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Punto feeling heavy...

Discussion in 'Technical' started by adigabnp, May 28, 2012.

  1. Comparing humans and cars ? Seriously ? I don't think this example is relevant here. I never said they struggle to breathe. What I said was that due to reduced density and hence rarity of oxygen which is sensed by MAF & O2 sensors, the Ecu based on these readings adjusts the fuel map so that the stoichiometric ratio is maintained. The Ecu will try to maintain this ratio in order to keep the performance and emissions optimum.
    The ECU also uses the IAT as intake temperature too plays a crucial role and is a critical parameter.

    I beg to differ with your second contention. The maximum ambient temperature is what, 40-48c in our conditions ? I am dead sure such temperatures are negligible when we talk about metals expanding when subjected to heat. Melting point of most metals,the ones commonly used in automobiles is a good enough testimony to this.
    Also if the metal components expand as to what you are claiming, how would the gaps increase ? Shouldn't they theoretically reduce ? Why would the fuel pumps pumping capability reduce ?

    'It can cause similar problems with multiple components to bring down the overall engine power' --> Care to explain how and why ?

    Could you explain why only turbocharged engines ?
  2. I can feel difference , on hot days my car doesn't have the enthu like it has below 25 degree mark and it likes when I drive in colder whether.
    why you may not feel may be due to VGT? not very sure.
  3. Ravi

    Ravi Staff Member Janitor

    Messages:
    6,001
    Bangalore
    Grande Punto 1.3
    I personally never felt any difference is "performance", however because of full use of AC and heat, the engine does sound more. In colder weather, without AC, it drivers very smoothly.
  4. Pran

    Pran Superiore

    Messages:
    748
    Bangalore
    Grande Punto 1.3
    Loss of power, just give a try, lift your vehicle to see if the tyres are rotating freely, this is something I have been facing for some time and my vehicle is in SC to fix this, brake caliper related issue. Mileage has dropped for me, but not from 18+ in city, man how do you manage that? Its dropped from 14-15 in city to 10-11km/l.

    Regarding thin air and expansions, I don't know how true it is, but I have felt really sluggish behavior on winter mornings at 5-6am in Bangalore, am I the only one with a different experience to sound stupid here??
  5. Was this for a short period of time once you started driving or was it sustained ?
  6. RaviHegde

    RaviHegde Regolare

    Messages:
    299
    Karnataka
    14.62°N 74.85°E
    Grande Punto 1.4
    Practically increase in temperature leads to increase in gap. We have been suggested to warm the stuck lid of a box or bottle to make it easier to open. Lid will hold tighter to the container if higher temperature reduces the gap. But the reality is reverse of it, higher temperature increases the gap. Therefore it becomes easier to remove the lid when it is heated.

    Let us see mathematically what happens. Overall gap between the lid on the outer side and the box/bottle on the inner side is:

    gap = area of outer circle - area of inner circle

    Area of a circle is square function of radius (pi * r^2). Therefore inner circle area increases comparatively less than the outer circle area due to thermal expansion of the material. That means, the area difference (gap) increases when the temperature goes up. There is another factor adding to this problem. Inner circle radius increases less than outer circle radius because radius increase is a linear function. More the radius, more is the expansion. Because of these 2 acting together the gap increase is more than one can imagine.

    A mechanical component is usually made up of sub-components of different materials/alloys. The have different coefficient of expansion. That dramatically increases the gap. Efficiency of components like fuel pump automatically comes down. Fuel density and viscosity reducing at higher temperatures makes the mechanical components like fuel pump perform worse at higher temperature.

    Please see Mass flow sensor - Wikipedia, the free encyclopedia. It clearly states "When a MAF is used in conjunction with an oxygen sensor, the engine's air/fuel ratio can be controlled very accurately." Indeed that is how engines should work. Therefore I believe problem is because of more complex non ECU issues which are difficult to address.

    Compared to ECU it is much more difficult to control the uneven expansion/contraction of mechanical components. Best way for controlling the uneven expansion of mechanical components is using special alloys with very low cofficient of expansion. Alloy with lowest coefficient of expansion may not have all the mechanical properties needed for a component (e.g. it may not have enough compressive strength or it may not be able to withstand friction prevalent in that component etc.) or it may be too expensive for the use. Therefore it may not be so easy to keep the expansion under strict control. So I believe slightly lower engine performance at higher ambient temperatures is a mechanical problem, not ECU issue. Mechanical problems are much more difficult to solve than problems with precisely programmable component like ECU.
  7. adigabnp

    adigabnp Amatore

    Messages:
    65
    BengaLooru
    BengaLooru
    Grande Punto 1.3
    Pran,
    When I brought Punti, I wasn't optimistic about her mileage. Though, some better driving methods have done good to the engine as well as the mileage figures.
    However, when I drive randomly, the mileage drops to 16kmpl! :(
    So, I suppose it all depends on the way we driver her.

    Ravi & others,
    So, do you mean to say that summer is causing the heavyness? :rolleyes:
    I am confused now. :)
  8. Relativity

    Relativity Superiore

    Messages:
    853
    Chennai
    Can the car feel heavy if the air filter is clogged?
  9. RaviHegde

    RaviHegde Regolare

    Messages:
    299
    Karnataka
    14.62°N 74.85°E
    Grande Punto 1.4
    I believe yes, if not all, some cars feel heavier in summer. I have experienced it with V2 Indica. My Punto 1.4 FIRE is not showing this behavior. May be diesel cars are more likely to feel heavy in summer - just a guess.
  10. gurjinder

    gurjinder Staff Member Janitor

    Messages:
    3,989
    Punjab
    Not at all. I travelled 170 km's in the afternoon today. I could find no difference in performance.

    There is no day and night difference that we can feel in travelling in a 45+ degree heat and 0 degree cold day. The minor difference, if any cannot be felt. It might be known if we strap some 20-30 sensors to the engine and log all the data.

    We're talking of a Turbocharged diesel engine!

    Cheers.

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