What Are Carbon Fiber Hoods?
Carbon fiber really is one of those miracle materials of the modern age. This stuff is so strong, light and versatile that manufacturers are daily trying to figure out ways to reduce production costs so they can start molding entire cars out of it. Lamborghini is already doing just that with its Sesto Elemento; apart from the engine block, gears and a few nuts and bolts, the Sesto is nothing but carbon weave. Carbon hoods have been a mainstay among performance enthusiasts for about a decade; just be sure to keep your expectations realistic before bolting one to your ride.
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Carbon Fiber Basics
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Formally known as "carbon fiber reinforced polymer," this wonder-material of the space age is essentially a polymer epoxy -- something like the resin used in working fiberglass -- impregnated into a weave of pure carbon fibers or a mixture of carbon and Kevlar, aluminum or glass. Carbon fiber is usually made using one of two processes; either dry carbon sheets are laid into a mold and injected with hot resin or epoxy, or the fiber weaves comes pre-impregnated with a polymer that turns into a liquid and binds together under heat and pressure. These manufacturing processes make carbon fiber expensive and difficult to repair, but they're also what give it its strength.
Weight
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Weight reduction is carbon fiber's reason for existence. Originally designed as a replacement or supplement for steel, aluminum and fiberglass in aircraft, finished carbon fiber has all the structural rigidity of steel at about one-fifth the weight. Using a carbon fiber hood, roof or trunk/hatch panel is a quick way to not only reduce weight but take that weight off of the highest points on the car. This lowers the car's center of gravity, which decreases body roll without resorting to stiffer springs and shocks. This is an important consideration for luxury sports car manufacturers like BMW's M division, which specializes in providing maximum handling performance with minimal driver discomfort.
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Appearance
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Even the most Luddite of traditionalists would have a hard time disputing carbon fiber's inherent intricacy and beauty as a material. While the carbon fibers themselves are black or gray, they're also slightly transparent and shimmer in the sun; think of a graphite pencil lead -- which is also carbon -- and you've got the right idea. Once it's impregnated with a thick coat of glossy resin, a curved carbon body panel the intricate weave takes on a certain depth and glow that's impossible to mistake for anything but carbon fiber. Granted, unpainted carbon fiber is considered something of a gauche faux pas in Asia and Europe.
Other Functions
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While most companies that produce carbon fiber hoods make replacements indistinguishable from stock when painted, many consumers opt for a little something extra while shelling out the money for carbon. Many carbon fiber hoods come with one or more backward-facing louvers that, apart from looking racy, work to keep high pressure air from building up under the hood. High pressure under the hood not only reduces airflow through the radiator and intercooler, it also lifts and destabilizes the front of the car at high speed. The downside to using louvers is that they'll let rain in to drip on the engine if you don't install a rain tray beneath them, and they'll immediately peg the driver as either very fast or very delusional.
Drawbacks
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Carbon fiber is far more expensive than steel; not just expensive to buy, but expensive to fix and a bit harder to maintain. Polymer resin isn't as hard as paint, which means that it may pit more easily when hit with road debris and will haze over if you don't regularly polish it. The epoxy doesn't particularly like UV radiation or direct sunlight either, which means that you'll need to keep a UV-resistant wax on it and try to park in the shade. While carbon fiber may be harder than the equivalent steel, it will crack instead of bend when its limits are exceeded. So that "my friend sat on the hood" dent that might otherwise pop out with a hard smack to the bottom of the sheet metal ends up turning into a very expensive trip to a very expensive body shop.
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References
- Race Car Engineering and Mechanics; Paul Van Valkenburgh
- Build Your Own Sports Car on a Budget; Chris Gibbs
- How to Build a Winning Drag Race Chassis and Suspension; Wayne Scruba
