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Old 06-14-2012, 02:04 PM   #1 (permalink)
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Mk2 Golf Kamm back - foam it or coroplast?

I'm after some opinions really, as I'm not quite sure what to do next. I'm making a Kamm back for the car, a quick bodge job as I have a long road trip soon. I have got this far:





and my original plan was to make a 'mould' into which to squirt some squirty foam which I could then shape, but looking at it today, I could also make it from coroplast, as I have a couple of sheets knocking around the place.

Coroplast would be simple, as I could just use the cardboard as a template, but it's white so wouldn't look so great (on the other hand I can't see it from inside the car). I won't ever be able to get the shaping 'just so' however.

Squirty foam is messy and sticky, but simple to fix, as it would just stick to the boot frame (old and rusty, and will be used to mould up a new one out of GRP in the future, so messing it up isn't a problem). I can also, with a bit of sanding and filling, get a really nice shape. Lick of paint and it'll look great. I will have to relocate number plate/lights and leave an uncovered part of the rear window for visibility.

Any recommendations?

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Old 06-14-2012, 02:08 PM   #2 (permalink)
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I'd go with the coroplast. You can even paint it.

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Old 06-14-2012, 02:24 PM   #3 (permalink)
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Will it not peel off? I'd heard painting it can be tricky. I could always try a test piece I suppose..
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Old 06-14-2012, 03:42 PM   #4 (permalink)
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Wow, that cardboard Kammy looks great!

I'd go with coroplast in the short term. It's relatively easy to cut and bend, but won't allow compound shapes, or at least they will be very tricky. On the other hand, you probably won't need compound shapes if the Kammback isn't too long.

Coroplast is what I made mine out of (see my mod thread) and it works great. The only thing I'd change is to make the bend rounder, ie larger radius, but that's a detail which probably doesn't make too much of a difference. Also, everyone warned me that paint won't stick to the polypropylene, but it's only flaking in a few small places after three years of parking outside year-round.

If this is a short-term project, then go with the coroplast. After a few months you'll see what to change in the final version (for which I recommend glass-fiber) when you finally go about making it.

Oh, and two suggestions:
  • I've read that closing the rear wall of the Kammback is better. I think someone here even tested it? If you use a piece of clear plastic to allow rear visability, then you can fold you passenger side mirror.
  • Get rid of the front mud flaps!!!!
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Old 06-14-2012, 06:44 PM   #5 (permalink)
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My OPINION would be to go with option 3 and heat form some lexan and make a flat closure on the back side, paint-match the upper part and leave the rear clear.

If you do use spray foam, let it sit about a week before covering it with anything( even paint) as this will give it time to FULLY cure and won't bubble/warp like my tail is doing right now because I rushed to get it semi finished before the SMCC Rally this last weekend. After a week you can use fiberglass resin to make it tough as nails, and then sand to shape as you see fit.

Coroplast is fun to work with and can be made to do some funky things as some of the artists around here have accomplished with a little creative engineering. Closing the end with lexan will give you the full benefit of view and solid rear face.

Hope that muddies the waters even further and I can't wait to see what you come up with.
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Old 06-15-2012, 03:12 AM   #6 (permalink)
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Thanks guys. I think I'm going to go with the coroplast option, as I now have a decent template to work from. Squirty foam will be too messy I think, but would be a good base for GRP. I think once I have evaluated the benefits of such a mod, I'll be in a better position to decide if it's worth the outlay for resin, cloth, and all the other sundries, and then I may be into trying to get a really good shape with foam.

I must find some lexan/polycarbonate, as this Kamm back does seem loads more sturdy with a back piece fitted.

Off outside to remove the mud flaps as we speak! Thanks again for the input folks.
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Old 06-25-2012, 04:33 PM   #7 (permalink)
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Right, this is my third attempt, and I still don't think it's quite right. It is however, glued on good and solid, so it's here to stay. I've overlayed the aero template using seifrob's online tool, and my kamm back does seem to go down at a little too steep an angle. What do you think?



I put the template that far back on the roof because it's pretty much flat all along it. I haven't had the chance to test it properly on a known route, but it 'feels' -ahem- better. Will it give any benefits at all being this far below the template line?

Also didn't get round to removing the mud flaps.
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Old 06-25-2012, 08:25 PM   #8 (permalink)
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While it's steeper than the template, it's still OK.
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Old 06-26-2012, 05:09 AM   #9 (permalink)
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The flatter angle would give you slightly better rear visability. The Kamm you have now reduces rear wake, but maybe at the cost of more lift. It probably breaks even, so it's not a big deal.

You can also try to extend back another few centimeters to the end of the bumper.

If you had the time and place you could test 2 different angles, depending on where you place the template.
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Old 06-26-2012, 01:33 PM   #10 (permalink)
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Phew, so it's not a total bust then. As it happens, I was hoping to extend it a lot further, but after some trimming and folding this was what I ended up with. It is at least quite solid. Today I sprayed it with a little stonechip paint to (try to) match the textured plastic on the rest of the car:



Rear visibility is still ok, just about. The issue of lift hadn't really occurred to me. It did feel a little more tail-happy into corners when driving at speed - I had assumed that was the weight of all the beer I had loaded in the boot for midsummer.


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