George R is no longer at Kooks..has not been for a while.
I always warn people that coating is something you have to really take people's opinions with a grain of salt. The main reason is coating is not a profit base...and adds some complexity to processing orders.
So for a company...what would you rather do? Sell someone a header and be done with it
.......or....
Sell them a header, with coating at no margin, then deal with shipping the headers to the coater and back, and the customer support of "When will my headers be ready". Then if the customer has a warranty issue with the header, they will likely expect you to recoat them for free also. Selling coated headers requires a lot more leg work.
As a manufacturer there is also a pride issue. Most people see coating as preventing rust...and when you are making a high end stainless header, saying it needs to be coated would be like saying there is a problem with the quality of the stainless.
I have discussions with Kooks, and I suspect this is why they push customers away from coating. It's easier to say it is not worth it than deal with it.....unless of course you are willling to pay $350 they charge to do it
Coating is not 100% necessary on a stainless header, but it is an added positive if you do decide to order them with it.
Is an uncoated stainless header going to be any hotter than cast iron manifolds?..likely not. However will coated stainless headers be quite a bit cooler than uncoated headers or cast iron manifolds? You bet ya!
Coating is not going to show up on the dyno, however it will show up hot lapping at the track. I have hot lapped the crap out a car with coated headers before and been able to come back 15-20 minutes later and the header was cool enough I could touch it with my bare hand. That means under the hood cools down quicker, and you get more repeatable results at the track. Also coating makes you engine slightly more efficient. Because the header traps exhaust heat inside the header, the exhaust gas becomes more pressurized, and leaves the header faster. The faster the exhaust leaves the head, the easier your engine breathes. The common excuse I have heard from tuners of the years as a reason not buy coating is that a coated header reduces how much you can advance the timing vs. an uncoated one. This is a half true, a coated header does require less timing advance, but does not make less power.. This is because you advance timing to help correct an inefficiency. The coated headers make the exhaust gas flow better, making the fuel burn quicker and more efficient, so less timing advance is needed to make the same power.
As for durability, coated headers are very durable. Failures are rare, and when they do happen, are almost always due to the car being run lean (normally during tuning process). You can tell this because the coating discolors around the flange where the primaries bolt on to the engine. The coating does its final curing the first time you run the car, and all the headers we send out have instructions from the coater that say to either drive the car for 20 minutes at highway speeds, or let the car idle for that long with fans running under the car. A common mistake I see is to install the headers, and roll the car on the dyno and start tuning. This is the worst thing to do because the car is not tuned right, and the dyno is the hottest your car will ever be.
As for coatings, I recommend to most of my customer to our polished silver coating options. These are very durable coatings that are cleanable, and will last as long as you have the car with proper maintenance. With coating, you have to understand first off the basic idea, which is to bake ceramic power on your header. It is, in the simplest terms, pottery baked on your header. The coating companies mix in different things to give it a desirable appearance. For instance, the colored coatings (black, blue, gray), all have different resins mixed in. These coatings work good, but in terms of appearance they are the least forgiving. If you over heat a colored header, you burn the resin, and it wil create a discolored spot where the resin was damaged. These coatings can also be stained by fluids. With the silver coatings I recommend above, they mix in silver and aluminum powder, and then after the header is baked, they polish it. This gives the header what I call a 7/8ths chrome appearance. It looks like chrome from a distance, but when you get close, it has orange peel to it. This coating looks good on anything, is wipe able, and best of all can be polished back to a shiny finish. When you over heat a silver header, it will normally only lose some luster, which can be restored by simply polishing the header.
I personally am ambivalent at this point. As stated, a coated header is a bit more work on the business side..so if you want uncoated, I am not going to push you. It's less work for me, and to your average customer is not going to notice a performance difference driving the car (kind of like most cold air intakes, haha). The flip side is, I offer coating, and personally recommend it because I do believe it works, and ensures you will get every bit of performance out of your expensive header purchase. Every GM LSX I have ever owned, has had coated headers on it because I have seen how fast the headers cool down..and simple common sense tells you that anytime you can cool down something mechanical, that is a positive.