Fuel systems...
#21
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Even if the small return line affects fuel pressure by a little and you are running an adjustable fpr and a megasquirt your just going to tune it to the available fuel. Should not make a difference.
#23
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Why? It would consistently add the same resistance and lets hypothetically say it adds 10psi to the fuel, you would never know it but you would set the fuel pressure to 40psi or what ever you want as long as it was above 10psi. It would probably only affect it at all at idle.
I understand its just wrong but sometimes wrong works.
I understand its just wrong but sometimes wrong works.
#24
Why? It would consistently add the same resistance and lets hypothetically say it adds 10psi to the fuel, you would never know it but you would set the fuel pressure to 40psi or what ever you want as long as it was above 10psi. It would probably only affect it at all at idle.
I understand its just wrong but sometimes wrong works.
I understand its just wrong but sometimes wrong works.
--Ian
#25
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The problem is that it's not consistent. You're getting whatever the pump can deliver, and that varies with voltage, temperature, amount of fuel in the tank, and probably a few other things. So you turn the headlights on, system voltage drops by half a volt, and idle fuel pressure goes down by 5 psi (making up these numbers, but you see the point)
--Ian
--Ian
#26
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Would that voltage issue not happen anyway with any return system? A smaller than ideal line would just act as a regulator, its its even a restriction. Regulators are static (except boost reference but not at idle).
#28
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But if you use an intake referenced fuel pressure regulator (i.E. a regulator that keeps the fuel pressure at a certain level ABOVE intake), it would set the Fuel Pressure at the setpoint (IM + FP). The only time when the backpressure from the return line would affect the outcome is when the backpressure is higher than or close to the setpoint.
#34
The variable restriction in the regulator has a mechanical limit on how far it can open and if you hit the limit then the regulator stops being able to adjust the pressure. At that point, any variance in the flow output of the pump will be directly reflected as a change in the pressure in the rail. A return line that is too small for the desired fuel flow will cause pressure to back up into the regulator and put you into this state.
--Ian
#35
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Not cheaper. Just smaller.
Pressure Transducer or Sender 100PSI for Oil Fuel Diesel Gas Air Can'T for Water | eBay
Pressure Transducer or Sender 100PSI for Oil Fuel Diesel Gas Air Can'T for Water | eBay
#36
Why? It would consistently add the same resistance and lets hypothetically say it adds 10psi to the fuel, you would never know it but you would set the fuel pressure to 40psi or what ever you want as long as it was above 10psi. It would probably only affect it at all at idle.
I understand its just wrong but sometimes wrong works.
I understand its just wrong but sometimes wrong works.
#38
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It would work as you described and be ok at idle too, so long as the regulator can open up enough to bypass enough fuel to hit the target PSI at idle. It depends if your regulator can make an adjustment larger than the pressure drop on the return line. My guess is a 5-10 PSI pressure drop on the return line wouldn't be a problem at all on an aftermarket regulator, not sure on the OEM one.
#39
I did some testing yesterday on my new fuel pump setup, a Walbro 450 and a Walbro 255. I have 6AN return line with aftermarket regulator. At idle, I can turn on the 255, then turn on the 450. Fuel pressure stays within 1PSI of target regardless of which pump, or both, are on. Flowing 700 LPH, it's safe to say there's a few PSI pressure drop in that line. Regulator takes care of it.