Do cars lose BHP over time + remap question - Page 4

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    #31
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    Fuel wise, if you're running "good quality" fuel to protect the engine all well and good.

    One thing I would say though (which is possibly less true of newer engines with knock sensors) is run the fuel the car was tuned while running.

    I've come across people before getting cars rolling road mapped and then saying "and now I'll see how it goes on higher octane fuel"

    The answer to the above is slower!


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    #32
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    Quote Originally Posted by E36Coupe328 View Post
    I've come across people before getting cars rolling road mapped and then saying "and now I'll see how it goes on higher octane fuel"

    The answer to the above is slower!
    Can you explain why please ?
    Z3
     
     

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    #33
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    You running the M52TUB25 engine?
    I can happily say that mine has been RR'd (at 146,000 miles) at 180bhp 181lb/ft torque.
    Same engine in mine, i believe. Thats standard. No mods whatsoever.
    So, after 11 years and a lot of miles, i'd say no, that it doesnt lose much in the way of horses, but as with any mechanical pump, you gotta look after it...mine is cosseted, but it gets used. (brands hatch in the first week of ownership always shows up the weak points..)
     
     

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    #34
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    Quote Originally Posted by markrnorton View Post
    Can you explain why please ?
    I could, but waiting for one of the tuners to jump on it.


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    #35
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    One thing that people have to understand is that the octane number isn't the amount of octane present, it's the ratio of octane to heptane that provides a similar knock resistance.

    Knocking or detonation occurs when the temperatures and pressures inside the cylinder get too high and part of the fuel mix auto-ignites, this then starts off a chain reaction where the shockwave of the ignited fuel sets off the fuel near to it, and it passes through the mix at the speed of sound burning everything.

    Normal combustion is "deflagration" where a flame front passes through the mix in a controlled manner.

    This is burning things by passing heat onto the nearest cool neighbours. With detonation, the remaining mix is just under the auto ignition temperature, and the shockwave pressure is enough to tip it the final amount.

    If you lit the corner of a piece of paper, it would deflagrate by the flame slowly incresing in size and spreading.
    Detonation of paper would be when the sheet burns from one side to the other at supersonic speed.

    Back to the fuels, higher "octane rating" fuels can resist the pressures and temperatures better, which allows you to advance the ignition, and start the burn earlier.

    The faster an engine turns, the less time you have to extract power out of the expending gasses. The speed at which they burn doesn't change much and you need to get the pressure up nice and high for when the piston is at between 13-16 degrees of crank rotation.

    This can be thought of like pedalling a bike, if you push hard when the pedal is pointing directly up, you'll just balance and sit on the top.
    The best leverage you'd get on a pedal would be when it's at 3 o'clock, but as it's a drawn out push, rather then a quick bang, you get the most useful "work" done when you aim for peak pressures around 14-ish degrees.


    The spark will occur before the piston has even reached the top of the cylinder in preparation to get this peak pressure in the right spot, and the faster the engine turns, the earlier you need to start the burn to get it to land on the sweet spot.

    When the octane rating is increased, you can start the burn earlier without fear of the mix exploding by itself when the pressures get high, and one way to increase the octane rating is to slow the speed of the burning

    Aside from increasing the amounts of harder the ignite components in fuel, you can also get a couple more octane points by slowing the burn instead, and it's this slowing that can reduce power.

    Most petrol fuels are blended in such a way to keep the flame front moving at the same speed, although there is quite a few places out on the net that are under the impression that octane number is directly proportional flame front speed.

    There are infact some racing fuel blends that have very high octane numbers, and high flame front speeds.
     
     

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    #36
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    Well put.

    Bassically if you tune a car with one fuel octane rating, then run it on a higher octane fuel, all things being equal the mixture will be being lit too late, effectively behaving as if ignition is too retarded and hence slower


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    All my cars runs better on shell fuel. Second choice would be bp but mainly shell I use. I get slightly more power from using it compared to other petrol stations. Also my engines seem to last longer using shell fuels.
    I own these 2 cars
    Bmw 520i se 2.0 24v straight 6 1992
    Proton wira 1.5 12v se 2002

     
     

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    #38
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    Quote Originally Posted by Welshy_Pete View Post
    Also my engines seem to last longer using shell fuels.
    If you mostly use Shell how can you tell?


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    hi
    (1)do you need to put high octane fuel in for a a bmw 320i 170bhp tre-map?
     
     

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    #40
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    Not usually unless it is pushed to the absolute max
     
     

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