I am going to be using HP manifolds on my Coronet, at least initially, because I kind of want the original look for now. I very well may change to headers in the future if I want more power. I mention that because I believe, like many others, that you can make more power with headers. That said, some of the issues that are brought up to support one or the other seem to bring up more questions for me. For instance,
Tests - The Nick's Garage video's (the few that I have seen anyway) show the tests being done on a completed engine. The numbers are impressively in the favor of headers as could be expected. I would like to know if the engine was built (cam choice for example) with one or the other system in mind. Would the numbers come out significantly different if the engine was built with cast iron manifolds and full exhaust in mind?
Heat - I've heard (read) both sides claim a less heat advantage. I would like to know when heat starts to have an adverse effect on the engine, and which of the two systems causes more or less negative impact. Is general under hood temperature the issue, or is it area specific (burnt wires, burnt valve cover paint, etc.)?
Weight - I know that the HP manifolds for my car weigh a lot. What do good, long tube headers weigh? Is the weight difference noticeable in a street or street/strip car?