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  1. #1
    Dennis Moeller's Avatar
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    S3: (FMIC piping) Why 2" on hot side and 2.5" on cold side

    Heya mates...

    Just a quick question, hope you can help me.

    The weekend after this one I'm getting a FMIC fitted. The shop did put together a kit made of a Forge core (same as in Forge's own kit for the S3 8L) and custom pipes, bends and silicone. We then discussed what diameter we should use for the hot and cold side. The shop wanted to use 2.5" all the way on both the hot and cold side. But on so many setup's we studied lately they all (well 90%) use 2" for the hot side and 2.5" for the cold. Why is that? Isn't 2.5" on the hot side better...why the difference in the first place..

    Can somebody explain this for me...

    Thanks in advance!!
    My old car.. Still miss the lil rocket :-)

    Remapped Stage II - Forge FMIC - Dahlb�ck Intake - K&N - DieselGeek ShortShift - Phenolic - Powerflex Dogbone - Rial Daytona Race 8.5x18" ET30 - Forge Tiebars - Bilstein B8 - H&R 25mm - R32 rear ARB - H&R 20mm Spacers - EBC Discs - Red Stuff pads
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  3. #2
    james0808's Avatar
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    Do a google search for Boyles law and all will become clear.

  4. #3
    1animal1's Avatar
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    Boyles law? isn't that something to do with 'always remove excess hair' so as not to become disassociated with society?
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  5. #4
    Dennis Moeller's Avatar
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    Didn't excactly give me anything. In fact I'm more confused now hehe...

    Can someone give me an answer in layman terms, really appriciate it as they want to start building the kit monday...
    My old car.. Still miss the lil rocket :-)

    Remapped Stage II - Forge FMIC - Dahlb�ck Intake - K&N - DieselGeek ShortShift - Phenolic - Powerflex Dogbone - Rial Daytona Race 8.5x18" ET30 - Forge Tiebars - Bilstein B8 - H&R 25mm - R32 rear ARB - H&R 20mm Spacers - EBC Discs - Red Stuff pads
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  6. #5
    1animal1's Avatar
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    Dave i thought the aim was to decrease area outside of the FMIC.... ie bigger pipes mean a bigger surface area that arent having the same cooling effect as the FMIC...therefore creating more lag.... id guess there would be an optimal point where the pipes are too big or too small for inlet and outlet, two seperate forces obviously being pulled/pushed here

    thats my understanding
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  7. #6
    voorhees's Avatar
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    boyles law states increasing pressure decreases the volume of the gas....how does that figure regarding an intercooler?

  8. #7
    Dennis Moeller's Avatar
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    No one who can explain why the difference in pipes on the hot and cold side...?
    Monday at 16.00 I have to decide...

    Cheers
    My old car.. Still miss the lil rocket :-)

    Remapped Stage II - Forge FMIC - Dahlb�ck Intake - K&N - DieselGeek ShortShift - Phenolic - Powerflex Dogbone - Rial Daytona Race 8.5x18" ET30 - Forge Tiebars - Bilstein B8 - H&R 25mm - R32 rear ARB - H&R 20mm Spacers - EBC Discs - Red Stuff pads
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  9. #8
    fingermouse's Avatar
    thats me

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    id guess at the smaller pipe for the hot so the return is in the cooler longer as it has a larger exit, if they were the same then the coolant would pass through quicker.

    but that is just a educated guess not actually worked it out.
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  10. #9
    voorhees's Avatar
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    forge ones are the same size so keep them the same Dennis

  11. #10
    Dennis Moeller's Avatar
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    Quote Originally Posted by voorhees View Post
    forge ones are the same size so keep them the same Dennis
    Yeah I've noticed that. Were using the same core so probably going the same route as Forge. A mate of mine thought that most (smaller) turbos all have 2" outlet so that was the reason. As simple as that?

    Thanks for the answers guys...
    My old car.. Still miss the lil rocket :-)

    Remapped Stage II - Forge FMIC - Dahlb�ck Intake - K&N - DieselGeek ShortShift - Phenolic - Powerflex Dogbone - Rial Daytona Race 8.5x18" ET30 - Forge Tiebars - Bilstein B8 - H&R 25mm - R32 rear ARB - H&R 20mm Spacers - EBC Discs - Red Stuff pads
    ______________________________________________
    NO ONE EVER REALLY DIED

  12. #11
    Shy19s's Avatar
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    I thought the general rule is to keep it free flowing as poss.. wont 2" be abit restrictive pressure wise?
    Totally addicted to boost.

 

 

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