Reason for snailbacks?

[Nordic78]

Can anyone explain the reason for the snailbacks on log style exhaust and is there other options that are less restrictive. I cant change my headers:confused: because of my engine cover so I am looking for ways to increase flow.

[Rexone]

They are there to prevent the backflow of water through the exhaust ports in boats (typically jets) where the engine is mounted low (they are a damlike device).
Normally engines that are mounted higher, (vdrives) won't be equipped with them and will have angle elbows of some type.
Flappers are meant to stop the surge. Snails assist with that but are also a water dam as flappers do not offer a positive seal (aren't meant to).
The way around these horsepower robbers along with the logs is to switch to a center rise top outlet type exhaust manifold and S pipe arrangement. They are more efficient by design than logs and don't require snails because of their height.