Running Open Headers

[Big Blue 72]

I won't get into a big long history of what's been going on, but my friend is finishing up a 390 rebuild. Gonna do the break-in start up this weekend. He has new ceramic coated headers but the directions warn not to use them during the break-in because the intense heat will cause them to discolor. Because of the way things are set up he plans on, and has to run the old open headers for the 20 minute +/- break-in period and then switch over to the ceramic headers. Correct me if I'm wrong, but I thought running open headers carries the risk of damaging engine components, especially if you're starting the engine for the first time. He's says it would if it were really cold and the cold air were allowed to return towards the engine but he feels it'll be fine. I still think I'm right and wouldn't take the chance. Anyone have any experience with this?

[Dragon]

The headers will be so hot after the 20 minutes that the exhaust valves won't get any cold air. When I break in an open exhaust engine the 1st run is 5 minutes then an oil inspection. Then longer runs none less than 15 except for problems. We cap the exhaust on the first run with a rag. After that the headers are too hot to allow cold air to get back in. Your biggest worry is not how long but what happens in the 1st few minutes. No blipping the throttle so it does not suck back into the headers and no high rpm. I never let mine idle less than 2000 for the first 20 minutes of life and no free revs above 4000. After that Look out.