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Thread: Rear Diffuser Build

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  1. #1
    Senior Member Azmodon's Avatar
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    Rear Diffuser Build

    I've been saying for a long time that I'd make posts about the stuff I'm doing... maybe it's time I actually do that lol

    Today's post: Functional rear diffuser build.

    Parts used at this point:
    2'x4', 1/8 ABS sheet ($20)
    2'x4', 1/4 ABS sheet ($27)
    16"x36", 3/4 Laminated Pine Shelf X 2 ($28)
    1.25"x1.25" Angle Iron - Two 5" lengths (one side has a 1 inch section removed creating a tab, which is bent up to match the required angle (7 deg.) ($scrap)
    Triple corner bracket X 2 (sandwiched by angle iron between front and rear assemblies) ($4)
    3" x 7" Mending Plate X 2 ($6)
    #6x32 Machine Screw X 8 ($2?)
    #6 Washer X 8 ($1?)
    #6-32 Nylock Nut X 8 ($1.50)
    1/4-20 Bolt @ 0.75" X 24 (Box of like 50 for $14)
    1/4-20 Bolt @ 1.25" x 12 ($3?)
    1/4-20 Bolt @ 1.50" x 4 ($2?)
    1/4 Washer X 54 (Box of 100 for $12)
    1/4-20 Nut X sum of ^^that (Box for $8)
    1.5" double wide corner bracket X 4 (for strakes) ($6)
    1.5"x2.5" corner brace X 4 (for wings) ($5)

    Parts being installed next:
    1" wide steel strip - from wing tip back to main body, bent at 90 and up to the ABS, fastened with one 1/4-20 bolt near the wings insertion point. ($9)
    1/4-20 RivNut near the end of the wing ($scrap)
    2" long 1/4" eye bolt mounted to the RivNut ($3)
    3" long 1/4" eye bolt mounted above the 1/4-20 bolt back at the main body through the upper end of the bent steel strip ($3)
    3/16" 7x19 coated aircraft cable attached through thimbles and cable clamps -> the 3" long eye bolt can then be tightened to pre-load the wing. ($6)

    (total cost... very very roughly = ~$160)

    The design:
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    The design... again:
    www.youtube.com/watch?v=EDy-UcvuLCM



    The ABS sheets
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    The Pine which was cut using printed templates
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    the two sections and wings laid in place + front and rear assemblies separately
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    Assembled
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    Underside view
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    Once the cutting out of the parts was complete I shaped the two short sections for the front using a sander (sloped the entrance inwards) -> the mid wing (large black thing - shown in red on the design) was hand planed in to an aerofoil using another template and its angle of attack set to 4.5 degrees.

    The rear pine pieces each diverge from mid-line at 7 degrees - the insertion angle of the rear and front assemblies is tangential, with the ABS sheet on the rear on a smooth curve (25' diameter) - mid point of the curve is 6.5 degree's from horizontal, ending angle is 11 degrees from horizontal. The idea being that, the mid-wing will assist in energising the boundry layer, helping air ride the upper surface - the 6-32 screws are also all offset from each other in this area and left at 0.5" in to the air stream so that their tiny bodies may provide a uniformly spaced set of vorticies.

    Questions / comments / etc. are welcomed - I also have a tonne of pictures regarding the removal of the interior components and carpet to put down dynamat, and I've got flares going on soon... and I'm having custom side skirts, somewhat similar to PCI Racings but "better" being priced right now.
    Last edited by Azmodon; 09-14-2017 at 04:00 PM. Reason: Added video

        __________________________________________

        click to view fuel log View my fuel log 2015 Micra SV automatic: 7.1 L/100 km ... 39.9 mpg (Imp) ... 14.1 km/L ... 33.3 mpg (US) ...


  2. The Following 5 Users Say Thank You to Azmodon For This Useful Post:

    Bobaganousch (09-19-2017),Daox (09-15-2017),IMPUL (09-14-2017),MetroMPG (09-20-2017),not_a_bot (11-02-2017)

  3. #2
    I like you. ����
    Can't wait to see it on the car. Looks great so far. Any plans to make more?

        __________________________________________

        click to view fuel log View my fuel log 2015 Micra S manual: 7.7 L/100 km ... 36.8 mpg (Imp) ... 13.0 km/L ... 30.6 mpg (US) ...


  4. #3
    Senior Member Azmodon's Avatar
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    A friend of mine has an audi A4 and wants a decorative one from 1 piece of ABS (or 2... specifically no wood) to mimic a rocket bunny, so come october I'll be taking measurements and stuff. I think if I do this again I'll remove the wood from the equation - having never worked with thick ABS before I didn't realise just how strong and resistant it is. The aerofoil could've just been a curved groove to bend a panel in to shape and mounting points on the side could all have been 1/4 - I'd just reinforce some points with extra wide washers. The cost would likely come out to that same.

    Being a first run though, and retaining wood templates if I wanted to build it again, time wise I'm sitting at ~3H cutting ~4H sanding and planing 2 nights wasted to painting - (reason alone to replace the wood with ABS, and I still have to give the wood a final coat of penetrol and a a thick coat of plastidip just to seal all the tiny gaps), ~5H bending / assembly... and like 7H of shopping for parts lol side note - only the really beefy metal brackets from homedepot will accept 1/4-20 bolts... found that out the hard way and drilling out holes can take a while with so many of them.

    To do it again but solid ABS... it'd likely drop from the ~19 hour first run, to about 6 if I preemptively had all the mounting hardware and bolts figured out

        __________________________________________

        click to view fuel log View my fuel log 2015 Micra SV automatic: 7.1 L/100 km ... 39.9 mpg (Imp) ... 14.1 km/L ... 33.3 mpg (US) ...


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    MetroMPG (09-20-2017)

  6. #4
    Quote Originally Posted by Azmodon View Post
    A friend of mine has an audi A4 and wants a decorative one from 1 piece of ABS (or 2... specifically no wood) to mimic a rocket bunny, so come october I'll be taking measurements and stuff. I think if I do this again I'll remove the wood from the equation - having never worked with thick ABS before I didn't realise just how strong and resistant it is. The aerofoil could've just been a curved groove to bend a panel in to shape and mounting points on the side could all have been 1/4 - I'd just reinforce some points with extra wide washers. The cost would likely come out to that same.

    Being a first run though, and retaining wood templates if I wanted to build it again, time wise I'm sitting at ~3H cutting ~4H sanding and planing 2 nights wasted to painting - (reason alone to replace the wood with ABS, and I still have to give the wood a final coat of penetrol and a a thick coat of plastidip just to seal all the tiny gaps), ~5H bending / assembly... and like 7H of shopping for parts lol side note - only the really beefy metal brackets from homedepot will accept 1/4-20 bolts... found that out the hard way and drilling out holes can take a while with so many of them.

    To do it again but solid ABS... it'd likely drop from the ~19 hour first run, to about 6 if I preemptively had all the mounting hardware and bolts figured out
    Sweet bro
    Attached Images Attached Images  

        __________________________________________

        click to view fuel log View my fuel log 2015 Micra S manual: 7.7 L/100 km ... 36.8 mpg (Imp) ... 13.0 km/L ... 30.6 mpg (US) ...


  7. #5
    Senior Member Azmodon's Avatar
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    :P once I get the mounting figured out, we'll see. It will likely require drilling holes in to where the jack is located / modifying the foam block to accept the rods - I'm thinking I'll square off the end of threaded rods and use long couplers, that way 2 wrenches can be used to adjust the height and angle at the rear - the front end will basically be touching the rear axles triangle box... thing.

    or... reinforced stainless corner brackets attached to the rear plate behind the bumper. Use 2 more chunks of angle iron, bolt them on at an angle, bracket to that so the rods are slightly tipped, preload it laterally so it can't swing... I'll have to draw this up to figure out the angles/length of rod/mounting locations... I'll be back some time next week with stuff

        __________________________________________

        click to view fuel log View my fuel log 2015 Micra SV automatic: 7.1 L/100 km ... 39.9 mpg (Imp) ... 14.1 km/L ... 33.3 mpg (US) ...


  8. #6
    Administrator MetroMPG's Avatar
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    Very cool! Subscribed.

    I love it when people make stuff for their cars.

    Looking forward to seeing this installed.

        __________________________________________

        click to view fuel log View my fuel log 2015 Micra S manual: 5.0 L/100 km ... 56.5 mpg (Imp) ... 20.0 km/L ... 47.0 mpg (US) ...


  9. #7
    Senior Member Azmodon's Avatar
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    I'm trying my damnedest to have it on for for the weekend... but the car's had to go back in to the exhaust shop this morning as it was melting my gas tank -> the flares should be mounted this evening as they're priority 1, but if everything looks fixed and there's daylight left I hope to get it on...

    Mounting is going to be "fun" - the only option is supporting the rear section through the floor - there's a control box and the muffler on the other side are blocking any chance of using exterior accessible positions -> 7/16ths rod and some nylocks will do the trick...

    The front though, the triangular tunnel that is the rear "axle" I guess, the nose of this thing extends just past it, and will basically be touching it at full extension (while jacked up)... should give me ~3 inches of ground clearance, which doesn't sound like a lot but I only have about 1.5 inches of travel before the body makes contact with the rubber of my tires... so it should be good but "mounting it" may involve metal strapping wrapped around the metal rods that hold the spare tire in place. Hence it "may not" be on before Quebec lol

        __________________________________________

        click to view fuel log View my fuel log 2015 Micra SV automatic: 7.1 L/100 km ... 39.9 mpg (Imp) ... 14.1 km/L ... 33.3 mpg (US) ...


  10. #8
    Senior Member Azmodon's Avatar
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    mini update - wing braces complete, steel on steel riv-nuts, cable's a little thicker than is stylish but at the extremely acute suspension angle, a 160lbs downward force can create a tension in excess of 4K... and I've figured out how I'm going to mount it finally so, aluminum tape to fill the gaps and a coat of plasti-dip to unify / last line of defence against water... and a pair of holes in the trunk... and she's ready to go on.

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    Currently I'm redesigning the redesigned splitter, because Infinity Wings are a thing and I'm not a huge fan of canards. The fun part now is getting the splitters inboard tire wake controls to feed the diffuser, while the outboard infinity wings interact with the skirts... yay CFD

        __________________________________________

        click to view fuel log View my fuel log 2015 Micra SV automatic: 7.1 L/100 km ... 39.9 mpg (Imp) ... 14.1 km/L ... 33.3 mpg (US) ...


  11. The Following 2 Users Say Thank You to Azmodon For This Useful Post:

    IMPUL (10-23-2017),not_a_bot (11-02-2017)

  12. #9
    So much want.

        __________________________________________

        click to view fuel log View my fuel log 2015 Micra S manual: 7.7 L/100 km ... 36.8 mpg (Imp) ... 13.0 km/L ... 30.6 mpg (US) ...


  13. #10
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    can we get some pictures of it mounted up!! looks great!

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