When I was young & cars were carbeuretted, the first performance upgrade (& cheapest) was to put on headers & paint them w/ VHT paint. Nodalos was the go to guy when it came to performance exhaust. As I recall, the good ones were a 4 to 1 & the pipe diameter was configured. You can’t have them too large as a little resistance is needed. If you are running a stock engine, it may back fire, a sign that you need a little resistance & your timing is a bit off. It may also help to port & polish the intake manifolds for additional hp. Performance engines, those running double barrel twin side Webers with racing cams are usually the ones with a healthy back fire. Those were the days.