I used to apply Eastwood's exhaust manifold coating to the exterior of the heads, along the exhaust runners. That delayed the paint burning off, discoloring, then rust starting.
A few years ago, I was applying "cold galvanize" zinc-rich spray primer to a part. I had that part resting on the firebox of my smoker. Awhile later, I fired up the pit and cooked for about 15 hours. Although BBQ paint and other high temp paints always burned off the firebox, I noticed that the zinc paint had held up quite well.
Since then, I've used the cold galvanize as a primer on several engines (it seems to adhere better than regular primer) then apply the engine paint. I have around 1,200 miles on my own 455, since I last painted it. The exhaust runners have turned white, but no rust has appeared.
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'73 T/A (clone). Low budget stock headed 8.3:1 455, 222/242 116lsa .443/.435 cam. FAST Sportsman EFI, 315rwhp/385rwtq on 87 octane. 13.12 @103.2, 1.91 60'.
'67 Firebird [sold], ; 11.27 @ 119.61, 7.167 @ 96.07, with UD 280/280 (108LSA/ 109 ICL)solid cam. [1.537, 7.233 @93.61, 11.46 @ 115.4 w/ old UD 288/296 108 hydraulic cam] Feb '05 HPP, home-ported "16" D-ports, dished pistons (pump gas only), 3.42 gears, 275/60 DR's, 750DP, T2, full exhaust
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