big block exaust a body

On a stock motor, they probably help. Anything past a carb change and they start to fall off but for the PITA aspect of headers in a big block A, they are golden, especially when you can get a pair for under $100. I had hi-pos and went to a Pro-parts header and there was a noticeable difference but had to do hours of work and welding to get the Pro-parts to fit my custom install.