While headers may offer more performance, nothing fits a specific car like the stock cast iron exhaust manifolds, and when the car is restored or original, they are necessary. The problem with cast iron, especially exhaust manifolds, is that it rusts. The constant hot-cold cycling creates a lot of moisture, which causes rust on the cast iron, wrecking havoc on their appearance. The typical restoration practice involves cleaning and painting.
Painting exhaust manifolds has its own set of problems. If the manifolds are not perfectly clean, the paint won’t stick and flakes off. Even if they are sandblasted and ultra-clean, high-temp paints eventually burn off, leaving a patchy, unnatural looking manifold.
There is hope however, as an industrial product has found its way into the automotive restoration world. It’s called Slip-Plate, which is a liquid graphite product that is typically used as a dry lubricant in many industrial and manufacturing processes. Slip-Plate uses a liquid solvent binder to which powdered graphite is added. We ordered the aerosol version (which is best for this application) online at www.slipplate.com, but it is available as a brush-on as well. When sprayed, the solvent binder adheres the graphite to the part. After about 20 minutes, the solvents evaporate and the graphite is left on the surface, permanently bonded. The good thing about the liquid binder is that it allows the graphite to flow into the pores of the cast iron, even better than paint, yielding a stronger bond to material. In addition to the better bond, the graphite is designed for extreme temperatures and pressure. This ensures the graphite won’t burn off after just a few trips down the road.
With the technical stuff out of the way, we can get to the point. Spraying the Slip-Plate is much like paint, too much and it will run. Spray the graphite in several thin layers, allowing each coat to dry (between 5 and 10 minutes) before applying another. After the spray dries (20-40 minutes, depending on the atmosphere and thickness of the paint) the top surface will have very dark, dull look. The trick to whole process is to buff the surface using a soft shop towel (don’t use the wife’s good towels, she will probably kill you) which brings the surface to a nice subtle shine. This nearly, perfectly matches new cast iron. It is wise to let the parts sit for 24 hours before running the engine. This ensures the solvents have fully cured and won’t cause any outgassing (release of gasses caused by heating, resulting in bubbles). As a side note, be sure to spray this stuff in a well-ventilated area, it is just like paint and really stinks up the shop.
With everything painted, buffed and the manifolds reinstalled, its time to get down the road. As with all things, there could come a time when the graphite needs a little touch up. Using a small chip brush or even q-tip, any faded areas can be touched up in the car. Spray a little Slip-Plate on the brush or q-tip, dab it on, buff, and you’re done, no need to pull the entire manifold. The graphite blends in very well and, unlike paint, will not show any evidence of a repair.