RS6 undertray

[IchBautAuto]

The dreaded undertray, mine is toast. Gregstv has lent me a spare while I try and replace it. The German source may be out due to Covid but they reply with a form email and then dead silence over the last month. Locally they are the equivalent of 700 pounds which is starting to border on the rediculous. So, I have decided to make a GRP version. This is not my trade but I'm confident I can produce something that is true to form and acceptable to bolt under the car. It's a cheap trial and nothing lost, nothing gained. Back in 2019 they (other UK audi forum) produced an RS4 undertray in the UK which was very successful so it's no pipe dream.

Just had my RS4 windows tinted and have a few other things to address and then I'll start. Will post up progress when there is something to see and if it is successful then some enterprising chap may take it up as a solution when all the other options are exhausted.

[Mark-RS]

This should be rather interesting. I believe not so long ago there was a post where someone had either made one, or modded another to fit and the results were pretty good.

Not sure where the post was, it was a while ago I saw it, maybe even before I bought my car and was snooping for info before purchase.

[steve2003rs6]

Try Steve green 07835 176599 in the UK.
God knows what shipping costs would be to Australia.

[Siph3r]

Will i even make the undertray from an A6 fit in any way? Have a donor parked out front...
I know there are major differences(width and lenght)

Just found out that the one one the RS6 is gone and I have no clue when that has happened


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[Shoppinit]

Maybe an A6 V8. But the vents will be in the wrong place.

[Mɐʇʇ]

I've done quite a bit of glassfibre, including building and restoring a few boats, so if I can help with advice or guidance, just let me know. And if I don't know, I know a man who will.

I find the shapes of these things a bit of a 'mare - I suspect a multi-part GRP thing with the NACA ducts bonded in seperately using sikaflex might be worth thinking about.
I know everyone will encourage all kinds of exotic fabrics, but in truth, 3 layers of 600g chopped strand will probably be about right and will be easy to chop, grind and fill to get a good fit.

[IchBautAuto]

Good news, initial plan is to use 2 layers of twill with a third layer in the weak points. Just plain polyester resin. I have access to kevlar etc but far too much trouble for me to even consider it. Pre preg CF was calling me and it would have been a doddle except I don't have access to an oven that big. One piece mould for the underside and a separate for the inner section of duct and probably just use resin to join them. Of all the things it actually looks quite easy.

I'd imagine that my initial questions are going to revolve around mould preparation and release agents. Done some reading and the six layers of wax seems painful. I've used CSM way back and Ive elected to go upmarket for this, lets see if it is a dumb choice.

[Mɐʇʇ]

have a look at sikaflex for joining seperate bits - it stays flexible, but sticks good and proper