Cool Coatings

As is typical with painted headers, the finish on the Blackjack painted headers (PN 85110) lasted about five minutes before it flaked off.

Jet-Hot says its double-coating process protects mild steel over 140 times longer than high-temp paint, more than 14 times longer than chrome, and more than five times longer than first-generation coatings. The coated Cyclones (PN 86110) survived the test with “no runs, no drips, no errors.”

Simulating a good high-perf street exhaust system, the headers dumped into 3-inch duals and DynoMax PN 17221 mufflers with 3-inch inlets and outlets.

We checked surface temperatures with a Raytek handheld digital pyrometer. This is the reading from the painted surface.

We found that the Jet-Hot coating cut surface temperatures over 50 percent.

Anyone who still runs painted headers is a flake! Factory-applied header paints have about a five-minute post-installation life span. From a longevity standpoint, paint just can’t stack up against high-tech ceramic coatings. But ceramics don’t come cheap, selling for up to twice the price of a set of painted headers. For some, the added surcharge might be hard to justify if it was just a question of looks alone.

However, ceramic coatings’ appeal is more than just the pretty wrapper. One of the leading exhaust coating outfits is Jet-Hot Header Coatings. Jet-Hot Sterling, its standard product, is a third-generation, aerospace-derived metallic-ceramic coating compound consisting of a proprietary, baked-on mixture of aluminum, ceramic, and sterling silver powder. The unique combo provides both high luster and good flexibility—if hit by a hammer, this ceramic won’t shatter like your toilet-bowl would. There’d be a dent, for sure, but the surface won’t break—an obvious advantage from both in-car installation scrapes and anti-corrosion standpoints.

Jet-Hot points out that realizing the full anti-corrosion benefits of header coatings requires coating the headers on their inside as well as outside surfaces. Not all competitors coat the inside surfaces, which isn’t good because exhaust gases themselves contain corrosive compounds. If the inside isn’t coated, the header eventually rusts through from the inside out. Coating only the outside can also cause another problem: Mild steel tubing fatigues when it gets too hot. An outer-only thermal barrier blocks the heat from radiating through the exterior metal surface, while the lack of an inner barrier exposes the metal to added “trapped” heat. In a scenario reminiscent of that caused by the dreaded “curse of the mummified headers” (outer cloth wraps used by some racers), the result can be literal disintegration of the mild-steel tubing.

The aluminum portion of Jet-Hot Sterling’s compound starts to melt at temperatures over 1,300 degrees F, but that’s OK for 90 percent of the applications out there. Cars running heavy loads of nitrous, a supercharger, or a turbo may need to move up to Jet-Hot 2000, which protects metals up to their melting point or 2,400 degrees F (whichever occurs first). The drawback is that Jet-Hot 2000 only comes in dark colors so it’s not as pretty. But the good news is that Jet-Hot 2000 usually eliminates the need for pricey (and hard to weld and fabricate) stainless steel tubing often specified in high-zoot nitrous or turbo applications.

The ceramic coating’s ability to trap heat aids a marginal engine coolant system in a closely cowled musclecar by reducing underhood temperatures. And as installed in a real car, lowering the ambient temperatures could also allow a cooler, denser fuel/air charge to reach the combustion chambers, offering more power-making potential.

By retaining heat within headers, the coating is also said to increase exhaust-gas velocity because hot gasses expand and travel faster. By smoothing the internal header bore surfaces, turbulence is reduced. The net result is more effective cylinder scavenging, which yet again offers a potential power increase. We recently had the opportunity to evaluate the effectiveness of Jet-Hot Sterling-coated headers on the Westech engine dyno. Like most header companies, DynoMax offers both painted and coated headers. It uses Jet-Hot as its coating supplier. DynoMax’s painted headers are sold under its Blackjack trademark, while the coated versions are marketed as Cyclones—but other than trade name and finish, the header designs for the same application are identical.

In our test case, the application was a GM 454 H.O. Gen VI big-block crate motor, officially rated at 425 hp and run as-delivered with a 750-cfm Mighty Demon carburetor. Tested on Westech’s SuperFlow dyno, the engine made about the same power and torque with both painted and Jet-Hot–coated header sets (see table). The numbers varied by less than 1 percent, within the dyno’s margin of error. Thanks to a wide-open dyno cell and hurricane-like air circulation fans, heat wasn’t trapped as it would be in a real car’s engine-bay. Engine coolant temperatures stayed under 155 degrees F, well below those encountered in a typical street car on a hot summer day. The absence of real-world “hot-soak” conditions probably accounts for the similar power and torque outputs in this case.

Header surface temperatures were a whole ’nother story, however. We checked header-tube surface temperatures both at idle and—in an attempt to simulate part-throttle, sustained cruise conditions—at 3,200 rpm with a light, 60 lb-ft load applied to the dyno’s water-brake. In both cases, the coated headers cut the painted set’s surface temperatures by over 50 percent. In a real car, this would significantly reduce both coolant and underhood temperatures. In the dyno-cell, we could actually touch the coated headers with our bare hands within 5-7 minutes after engine shut-down!

Headers aren’t the only parts that benefit from Jet-Hot coating; it can also be used on exhaust pipes, mufflers, and even (for emissions-reducing quicker light-off times) the catalytic converter. By applying Jet-Hot only to the top and bottom intake manifold surfaces, as well as the outer surfaces of turbocharger ducting, centrifugal supercharger ducting, and fuel-injection system air-intake tracts, you can keep incoming air and fuel cooler by insulating the charge from radiant engine-compartment heat. Yet headers remain the most common everyday application, and this test indicates that for the temperature reductions alone, this strong, durable, and “cool” coating is well worth the extra bucks.