I have never really understood the appeal of chrome. It really only points out that the part hiding underneath is low tech, over weight and its only trump card is that the part is shiny. You could argue that it prevents corrosion on ferrous parts but there are a lot of better options.
One of those high performance options is cadmium plating which has all sorts of great additional properties such as prevention of galling and a neutral galvanic coupling when used with dissimilar materials. I guess that is why Porsche used it so much in the past and why it is still the coating of choice for aviation. Unfortunately is becoming more difficult and expensive to use.
One of my other favourite coatings is ceramic. As seen in the photos, it has a lot of bling to it but has the performance to match. It isn’t only for exhausts systems, I use it for other external parts like aluminium manifolds and internally on piston crowns, combustion chambers and valves to encourage more heat out the exhaust.
The photo of the valves above show one pair that is coated next to the uncoated spares. The beautiful swirl polish finish of the custom valves is gone but heat reduction into the valve is measurable. The intake valve is cooled by the intake charge so it is normal just to coat the combustion side. The exhaust valve has a harder time so coating both sides can be an advantage and take some heat away from the guides. The same goes for the pistons like the GT2 pistons pictured above except a dry film lubrication is applied to the skirts. The coatings on the pistons are such an advantage that I don’t build engines with out the coatings these days…
I just had to include a few photos of the Lycoming 540 cold air induction manifold I just made and had coated. The thing is a monster! It looks like a giant spider – well, a spider that only has six legs anyway… It has injector bosses for calibrated injectors to be fired by a Motec M1, as opposed to the ridiculously basic aviation injection that makes K-Jetronic look like something out of Star Trek; tapered tubes, bellmouths in the plenum and all of those little details that take ages to fabricate and aren’t really seen! The Lycoming cylinders are not crossflow so the exhaust is in very close proximity and the entire exhaust and intake manifolds are therefore coated. (The picture of the merge collectors above are for the same engine).