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Carbon Fiber Rear Diffuser and Body Panels


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After seeing xcarguys's flat bottom and rear diffuser and hearing about the benefits of both I decided that I had to have them for my V6 Stalker Classic.

 

At the same time my son who is a High School Senior this year and going into engineering asked if he could buy Carbon Fiber and make some parts.  The timing was great so I cut him a deal and told him I would buy the materials if he made parts for my Stalker.

 

Not sure if the parts will turn out well but this thread will document the process and parts we are making either way

 

 

Edited by searya
typo
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So lets start out with my goals.  

 

  1. Create a flat bottom to the car (as much as possible) - this is necessary according to the internet in order to make the air flow smoothly to the diffuser.  Without this they say diffusers are pretty much for show
  2. Make a rear diffuser so that I increase downforce without much drag
  3. Make side body panels for the car
    • I might make the main nose panel in the future but not real interested in taking on making a mold right now
    • I want carbon fiber fenders/wings but if I can buy them vs. make I will
  4. Keep it as light or lighter than the aluminum option 
    • After taking a passenger on several laps during my last track day I got first hand experience with how weight slows you down.  I lost 4-6 seconds per lap with a 180lb passenger in the car
  5. Since carbon fiber is way more expensive than aluminum I hope it will look cool
    • right now my car is a very functional track car but lets put it this way I am not afraid to pull out an angle grinder to grind down the fenders or make something work with duck tape should an issue arise while at the track.
    • After making the carbon fiber parts hopefully it will look good enough for me to at least think about it before making a track side hack :)
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Posted (edited)

Parts List and Links to what I bought (fyi I was surprised to find out it takes a lot more than just the carbon fiber cloth):

  1. Carbon Fiber Cloth 
    • There are lots of different weaves a weights and thread counts but for this I bought Toray t700.  
    • Main reason is it supposed to be good and I found a deal on Facebook Marketplace where I got it for $16 a yard vs $42 retail.
    • Yards are 50 inches x 36 inches
  2. Foam Core - used to give rigidity and strength to your parts without increase weight
    • Buy the ones linked here as they are definitely the best value out there in the 4pack of 2x4 feet wide so shipping isn't crazy
    • I bought 2 4 packs of the .125 inch thickness
    • Note: I also bought 1 4 pack of the .375 thickness at the same time since it didn't cost more to ship and I may use it for the diffuser.
  3. Resin and Hardener and Pumps
    • I just told them I wanted glossy and clear finish and they recommended this one
    • I bought the linked kit which was 1 gallon resin + 1/2 gallon hardener and you mix it 2 to 1 so you run out at the same time
  4. Peel Ply - this is plastic that won't stick the Carbon Fiber Resin 
    • I bought 5 yards to start with
    • I bought the 60 inch wide yard
  5. Breather Cloth - this allows sucks up excess resin to reduce weight and also allows for even vacuum pressure
    • I bought 5 yards to start with
    • I bought the 60 inch wide yard
  6. Jumbo Vacuum Bag - like a big zip lock bag.
    • Kit from target came with 2 bags 48 inches long by 35 inches wide
      • I have been using a 5hp shopvac to suck the air out of these bags
      • Seems to work well and WAY less hassle than making your own bag
    • Note: for the diffuser I will have to make my own vacuum bag since the part is too big to fit in the one from target.  For bigger pieces like that you will need:
      • plastic - to make the bag. They sell special plastic for vacuum bags but it costs way more than the stuff from home depot so I am going to try that first
      • butyl tape - used to make an airtight seal between the plastic and the table your part is on.  Buy it from amazon vs the carbon fiber dealers as it is cheaper
      • vacuum pump - I bought this one on facebook marketplace for $125.  Really I think any vacuum pump would work.
      • vacuum bag connector - punches through the plastic and then runs to the vacuum pump to suck the air out.
  7. Release Wax - used to coat the surface that the carbon fiber rests on so it comes free once the resin cures
  8. Glass - used to give the carbon fiber a smooth surface and it is easy to clean the resin off of when you are done
    • Search Facebook Marketplace and buy a piece of glass, shower door, glass table or something vs. calling a glass shop
    • I bought piece of glass that used to be in storm door.  It was 32x70 inches and was $10 
  9. Plastic Spreaders - used to spread out resin so you don't have build up in one area
    • I bought 5 and you can clean them with alcohol after use if you don't wait too long
  10. Wedges - to separate the finished carbon fiber part from the glass base
    • I bought 3
  11. Cheap Paintbrushes
    • I just used ones around my house
    • I plan to try foam brushes next and will you know if that works better
  12. Fabric Scissors
    • Regular may work too but I my wife had this pair and it works great to cut the carbon fiber
Edited by searya
added some items to the list
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  • 2 weeks later...
Posted (edited)

Wanted to post my first update on progress.

 

My son and I have made two of the underbody pieces so far and just today made a good mockup of the rear diffuser including Rakes using this HardBoard from Home Depot (only $12 for a 4x8 sheet and real easy to cut with a jug saw).

 

First off how we made the first 2 underbody Panels (Panel 1 = right behind the nose cone and before the oil pan, Panel 2 = driveshaft cover)

 

1. Mock up the Piece you are making using Cardboard or the Hardboard linked above.   

  • I used cardboard but if I did it again I would use the Hardboard as it doesn't flex like the cardboard does and is just as easy to work with.

2. Wax the Glass you bought with 4-6 layers of the Release Wax.  

  • So far the release wax has worked great for us. The carbon fiber piece with resin cures right on the glass with the wax and when done curring it has popped right off the glass for us.

3. Using your Mocked up Piece, cut out all of your materials (details below):

  • Note 1: I recommend cutting the Carbon Fiber last as the less you move it the better off you are. 
  • Note 2: Also be gentle with the carbon fiber as the weaves can shift and and any place you grab it tightly will likely show as an imperfection in your final product.
  • Parts to Cut:
    • Foam Core - Cut 1 piece to the exact size of your mocked up part
    • Peel Ply - Cut 2 pieces to big enough to cover your part plus a few inches on each side
    • Breather Cloth - Cut 2 pieces to big enough to cover your part plus a few inches on each side
    • Breather Cloth - Cut a third piece of breather that you can run from the Part you are making to the vacuum attachment hole.
    • Carbon Fiber Cloth - Cut 2 Different Sized Pieces using your Fabric Scissors 
      • Cut 1 should be 4 inches bigger on all sides than your mocked up part (the extra allows you to wrap it to the backside)
      • Cut 2 should be cut to the exact size of your mocked up part

4. Making the First Side of your part:

  • Adhering the Carbon Fiber cloth to the Foam Core
    • Take your Foam Core and give one side of just a light spray of spray adhesive so it has a tacky feel (I used 3m super 77 from home depot).
    • Gently pick up your big piece of Carbon Fiber (cut 1 above) and lay it down on the tacky foam core
      • I try to hold it from underneath with my palms and pinch it a little as possible with my fingers
      • When laying it down on the Foam Core I try to let it droop in the middle and then move my pawns out slowly so it goes to the edges
    • Make sure everything lines ok and then apply even pressure directly downward to get the carbon to stick evenly to the Foam Core
    • Once stuck flip the Foam Core over and give a light spray to the edges of your part where the carbon fiber will wrap to.
    • Wrap the edges and once again make sure everything lines ok and then apply even pressure directly downward to get the carbon to stick evenly to the Foam Core
  • Mixing your Resin and Hardener
    • Note: with the Resin and Hardener I bought you want to get everything below done and vacuum bagged in about 30 minutes after mixing them
    • Each Weight of Carbon Fiber and Each type of Foam Core needs a different qty of the mixture
    • For the my Carbon Fiber Cloth and Foam Core  I needed 95grams combined per square foot (144sq inches)
      • My Resin to Hardener ratio is 2 to 1 so that gave me
        • Resin 63grams per square foot
        • Hardener 32grams per square foot
    • Figure out the square feet/inches of your part and use that to determine how much Resin and Hardener  you need to  Pump out and weigh the amounts to ensure you got what you need (I used a digital food scale that can be zeroed out for the weight of the cup and measure in grams)
      • I attached the calculator spreadsheet I use.  Just enter the square inches in the green cell and it will tell you what you need.
    • Mix the resin and hardener using whatever you want (i used wood popsicle sticks and mixed them in a plastic disposable cup)
  • Applying the Resin
    • Using your throw away paint brushes apply some resin to the waxed area of your glass
    • Apply resin to the part you are making until is it fully saturated
      • No real trick here just don't let bristle fall off and don't apply lots of pressure that could move the weave
      • If you have build of resin in area you can use your Plastic Spreaders to move it around the part and even it out
    • Flip the part over and place it on the resin area of the glass
    • Apply resin to the carbon fiber you wrapped to the back side of the part (just the carbon fiber portion no need to put resin on the still exposed foam core)
  • Vacuum Bagging the Part (this applies nice even pressure and removes any excess resin weight)
    • Put 1 piece of your Peel Ply on top of your Carbon Fiber Part
    • Put 1 piece of your Breather Cloth on top of your Carbon Fiber Part
    • Put your 3 cut of Breather cloth running from the breather on the part to the vacuum attachment hole
      • This allows the vacuum to suck the air out as the breather prevents the bottom of the bag from sealing the air extraction point
    • Put your cheap roll plastic on top of everything (don't let this cover the air extraction point
      • I do this so that if Resin seeps through the breather cloth it doesn't stick to the expensive vacuum bag
    • Get a helper and have one of you pick up the glass with the part on it while the other slips the Jumbo Vacuum Bag over the part
    • Seal vacuum bag (basically a big zip lock end)
    • Attached your vacuum or shop vac to the air extraction port
    • Flip on the vacuum and watch all the air get sucked out and the part become visilbe 
  • Removing the part and seeing your creation :)
    • Wait 12-24 hours for the part to cure
    • Release the vacuum from the bag
    • Remove the Glass with from the bag
    • Separate the part from the glass using your Wedges 
  • Clean up:
    • Spray the glass with rubbing alcohol and
    • Use a razor blade to clean off an expoxy resin on the glass
    • Repeat until clean and ready for next part.

 

5. Adding Carbon Fiber to the back side of your Part

  • Follow the same steps above but use the small piece of Carbon Fiber (cut 2 above)

 

 

 

Resin and Hardener Calculator.xlsx

Edited by searya
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Below are photos of the Parts and steps described above:

 

Applying the Carbon fiber to the Foam Core with adhesive

 

IMG_1589.thumb.JPG.0bebd1f7eb2555e8003d1ab6edbc677e.JPG

 

 

 

IMG_1636.thumb.JPG.4614b4907604bbc6c3452bff43f384b5.JPG

 

 

Saturating the Carbon Fiber

IMG_1593.thumb.JPG.4c1e3be40449bfffbb5e7ef7de760e83.JPG

IMG_1592.thumb.JPG.0114114da1f77de6f7c54cd8a1f03438.JPGIMG_1594.thumb.JPG.5820ee5aa0d4cc9182391cc08db659d8.JPG

 

 

IMG_1638.thumb.JPG.1eca625021a617e1cad65ffb82835360.JPG

 

 

Finished Parts!

 

They turned out really nice.  Very hard, and very light.  They also had nice shine to them.  Not perfect but not bad for the first couple of pieces considering no sanding or second layers of resin were applied.

 

IMG_1605.thumb.JPG.0a28afff89556110f771f1e4d1d144a7.JPGIMG_1606.thumb.JPG.1b9603fad09ac51d75ee12a773ba7db3.JPGIMG_1635.thumb.JPG.f24e0c2af67abadc79a309b224e1aa38.JPGIMG_1637.thumb.JPG.b015119163f04e9c590c407098769dcf.JPG

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