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Some basics about performance tuning - by Drifter

Discussion in 'Engine and Drivetrain' started by drifter, Mar 22, 2011.

  1. drifter

    drifter Regolare

    Messages:
    310
    London/Mumbai
    I am starting this post because I am fed up with the rubbish I read in different forums regarding certain performance tuning measures. I will develop this thread slowly as it is a lot of work and will try to keep it to Fiats, but most of it will be applicable to other brands as well.

    It all started with a fuel pressure regulator. Some ruthless sellers of performance items (I am not calling them performance tuners as the are at best performance bodgers) try to sell fuel pressure regulators as the best thing since sliced bread. What is the purpose of a fuel pressure regulator? Either to keep the pressure constant or to regulate the pressure to cetain values the ECU can reference to.

    So, why then doesn't do the fuel pump this? Because the purpose of the pump is to supply fuel. The fuel pump is operating at a set pressure, but when plenty of fuel is needed all of a sudden or the engine changes rapidly to low rpm then pressure fluctuations come in that upset the fuel delivery and in due course the ECU has to even out this on top what it is supposed to do. There is some reasons for the need to stabilise or regulate the pressure.

    Also it needs to be remembered that even if the ECU can adjust to fluctuations the lambda sensor sits several strokes behind, which means it is running late after the values and then telling the ECU to intervene.

    To supply the amount of fuel needed in the combustion chamber the ECU relies in the basic program on a set fuel pressure, a set injector size, a fuel pump that delivers a certain amount of fuel and the variable injection duty cycle.

    As most cars run with duty cycles of 60% a good 50% power increase is possible before uprating any of the components for fuel delivery.

    Even the best AIRs will not increase peak power by more than 13%, which is just about the capability of the ECU to adjust the fueling for (the ECU is purposely limited) the extra air.

    Fitting a fuel pressure regulator for this is outright nonsense. This calls only for a re-map to get the best out of the engine.

    A fuel pressure regulator does not increase fuel flow as much as people think.

    If you have a system pressure set at 3.5 bar the increase to 4 bar would only increase the fuel delivery by 7%. Going from 3.5 bar to 5 bar would increase the fuel delivery by 20%. But this is the theory because the fuel pump will not support it to this high a pressure.

    Also it has to be remebered that a lot of the fuel sender units have the pressure regulator in the unit built in. This would require removing the regulator from the tank and altering the sender unit.

    TBC.
  2. R Alavandar

    R Alavandar

    Messages:
    29
    Chennai
    In a common rail system, the function of fuel regulator is only to maintain certain back pressure in the gallery / common rail so that the injector cum fuel pumps of individual cylinders are not starved of fuel at their suction ports.Normal setting by original maker is sufficient to ensure this at all power range. The gallery is served by the fuel lift / priming pump, which delivers typically at about 2 to 3 bar pressure. The injection pumps deliver to cylinders at a very high pressure, typically at 200 bar. Actual time of injection and quantity are determined by the ECU or the engine management programme based on the crank angle sensor,set/actual rpm and other parameters. Based on this, the solenoid valves fitted on individual plunger pumps connect the high pressure injection line to the leak off line and hence the of fuel is stopped due to dropped pressure (ie from 200 bar to 2 to 3 bar due to opening of solenoid valve to connect pressure line to the common rail .Now, it looks absurd to think that by changing or by increasing the pressure regulator setting , which maintains a back pressure of 2 to 3 bar in the common rail will improve the performance of the engine. (I am a marine engineer and am running similar engines of Nogva/ Scania on ships)
  3. drifter

    drifter Regolare

    Messages:
    310
    London/Mumbai
    The above was more pointed towards petrol engines than Diesel engines. However, you are right on the Diesel and your final conclusion is spot on. Unfortunately some so called 'tuners' want to tell different, which is a shame and there is certainly no need to do this.
  4. sungoa2010

    sungoa2010

    Messages:
    2,878
    Goa
    My question is slightly off topic but I want to see any correlation between what you have mentioned above with the following observation. Recently I have observed while suddenly reduced the speed (Punto 1.4 FIRE) from high speed to low speed (~15-20kmh) to avoid a bad road, engine stopped and got a message "check the fuel pressure" or "Low oil pressure". This has not happened before or after the incident.If I remember correctly I had pressed the clutch and the engine should not stop. Is it any way connected to the pressure fluctuations that you were mentioning?
  5. drifter

    drifter Regolare

    Messages:
    310
    London/Mumbai
    This is one incident here it could happen. And in the particular instance the regulator has prevented even more of a fluctuation.

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