Making a carbon fiber rear diffuser

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#1

Hello all, new to the forums here and I hope you guys can help me out.

This part, rear diffuser, is attached to the bottom of the rear bumper of a car. It will be very close to the rear exhaust tips. This part is mostly just for cosmetics and will not be very thick, about 1/8" thick.

So the requirements for this part would be:
1)Clear, so the carbon fiber and weave pattern will show through
2)UV Resistant, so that the part will not yellow
3)Low viscosity, because I want to vacuum infuse it
4)Able to withstand up to 250-300F, heat from the exhaust tips

Also, what gel-coat and resin would be suitable for this application? Again, it must be clear and able to withstand the heat from the exhaust tips.

I have been told by sales people that most polyester and vinyl ester based resins and gel coats may not hold up at those temperatures. So maybe I need to look for an epoxy based system?

Thanks all.

#2

Have you measured your exhaust tip temps? Those seem a little high as your exhaust cools quite a bit as it travels to the rear of your car. At idle I have pre turbo EGTs in the 900F range and I can easily hang on to the muffler tip. Every drag race my EGTs are well above 1600F (pegged gauge) and my plastic bumper doesn’t even show signs of heat never mind any kind of melting, not that I know what temp it melts at :slight_smile: You can see in the picture below that it sits quite close. My guess is the temps would be more in the 150-200 range which would open up allot more resin choices. The VE I am using for my hood has a heat distortion temp of 220F and a glass transition temp of 250F.

http://www.derakane.com/downloadServlet?docPath=DPAPP1.asco.ashland.com%5CData%5Cascc%5Cecomdocsasc.nsf%5CD9A1F619696AB18585256FE9004A596F%5C%24FILE%5CMOMENTUM411-350.pdf

#3

I have been trying to get someone to measure the temperatures since I have no access to the car. The car has an 2008-2011 Corvette chassis, around 600hp. So I assumed 250-300F but I maybe wrong. If PER or VE resins were used their HDT are only around 125-175F, would that be ok? I have been talking to some epoxy manufacturers they said that if the part does not experience any load at the elevated temperatures, then it would be fine.

#4

Ya, it’s always hard to find someone willing to sit on your trunk lid while you do some WOT pulls. :smiley:

The VE I linked had a HDT of 220. US Composites has a VE resin that I think is in the same ball park. I’ve never infused but the viscosity looked low enough from what I’ve read. Try giving them a call to get some specs on their resin.