I used the Eastwood High Temp Coating Factory Gray, and it came out great. This was about ten years ago, and my exhaust manifolds still look like new. The trick is all in the prep. I had them sand blasted, which I think is crucial to how they turn out. The sand blaster guy charged me $20 and they were done in one day. When I got them home, I cleaned them with lacquer thinner and a toothbrush, making sure to get in every corner, crack and crevice. I then scrubbed them with Dawn dishwasher soap and water, and blew them dry with my compressor. I then put them in my oven and heated them up to the max temp for 20 minutes. (I have one in my garage for powder baking, but you in house one will work fine as well, as long as the wife either approves, or never finds out about it). The heating up was for the purpose of releasing all the oils and grease and dirt and crap from the pores of the cast metal. After they cooled, I put three coats of the Eastwood High Temp Coating, let it dry overnight. The next day, I put them in my oven and heated them to the max temp, which was 550 on my oven for 20 minutes.
Again, this was ten years ago at least, and they still look great, and it cost me about $50 ($20 for sand blasting, $30 for Coating.)
