Ihave had good luck with POR15 black velvet and manifold grey. I will say that they perform much better if the engine is already run and tuned vs. first start up. Plus, if there is any old loose paint, you must get it off, or it will just lift the new stuff---like any painting product, preping is the key. No reason to sand blast which is nice, but it sure does help, and you can recoat it at anytime which is nice if you need to touch it up.