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Old 05-16-2005, 09:21 PM   #1
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Nitrous; Fuel pressure switch, what PSI?

Well, I'm looking to piece togeather some saftey componets for the nitrous system I haven't bought yet :) I'm just wondering how low can the fuel pressure go before bad things start to happen? I'm thinkin ~40 psi but... I really have no idea.

Thanks for any info,

Matt


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Old 05-19-2005, 04:01 PM   #2
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It depends on what size fuel jets you have. If you have bigger jets than you need for 39 psi, then you should be safe down a little lower. If I were you I would try to find a way to get fuel to the nitrous at a steady pressure, then you can tune the fuel injectors to compensate for other things to keep your afr where you need it. Then you could find a pressure switch for a little under what you have at the selenoid for back up.
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Old 05-19-2005, 08:43 PM   #3
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Thanks for the reply!

I realise I can re-jet the fuel side of the fogger nozzle for what ever pressure I end up getting at WOT when spraying, what I'm worried about is the rest of the stock fueling system. What pressure do the stock injectors need to work properly at WOT? I guess another question would be, does the ECU run the fuel pump at full-bore when at WOT? If it did that would make things easier.

What I'm trying to do is spray a 75 shot as safely as possible without having to spend a bunch of money on a custom nitrous tune. The idea is to get a mail order SCT tune with say a 87oct tune, 91/94 oct tune, -4 deg spark from stock/87 oct tune , -6? deg spark or more tune (for a bigger shot one day). Get some colder plugs.... a box of different fuel jets along with an EFI nitrous kit and if there's enough fuel for everything, (pressure switch stays on if I figure out what PSI I need) fine tune the setup by reading plugs and changeing/drilling fuel jets. Hey that works for carburated cars, it should work here right? It wont be as efficient as it could be but it would/should be safe.

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Old 05-19-2005, 10:15 PM   #4
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my car idles at 30-35 psi fuel pressure. at wot it's 40ish. i haven't sprayed since i got the new gauges, but i'd guess it drops a bit when you open the solenoids. i'd say 35 psi for the switch, if it goes below idle pressure i wouldnt want to spray. i won't ever rob from the fuel rail again, for a 75 shot it may still be ok, i did it for a year with no problem.

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Old 05-19-2005, 10:24 PM   #5
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use a nitrous cutoff saftey switch,i have used the complete nx kit on my sunfire never had a problem but it is always wise to invest in the switch and also a bottle heater for the perfect mix,best thing is for you too do is call nx express these guys are awesome they will tell you everything about nitrous and all of the myths assoiciated with it as well.you shouldnt really need a tune with some of these systems out there too,colder plugs,higher octane good flowing exhaust and intake,should make thing smooth.by the way i sprayed a 50 shot on my sunfire alot and put 28,000 miles on it with it installed no problems except towards the end of my ownership and spraying the clutch would start slipping.best to invest in a heavy duty clutch as well in the near future.
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Old 05-20-2005, 01:10 AM   #6
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Thanks guys, good stuff.

The stock pump should be able to supply a 100 shot without a prob. It's just getting the fuel from the pump to the fuel rail and fogger nozzle through all that itty bitty fuel line. I wonder if there's a way to tee into the fuel system at the pump and run a dedicated line for the nitrous system... hmmm

Ah well I'll worry about that later, I'm sure a 50 and 75 shot will be more than enough fun for a while.
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Old 05-20-2005, 06:43 AM   #7
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75 is a great shot on the focus, real kick in the pants. i wouldn't try 100 without stronger rods and timing. tapping into the fuel rail is the same as tapping into the line. the fuel pressure is controlled by throttle position, it kicks up to 40 when you hit the gas. my problem with robbing from the rail is volume. i don't believe the pump can keep up when you instantly put another outlet in there, basically 5 instead of 4. ya know? I'm running a standalone fuel system for the nitrous. little cel with higher octane gas, new pump and regulator. that way the stock fuel rail and pressure is not affected.

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Old 05-20-2005, 07:24 AM   #8
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Quote:
Originally posted by mr.squatch
the fuel pressure is controlled by throttle position,
The fuel PSI is controlled by the fuel rail PSI sensor and the duty cycle that is set in the PID for the fuel pump controller as well as the target fuel PSI in the PCM

The only way to raise the fuel PSI is with a chip , Anything over a 50shot will cost you an engine with out higher octane or timing removed with a chip

Tom
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Old 05-20-2005, 08:08 PM   #9
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Ok, I'll stick to a 75 shot at most, I don't want to dive into the engine right now.

As for tapping into the fuel rail or line, it would depend on where in the line I tapped into. If I ran a second line directly from the pump I would be able to move twice the volume at the same pressure provided the pump could supply it... but that's probably more effort than it's worth.
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