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How much does the heat affect BHP??

Discussion in 'Other Brands & Models' started by Drystone, Apr 22, 2003.

  1. Drystone
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    Drystone Member

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    [Apr 22, 2003]
    Question for those of you in the know.

    On the rare days when the temperature gets up in the high 20s upwards, what sort of drop in power will a 1.8T engine see?

    I'd like to know because I've convinced myself that my car is noticeably slower when the sun shines. /ubbthreads/images/graemlins/cry.gif /ubbthreads/images/graemlins/wink.gif

    Cheers,

    Christian
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  3. Crafty
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    Crafty Member

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    [Apr 22, 2003]
    gte turbo ? oooh. LET conversion ?
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  4. RAPS3
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    RAPS3 Well-Known Member

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    [Apr 22, 2003]
    Yeah, it was a in the garage have a go bloody knuckles conversion. The things you do. I've needed another turbo'd car to play with ever since hence the S3.
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  5. amoffat
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    amoffat Member

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    [Apr 23, 2003]
    I'm not sure that the heat really does affect the performance that much, until the engine is really hot?

    At Santa Pod last year, it was about 25C all day, this year it was more like 14/15C and my time was nearly the same, a little better, but I put that down to the engine being looser?
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  6. S3Bangs
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    S3Bangs Member

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    [Apr 23, 2003]
    Hi all,

    I'd like to say that even though Im not mechanically techie minded like most of you seem to be on here (I know how to build houses tho /ubbthreads/images/graemlins/groovy.gif) I have noticed that my car performs best early in the mornings when the air is pretty moist and temperature is say about 2degrees.. I dont know how to explain it but... the cars more urgent, responsive and even sounds better... but come hign noon and the sun... its a completely different story..

    I remember coming back from somewhere a few weeks ago, was about 4am in the morn, right conditions and as I was blatting it along, I even mentioned to my friend in the passengers seat that the car was at its peak perfomance mode... he told me he didnt understand what I meant of which I said to him... the car feels perfect right now but performs less impressively when the temperatures a bit higher
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  7. RichA3Turbo
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    RichA3Turbo ...Watching you! Staff Member Moderator

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    [Apr 23, 2003]
    [ QUOTE ]
    S3Bangs said:
    Hi all,

    I'd like to say that even though Im not mechanically techie minded like most of you seem to be on here (I know how to build houses tho /ubbthreads/images/graemlins/groovy.gif) I have noticed that my car performs best early in the mornings when the air is pretty moist and temperature is say about 2degrees.. I dont know how to explain it but... the cars more urgent, responsive and even sounds better... but come hign noon and the sun... its a completely different story..

    I remember coming back from somewhere a few weeks ago, was about 4am in the morn, right conditions and as I was blatting it along, I even mentioned to my friend in the passengers seat that the car was at its peak perfomance mode... he told me he didnt understand what I meant of which I said to him... the car feels perfect right now but performs less impressively when the temperatures a bit higher

    [/ QUOTE ]

    When there is moisture in the air and its quote cool, its like using water injection... just alot less effective. moist air is more dense.

    Rich
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  8. wigginer
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    wigginer Member

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    [Apr 23, 2003]
    I picked this segment up on Google ... bit techie in places but gets the point across:

    "Cold Air:
    Feeding cool air to an engine will increase the power output. Increasing inlet pressure will also increase the power (hence forced induction such as superchargers and turbos). The reason for this is that the engine power depends upon the mass flow rate of air into the engine. Higher pressure and cooler air will be more dense and will be pushed into the engine harder.

    The air mass flow rate is proportional to pressure/square root of temperature

    This means that doubling the inlet pressure from 1 bar (atmospheric pressure) to 2 bar would theoretically double the power.

    Reducing the air temperature from t1 (in degrees C) to t2 (C) would increase power by the square root of ( (273+t1)/(273+t2) ). The 273 is used to convert from deg C to deg Kelvin (absolute temperature units, 0 Kelvin which is -273 deg C is absolute zero, below which you can't go). Eg: going from 35C to 15C, power increase is square root of ( (273+35)/(273+15) ), ie square root of (308/288) = 1.034, or 3.4%.

    A rule of thumb is 1% power and torque increase for each 5.5C of temperature drop.
    This is 1% power for each 10F because an increase of 1C would be increase of 1.8F.

    If you want to estimate the power increase for pressure boost then things are a bit more ticky. The theory so far would give a 100% rise per 1 bar, which is 6.9% per psi, since there are 14.5 psi per bar. However, the compression process will raise the air temperature. This will make the air less dense and thus reduce power. The risk of detonation (pinking/knocking)will also be increased. Cooling the high pressure air with an intercooler or charge cooler is the way round this. There will be a pressure loss across the cooler though."

    This segment raised another question for me. If ambient air temperature drops as you climb above Sea Level, then does this mean BHP increases with height? The answers in there somewhere ...
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  9. RichA3Turbo
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    RichA3Turbo ...Watching you! Staff Member Moderator

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    [Apr 24, 2003]
    [ QUOTE ]
    that wigginer said:
    This segment raised another question for me. If ambient air temperature drops as you climb above Sea Level, then does this mean BHP increases with height? The answers in there somewhere ...


    [/ QUOTE ]

    No it wont, because the higher you go, the less dense the air. There would be a certain height where the + and - cancel each other out.

    Rich
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  10. Administrators
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    [Apr 24, 2003]
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  11. wigginer
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    wigginer Member

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    [Apr 25, 2003]
    [ QUOTE ]
    RichA3Turbo said:No it wont, because the higher you go, the less dense the air. There would be a certain height where the + and -
    [ QUOTE ]
    that wigginer said:Agree ... Now I think about it, the reason the temperature reduces is because of the increase in height ... rarified atmosphere and all that ! ... therefore the cancellation of the effect.
    This segment raised another question for me. If ambient air temperature drops as you climb above Sea Level, then does this mean BHP increases with height? The answers in there somewhere ...


    [/ QUOTE ]

    No it wont, because the higher you go, the less dense the air. There would be a certain height where the + and - cancel each other out.

    Rich

    [/ QUOTE ]
    #10

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