Vacuum referenced FPR tuning questions...
09-02-2009, 02:49 PM
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Vacuum referenced FPR tuning questions... Hello,
I have an adjustable fuel pressure regulator on my LS6. I currently have the manifold reference port capped... my fuel pressure is fixed.
I have been considering moving to a manifold vaccuum referenced configuration for a few reasons...
1- longer injector pulsewidth at hagh manifold vacuum situations like idle. Should help idle with a larger fuel injector.
2-Easier adjustment of the injector ofset vs volts vs kpa table.. (if I need to change injectors)the table would vary by voltage only, not by kpa as the pressure differential across the injector is the same at any state of engine vaccuum.
3-The fuel pump would have an easier life as the line pressure against would be reduced in all light load situations.
These are all good things in my opinon. One concern I have is about the speed of the rail pressure change. With the fixed pressure/non vacuum referenced setup, the computer makes pulsewidth and ofset changes quickly based on the information from the map sensor. Both of these functions would move to the pressure regulator. Will there be some latency in the fuel rail pressure changes under quick changes in throttle position? If I'm cruising along at 40kpa vacuum and floor it, the the manifold pressure drops to 0kpa and the fuel rail pressure has to increase 5.8psi from 52.2 to 58psi for example. Would the delay in "pumping" up the rail 5.8 psi be significant? I would hate to have a stumble while the pressure regulator responded to the map change and then increased the fuel pressure.
What are your thoughts? Has anyone changed back to a fixed pressure setup after having been vacuum referenced for this reason? Feel free to enlighten me on any other considerations that I'm missing.
Thanks in advance,
Bryan
I have an adjustable fuel pressure regulator on my LS6. I currently have the manifold reference port capped... my fuel pressure is fixed.
I have been considering moving to a manifold vaccuum referenced configuration for a few reasons...
1- longer injector pulsewidth at hagh manifold vacuum situations like idle. Should help idle with a larger fuel injector.
2-Easier adjustment of the injector ofset vs volts vs kpa table.. (if I need to change injectors)the table would vary by voltage only, not by kpa as the pressure differential across the injector is the same at any state of engine vaccuum.
3-The fuel pump would have an easier life as the line pressure against would be reduced in all light load situations.
These are all good things in my opinon. One concern I have is about the speed of the rail pressure change. With the fixed pressure/non vacuum referenced setup, the computer makes pulsewidth and ofset changes quickly based on the information from the map sensor. Both of these functions would move to the pressure regulator. Will there be some latency in the fuel rail pressure changes under quick changes in throttle position? If I'm cruising along at 40kpa vacuum and floor it, the the manifold pressure drops to 0kpa and the fuel rail pressure has to increase 5.8psi from 52.2 to 58psi for example. Would the delay in "pumping" up the rail 5.8 psi be significant? I would hate to have a stumble while the pressure regulator responded to the map change and then increased the fuel pressure.
What are your thoughts? Has anyone changed back to a fixed pressure setup after having been vacuum referenced for this reason? Feel free to enlighten me on any other considerations that I'm missing.
Thanks in advance,
Bryan
