Professional coatings is an involved process and the product they use is superior. It starts with baking your headers to remove any oil/contaminates. Next they media blast your headers to clean and prep the surface for proper adhesion. After they will coat your headers and then put them through a high heat bake cycle effectively curing it permanently. And if you choose the silver ceramic finish they put your headers into a giant media polishing machine and they come out all pretty and shiny. A finish that could never be replicated with a spray can job.
Now with a proper prep and curing process a spray can job can be somewhat effective. You'll have to media blast your headers. Paint them with about 3 or 4 light coats (I prefer Dupli Color or VHT Flameproof Coating). DO NOT USE ENGINE PAINT..! Let them air dry for at least 48 hours. And then install them and run your engine to cure them. Now when you run your engine you'll want to start with a quick 30 second warm up. Let them cool off. And then follow that with a 1 minute warm up. Let them cool. And then a 5 minute warm up. Let them cool. And finally a full warm up of your engine and let them completely cool for a day.
In the end it boils down to cost and long term durability. Prfessional will run you around $400-$600. Do it yourself will cost around $150. That includes paying someone to blast your headers.
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