Over the last several years I have painted transmissions and engines with acrylic enamel, lacquer, and basecoat / clearcoat urethanes. I used ordinary lacquer type primer under all of them. All of them did fine on engines and transmissions. The lacquer was probably the least durable, that is, it chipped easily compared to the others. All of them held up pretty well against the engine heat. The only problem spot was the siamese exhaust ports on small block Chevys; the paint tends to burn there, but so does regular spray-can engine enamel. Bottom line is everything must be very clean or the paint will blister when it gets hot.