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Old 05-05-2010, 11:43 AM   #1 (permalink)
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Cheap carbon fiber hoods are almost as heavy as stock

Any time I remove components from the Insight, I weigh them. The stock hood, which is aluminium, weighs 9kg/20lbs. Being curious about the potential for weight savings with a composite hood, I looked up how much a riceboy carbon fiber hood weighs. Your run of the mill $600 CF hood for a Civic weighs 18lbs. So you probably save 6lbs versus aluminium. That's pretty unimpressive for $600. I'm sure the savings are even less for replacing plastic panels with carbon fiber.

However, I might be able to make my own carbon fiber hood for around $100 in materials. A hood-sized sheet of fiberglass cloth weighs 1lb per layer, and CF is lighter. Of course you'd have to add resin, and bolt on "features" like hinges, latch, and washer nozzles, but I couldn't picture it coming in over 7lbs.

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Old 05-05-2010, 11:53 AM   #2 (permalink)
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The lightest carbon fiber hoods are dry carbon, where they use vacuum bagging to suck out the excess resin, and tend to weigh in the neighborhood of 7-10lbs. If you could do that it would be impressive weight loss!
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Old 05-05-2010, 01:51 PM   #3 (permalink)
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Any quality fiberglass part will be vacuum bagged when its created.
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Old 05-07-2010, 04:23 PM   #4 (permalink)
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to give an idea of common steel in contrast, I just got shipped a 16.9 pound sheet of 18 guage with 4ft by 25 inch dimensions. I can only assume the hood is attractive to be lightweight.

I tend to go the other direction...the car even has strut braces by factory. Taking steel away is bad news. I can get away with aluminum in some places...

I'd like to know how this stuff works, I do not know many that go the expensive route.
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Old 05-07-2010, 05:24 PM   #5 (permalink)
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Quote:
Originally Posted by RobertSmalls View Post
Your run of the mill $600 CF hood for a Civic weighs 18lbs. So you probably save 6lbs versus aluminium. That's pretty unimpressive for $600.
6 lbs versus aluminium, but what versus steel? Never actually weighed a hood, but the Insight's aluminium hood feels like less than half the weight of a similar-sized steel one.
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Old 05-07-2010, 08:33 PM   #6 (permalink)
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The cheap carbon fiber hoods are not normally 100% carbon fiber, some of them don't even have any carbon fiber but dyed fiber glass or dyed pollyester cloth.
Other cheap carbon fiber hoods have a plastic, metal or fiber glass core, very few of them have stress points that crack or fold if you do get in a head on collision, I like metal hoods because they are designed to fold instead of cutting my head off.
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Old 05-27-2010, 10:30 PM   #7 (permalink)
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What Ryland said is true. Almost without a doubt the hood has the look of carbon fiber only. They either fake it with dyed fiberglass weave or they lay one lamina of carbon fiber fabric for the look and back it up with layers of glass fiber reinforced polymer.

S-Glass (a good glass fiber) has a density of 2.49g/cm^3, and a modulus of 86GPa where T300 (a lower end carbon fiber) has a density of 1.76g/cm^3 and and modulus of 230GPa. Just by switching to carbon fibers the hood gains several times the strength to weight ratio (Tensile properties are technically worse, but a hood is unlikely to fail in tension, it just needs to hold up to the wind under bending). Then there's the resin, which is a great percentage of the weight in a cheap layup and a small percentage of the weight in a high tech, vacuum bagged, oven cured, prepreg setup.

Note the need to have a vacuum in your oven and also notice only formula one, bikes, tennis rackets, and the newest airplanes are switching to carbon fiber instead of aluminum?

To point out one more thing, a crumple point for safety in a collision has to be designed whether or not the hood is steel or fiber reinforced polymer. If you buy a crappy aftermarket aluminum or steel hood you're probably just as bad off as buying the fiberglass one, in my opinion.
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Old 05-30-2010, 10:42 PM   #8 (permalink)
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To back you up, "every" (all 4 that I've had my hands on) MKIV Supra Carbon fiber hod that I have weighed comes in 3~5 lbs heavier than stock.
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Old 08-17-2013, 04:35 PM   #9 (permalink)
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You mentioned that when you took it off it weighed 9 kg/20 lb. Was that for the hood alone without the hinges or latch?
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Old 08-17-2013, 09:20 PM   #10 (permalink)
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Quote:
Originally Posted by Ryland View Post
Other cheap carbon fiber hoods have a plastic, metal or fiber glass core, very few of them have stress points that crack or fold if you do get in a head on collision, I like metal hoods because they are designed to fold instead of cutting my head off.
That's a point that many, including me, have always neglected.

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