and need to be fine tuned. In your nitrous instructions it should have mentioned this as well as what the preset was on the switch.

Running though for 2 seconds and then opening tells me you have a fuel pressure drop and as mentioned prior, you need to install a gauge to see what is happening. My guess is your current fuel line is too small.
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Old 05-26-2007, 11:35 AM
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Ya need to get beyond your fear/lothing of electric fuel pumps.
A Carter 4594 7psi 72 GPH pump is good for at least a 250-300 hp shot. At the working pressure (5 to 6psi). Under $100. OEM reliability. Low noise when mounted right.
I would install a small 1 to 3 gallon fuel cell (Summit, JAZ) under hood to supply the nitrous plate using this pump and a regulator. That way your not working against G force on launch and exposing the fuel to a lot of heat.

Engine mounted mechanical pumps (with rear mounted fuel tanks) while capable of supplying lots of volume and pressure work well on applications where the G force of acceleration is not too high (boats, circle track, road racing) and tend to not be exposed to heat soak.
Drag racing exposes the mechanical pump and the feed side fuel lines to a lot of heat (while sitting in the stageing lanes and high G force during launch. This causes a pressure actually a partial vacuum drop in the feed side which combined with the heat ( exhaust, engine, pavement) creates in line boiling (vapour lock).
Your carb, with its fuel bowls can get past this momentary fuel starvation cause the bowls store fuel (acts like a capacitor or serge tank) but the nitrous system cannot tolerate a fuel pressure/delivery drop even if momentary.

Some things that will help your mechanical pump work much better.
Get a heat isolating engine mount plate/gasket.
Make the feed side fuel line larger than the pressure side outlet fuel line. Should be 1/2" for an 11sec car.
Move all the fuel lines away from heat . Wrap them if near a heat source.
Consider a front mounted fuel tank.
Use a return style fuel regulator and a fuel return line to the tank that way the fuel pump does not keep bypassing/recycling the same fuel internally overheating it.
Use only a screen filter on the feed side and a high capacity or two high capacity fuel filters on the pressure side near the carb.
You want to avoid any pressure drops in the feed side and the outlet side of the pump. (right angled pipe fittings, cheap fuel filters, restrictive fittings)
Any pressure drop along the flow path to the carb will cause/allow a fuel boiling point especially on hot fuel.
The boiling point of any liquid (water,fuel etc) is determined by the acting pressure. Low pressure= lower boiling point high pressure= high boiling point.
A mechanical pump cannot move bubbles especially in the feed side. Does not take a lot of heat/reduced pressure to get bubbles in the fuel line or at a fuel fitting.
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Old 05-26-2007, 04:29 PM
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Thanks for all the help guys! I will take all this into consideration and figure this out. I m going to install a fuel pressure gauge at my n2o fuel solenoid and see what the psi is under a load. If the pressure is dropping, I will install a separate fuel system for the n20.
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Old 11-11-2007, 10:30 AM
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same problem

I have about the same setup. I think what is happening is one of two things. The presure will drop for a few seconds when the o2 is on then go back up. The other thing is at 6000 rpm the pump will only put out 4.5 psi. What did you do? I would like to go to an electric pump but do not wont it to quit one day. I have looked at the blue pump but it might get to hot on the street. I have also looked at the 125hp but it only puts out 7psi and I have allot of money tied up in a reg and lines, so I don't want to eliminate the reg.
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