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Thread: Carbon diffuser? You can make too! Here's how with pics.

  1. #1
    Senior Member Chairs with flares's Avatar
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    Thumbs up Carbon diffuser? You can make too! Here's how with pics.


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    The plan was to make a carbon/fiberglass rear diffuser for downforce as an adjustable wing would look too funky on a small hatch.

    Here's how it all started;


    The first thing to do was to determine the size and curve of the main diffuser panel. The optimum trailing-edge angle was determined to be 10*-15* up from horizontal over a fairly gradual radius. The diffuser creates downforce by helping the higher pressure air flowing under the car transition into the low pressure area directly behind the car. As a result, the vacuum behind the car essentially 'sucks' the air out from under the car, creating downforce. Any steeper angle on the trailing edge and the air won't follow the diffuser and it won't be as effective (unless it's really close vertically to a wing; e.g. Formula Ford cars)

    Using cardboard, we made a rough template of the curve and size available within the dimensions of the car's floorpan and rear bumper cover.




    Using this template, a mold was made up to allow the carbon and fiberglass to be laid to the right shape. I just made more of the above template and used them as 'ribbing' to bolt together a wooden frame topped with MDF board then aluminum sheeting from Bunnings. Aluminum is chosen for it's ability to de-mould itself from carbon cleanly.



    I also made a smaller form purely out of cardboard to mark the cut-outs needed in the main panel to allow clearance for the exhaust muffler and factory tow-point.



    Time for the fun and stinky stuff! I'm gonna skip the stuff on laying down fiberglass as that's fairly simple and there are many tutorials through google. For carbon, make sure the weave is even at right-angles, as any imperfections will show up. Also, make sure you have enough material to cover your mould with a little hanging off the side and really wax the mould with mould release agent (4+ coats).

    First layer of carbon/resin.



    Then 2 layers of rough fiberglass matting, a sheet of 3mm MDF board, and another layer of fiberglass to seal it all up. The MDF board gives a stronger base to mount through, reducing the risk of any mounting bolts pulling through the diffuser.



    After leaving it 48hrs to cure, pop it out of the mould by going aroudn it with a spatula. Here is when you find out whether you used enough release agent.

    Use you cut-out template to mark and cut the main panel to shape and make sure it all fits around everything.

    I then glued a strip of rubber 'U-section' with silicon around all the edges to hide imperfections and well as sticking a single layer of dry carbon on the top where it sticks out past the rear bumper cover.



    Now is when you decide how you mount it on the car. Being a FWD hatch, I had the luxury of simly bolting it to the floorpan in the spare wheel well. If everything went well, this will be where the MDF in the diffuser sits. The rear of the diffuser was decided to be bolted to the bottom of the rear bumper cover. Once the mnounting holes were mocked up, design for the strakes/fins can be done.

    The strakes stop the diffuser drawing air from the sides, only allowing it to draw air from under the car. Ultimately, they should taper out towards the rear slightly. I used scrap dry-carbon to use as I had some lying around, mounted with 'L brackets' for shelving
    through some of the holes used for mounting to the car body.



    All mounting hardware was stainless steel, using 6mm allen-key bolts with Nylock nuts to prevent vibration induced loosening.

    Finished product;







    And everyone's happy!




    BIIG cheers to Busby (User ID: Mike86) for the inspiration and help through this shoddy weekend backyard project. He's the man to see for carbon blanking panels (radio delete/ac vents/speaker holes/etc).


    Oh, and it seems to help with high speed stability on the track. Combined with front canard spoilers, cornering at previous speed felt much more stable and less 'floaty' allowing faster cornering. In short, it was a success!

    Last edited by Chairs with flares; 27th February 2009 at 08:34 PM.
    J.

  • #2
    carbonae86
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    Nice when are you making ones for toyotas

    Or maybe that should be for toyota that arent cut up since thats the rage now

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    Veteran biggo's Avatar
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    Hahaha thats cool. I noticed they now make carbon weave look fibreglass now too. Might have a go at something like this oneday.
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    Senior Member mack 10's Avatar
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    i enjoy resin


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    thats awsome

    mike i never new your skill well done

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    hahahahaha..........hahahahahaha

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    Senior Member squish_m8's Avatar
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    that's great

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    Senior Member KKUSTOM's Avatar
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    saw this today awsome job dude. helped him grip like a beast. lol

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    when r u putting this into mass production 4 us all

  • #10
    Just here for the scene... ArbPotatoes's Avatar
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    Make diffusers for 86s and KEs and sell them haha

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