To confuse things even more is when picking a cam or intake the manufacturer posts an RPM range on them. Like this 1500-5500 RPM basic operating range. https://www.summitracing.com/parts/cca-cl12-210-2 With all my cam swapping and testing I found that upper RPM is where the cam will make Max HP in the comp cams line of cams. I run that above 268H and 5700 RPM is where I make max HP with decent flowing heads. In a 350" Stock smogger heads you can be down 1000 RPM where the peaks come in. Now you normally shift 500-700RPM past Peak HP that puts the above 268H at a shift point of 6200rpm. But junk heads that do not move air well you may be shifting at 5200 or 5500 rpm. leaving power on the table. "Plugged up" exhaust system will hinder power also. or a carburetor that does not meter fuel well. There are ways to check those things.. Vacuum gauge is a great tuning tool to find things out. So many variables.