What is the Purpose of a Loop in the Exhaust? Honda Grom Zoom loop exhaust

It's for tuning the length of the pipe to better suit an application. People say it's for "back pressure" but don't know what that means. It's not for increasing pressure in the exhaust, it's for reducing pressure at the exact moment the exhaust valve opens. Thereby creating a little vacuum effect to suck gasses out of the cylinder. This is why NA race engines want equal length headers and also why EXUP powervalves were developed. The thing is, this effect only really works in a narrow rpm range and where in the rpm range is determined by the pipe length. A rough rule of thumb is shorter pipes, higher rpm, race bikes. Longer pipes lower rpm, more usable power. Link to that DB killer I used https://a.co/d/1xRYNia Video Sponser : https://www.evokestudio.io