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Thread: Insignia 2.0 CDTi - engine braking ???

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    Regular Member vxinsigniaboy's Avatar
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    Default Insignia 2.0 CDTi - engine braking ???

    Having my Insignia 2.0 CDTi 130 SRi some 5mths now, although very pleased with car.

    But found the engine is not much good with braking on overrun in 6th, 5th or 4th having to use the brakes more than my previous Citroen Gr Picasso 1.6Hdi in same conditions on motorway etc having to allow greater space although not a bad thing but allows more idiots to jump into gap between me and one in front.

    Are all these like this or need to visit dealer.

    thanks

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    Full Member Big Sig's Avatar
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    Maybe its intentional, would mean you would need less fuel to keep going = saving cash.
    Now I need a turbo to keep up!

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    Regular Member vxinsigniaboy's Avatar
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    thanks,

    but i would save more if the engine would brake to slow down better than using having to use brakes and wear my pads quicker.

    Tha Alfa range using the same engine brakes far better for whatever reason.

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    Full Member GazVXLINE170's Avatar
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    Diesels actually have better engine braking than petrols due to their higher compression ratios.

    The problem with most diesels concerning engine braking is that fact that the gear ratios are very wide. This means that engine braking in 6th is like coasting. If you use engine braking in 1st, 2nd and 3rd (pushing it here lol) it should be mush more effective. Sounds normal to me.
    Insignia VX-Line Nav CDTI 170.

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    Full Member Big Sig's Avatar
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    Quote Originally Posted by Gazza4 View Post
    Diesels actually have better engine braking than petrols due to their higher compression ratios.

    The problem with most diesels concerning engine braking is that fact that the gear ratios are very wide. This means that engine braking in 6th is like coasting. If you use engine braking in 1st, 2nd and 3rd (pushing it here lol) it should be mush more effective. Sounds normal to me.
    Pinched from a well known site:

    Petrol (gasoline) engines

    The term engine braking usually refers to the braking effect caused by throttle position-induced vacuum in petrol (gasoline) engines. While some of the braking force is due to friction in the drive train, this is negligible compared to the effect from vacuum.
    When the throttle is closed, the air flow to the intake manifold is greatly restricted. The concept can be illustrated by the amount of effort required to blow/suck through a thin tube vs. a thicker one. It is the work the engine has to do against this restricted air flow that provides the braking effect.


    Diesel engines

    Diesel engines do not have engine braking in the above sense. Unlike petrol engines, diesel engines vary fuel flow to control power rather than throttling air intake and maintaining a constant fuel ratio as petrol engines do. As they do not maintain a throttle vacuum, they are not subject to the same engine braking effects.
    However, some alternative mechanisms which diesel engines use that replace or simulate real engine braking include:
    A compression release brake/'Jake-brake' - This is the type of brake most confused with real engine braking; It is used mainly in large diesel trucks and works by opening the exhaust valves at the top of the compression stroke, resulting in adiabatic expansion of the compressed air, so the large amount of energy stored in it is not returned to the crankshaft, but is released into the atmosphere.
    Normally during the compression stroke, the compressed air would act as a spring and push back the cylinder (Which is why normal diesel engines don't have any engine braking), but with a jake brake, the compressed air is released (with a loud pop). Without the compressed air to spring back the cylinder, the engine must continue to do work to pull the piston back down, so the engine loses the energy from that compressed air charge.
    This type of brake is banned or restricted in many locations as it creates a sound similar to automatic gunfire, although not as loud; It is very effective however, and creates immense amounts of braking force which significantly extends friction brake life. A 565 hp (421 kW) diesel engine can produce up to 600 hp (450 kW) of braking power.[citation needed]
    An exhaust brake - This works by causing a restriction in the exhaust, much like the intake throttle causes in a gasoline engine. In simple terms, it works by increasing the back-pressure of the exhaust. Nearly all of these brakes are butterfly valves similar to a throttle valve, mounted downstream of the turbocharger if there is one.
    A mechanism related to the exhaust brake is back-pressure from a turbocharger. In turbodiesels with variable-vane turbos, the vanes will close when the accelerator is released, which creates a back-pressure braking effect similar to an exhaust brake. Even fixed turbos, especially larger ones, will cause some back-pressure when they are below the turbo threshold (albeit not to the same extent as a variable turbo) and contribute to the braking effect.
    Now I need a turbo to keep up!

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    Ex Vec-C Admin Stevel's Avatar
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    I don't know about the 130 but my 160 Insignia is no different to the 150 Vectra in terms of engine braking or any similar diesel I've driven. I haven't driven a Citreon though.

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    Full Member GazVXLINE170's Avatar
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    Quote Originally Posted by Big Sig View Post
    Pinched from a well known site:

    Petrol (gasoline) engines

    The term engine braking usually refers to the braking effect caused by throttle position-induced vacuum in petrol (gasoline) engines. While some of the braking force is due to friction in the drive train, this is negligible compared to the effect from vacuum.
    When the throttle is closed, the air flow to the intake manifold is greatly restricted. The concept can be illustrated by the amount of effort required to blow/suck through a thin tube vs. a thicker one. It is the work the engine has to do against this restricted air flow that provides the braking effect.

    Diesel engines

    Diesel engines do not have engine braking in the above sense. Unlike petrol engines, diesel engines vary fuel flow to control power rather than throttling air intake and maintaining a constant fuel ratio as petrol engines do. As they do not maintain a throttle vacuum, they are not subject to the same engine braking effects.
    However, some alternative mechanisms which diesel engines use that replace or simulate real engine braking include:
    A compression release brake/'Jake-brake' - This is the type of brake most confused with real engine braking; It is used mainly in large diesel trucks and works by opening the exhaust valves at the top of the compression stroke, resulting in adiabatic expansion of the compressed air, so the large amount of energy stored in it is not returned to the crankshaft, but is released into the atmosphere.
    Normally during the compression stroke, the compressed air would act as a spring and push back the cylinder (Which is why normal diesel engines don't have any engine braking), but with a jake brake, the compressed air is released (with a loud pop). Without the compressed air to spring back the cylinder, the engine must continue to do work to pull the piston back down, so the engine loses the energy from that compressed air charge.
    This type of brake is banned or restricted in many locations as it creates a sound similar to automatic gunfire, although not as loud; It is very effective however, and creates immense amounts of braking force which significantly extends friction brake life. A 565 hp (421 kW) diesel engine can produce up to 600 hp (450 kW) of braking power.[citation needed]
    An exhaust brake - This works by causing a restriction in the exhaust, much like the intake throttle causes in a gasoline engine. In simple terms, it works by increasing the back-pressure of the exhaust. Nearly all of these brakes are butterfly valves similar to a throttle valve, mounted downstream of the turbocharger if there is one.
    A mechanism related to the exhaust brake is back-pressure from a turbocharger. In turbodiesels with variable-vane turbos, the vanes will close when the accelerator is released, which creates a back-pressure braking effect similar to an exhaust brake. Even fixed turbos, especially larger ones, will cause some back-pressure when they are below the turbo threshold (albeit not to the same extent as a variable turbo) and contribute to the braking effect.
    Why not quote everyone else who uses the term?
    Insignia VX-Line Nav CDTI 170.

  8. #8
    Regular Member vxinsigniaboy's Avatar
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    Quote Originally Posted by Big Sig View Post
    Pinched from a well known site:

    Petrol (gasoline) engines

    The term engine braking usually refers to the braking effect caused by throttle position-induced vacuum in petrol (gasoline) engines. While some of the braking force is due to friction in the drive train, this is negligible compared to the effect from vacuum.
    When the throttle is closed, the air flow to the intake manifold is greatly restricted. The concept can be illustrated by the amount of effort required to blow/suck through a thin tube vs. a thicker one. It is the work the engine has to do against this restricted air flow that provides the braking effect.

    Diesel engines

    Diesel engines do not have engine braking in the above sense. Unlike petrol engines, diesel engines vary fuel flow to control power rather than throttling air intake and maintaining a constant fuel ratio as petrol engines do. As they do not maintain a throttle vacuum, they are not subject to the same engine braking effects.
    However, some alternative mechanisms which diesel engines use that replace or simulate real engine braking include:
    A compression release brake/'Jake-brake' - This is the type of brake most confused with real engine braking; It is used mainly in large diesel trucks and works by opening the exhaust valves at the top of the compression stroke, resulting in adiabatic expansion of the compressed air, so the large amount of energy stored in it is not returned to the crankshaft, but is released into the atmosphere.
    Normally during the compression stroke, the compressed air would act as a spring and push back the cylinder (Which is why normal diesel engines don't have any engine braking), but with a jake brake, the compressed air is released (with a loud pop). Without the compressed air to spring back the cylinder, the engine must continue to do work to pull the piston back down, so the engine loses the energy from that compressed air charge.
    This type of brake is banned or restricted in many locations as it creates a sound similar to automatic gunfire, although not as loud; It is very effective however, and creates immense amounts of braking force which significantly extends friction brake life. A 565 hp (421 kW) diesel engine can produce up to 600 hp (450 kW) of braking power.[citation needed]
    An exhaust brake - This works by causing a restriction in the exhaust, much like the intake throttle causes in a gasoline engine. In simple terms, it works by increasing the back-pressure of the exhaust. Nearly all of these brakes are butterfly valves similar to a throttle valve, mounted downstream of the turbocharger if there is one.
    A mechanism related to the exhaust brake is back-pressure from a turbocharger. In turbodiesels with variable-vane turbos, the vanes will close when the accelerator is released, which creates a back-pressure braking effect similar to an exhaust brake. Even fixed turbos, especially larger ones, will cause some back-pressure when they are below the turbo threshold (albeit not to the same extent as a variable turbo) and contribute to the braking effect.
    Yeah for big truck diesels,

    But I've had diesels (pre ECU)for approx 19yrs of different makes. When you overrun in 3rd, 4th or 5th they had a good overrun braking effect down hill, knowing these models have 6th and I'm not worrying about that because of its high gearing. But todays ECU controlled engines, some are like an engine that is worn and has no compression. As said earlier the Alfa and Saab use the same engine although different outputs are better with the overrun breaking effect.
    And my last car a Citroen C4 Grand Picasso 1.6 HDi (7 seater) and my wifes Peugeot 307 2.0 Hdi are far better slowing down on overrun.

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