Exhaust manifolds on cars (and other engine powered vehicles) are usually make of cast iron and VERY heavy. Car tuners usually will replace them with a thinner walled tubular pipe style manifold to save weight and to get better flow and performance (at the expense of being louder, but that’s often considered one of the benefits as well).
Carbon fiber is used increasingly in motor vehicles to save weight and increase strength. It’s also becoming more possible to do custom moulds using carbon fiber, so that more comples shapes can be formed that just basic sheets or tubes. Why hasnt carbon been used for an exhaust manifold yet?
Temperature is the reason. Carbon usually uses a type of epoxy or thermoplastic as the binder for the layers of carbon. This works fine for normal operating temperatures, but when these are increased the epoxy is not able to handle the higher heats- it melts or burns away, leaving just the cloth again.
A recent lamborghini prototype (and maybe production car? need to find the link again) boasted that it had a full carbon fiber exhaust, which means they must have found and used a binder that can handle far higher heats than normal epoxy. After some digging, I found this company Polymeral (http://pyromeral.com/) appears to be the one making this high-temp carbon process a reality.
I’m sure it’s super expensive for now, but it will be nice to see what kind of lower cost exhaust options become avaialble later as this technology becomes proliferated. Not only will this make a much lighter exhaust, but the custom shapes that can be moulded will even allow more fully tuned header shapes, including smooth tapers and calculated optimizations.
Update- a video from the Pyromeral guys –