lacquer doesnt stick to bare alloy, with the heat it will crack and water will get under the lacquer and make it go white, the best stuff is ACF-50 spray made for the aero trade now available for the public to buy,
good for alloy wheels too, all i do is wash the engine down with turtle wax 'wash n shine', it leaves a thin protective film when it dries, .. even a light spray with 'duck oil' (its better than W.D 40) does the trick and the grime just washes off...