Another Sniper build tread

Discussion in 'High Tech for Old Iron' started by Trond-Jarle Pedersen, Jan 13, 2021.

  1. Trond-Jarle Pedersen

    Trond-Jarle Pedersen Active Member

    New Delphi coolant sensor mounted to replace the Holley supplied.

    Coolant and intake manifold temp now matches perfectly.
  2. Trond-Jarle Pedersen

    Trond-Jarle Pedersen Active Member

    Fuel pressure stability...

    I did notice that the fuel pressure gauge was vibrating, and looking at the Holley forums I see that this is a common occurrence for those that are running the system dead-headed with the regulator in the tank (or near the tank)

    That kind of makes sense to me since there will be a delay from the injectors opening until the pressure at the regulator have fallen sufficient for it to open and react.
    In addition I am using hardline with ~6 inches of rubber fuel lines which makes the system more rigid and can therefore increase the instability.

    So I hooked up the scope with a pressure transducer connected to the fuel pressure port.

    Fired the car up and this is what I see:

    (did not calibrate the transducer, so the total pressure is slightly off, it is 60psi and not 68psi)

    Idle car in neutral (so low fuel consumption)
    Fuel pressure fluctuates with ~5psi as injectors are opening

    1200rpm car in drive, (to add a bit of load to the engine)
    Fuel pressure not stable, and 10psi ripple...
    So between 53 and 63psi true fuel pressure, very sensitive to load...

    I then blipped the throttle, from idle to ~1000rpm and down to idle with the car in drive:

    I added a fuel pulse dampener from Radium Engineering and did the same test:

    still some minor ripple but quite a bit more stable

    1200rpm, car in drive:
    Quite a bit better, 4Psi ripple

    No scope plot of blipping the throttle, but did test that and I could not see any additional ripple.

    Now: Is the fuel pressure ripple an issue?
    Most likely not, since the system woupd able to tune as it _should_ be systematic for a given load/tps/rpm.
    However I would think it gets a bit worse at full load, but perhaps not since as the required fuel is increased the regulator duty-cycle is increased until it is open most of the time reducing the pressure drop...

    I also think that if one is using hardlines it will be more ripple than those that are running hoses since those have some "give" and will to some extent act as a pulse damper in them self...
    Last edited: Feb 22, 2021 at 3:50 PM

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