Reversion is the vacuum pulses created in an engines exhaust system when the camshaft specification is so large that it leaves the intake and exhaust valves open simultaneously. As the engines piston travels on the downward stroke with the intake valve open for a split second it sends a vacuum pulse up the exhaust system and the vacuum grabs the solid moisture properties in the exhaust system and pulls them back into the engine.

Rarely does a stock engine ever experience this due to the camshaft nature being smaller and the lobe separation so tight. It is the change to a high performance camshaft that cause this. The larger the cubic inch the engine the worse the problem. The larger the camshaft with more duration the worse the problem is.

Automotive engines don't have this issue because there is not water in the exhaust.  Add big cubic inches, a large overlap camshaft, wet exhaust; and the problem only gets worse.  If you use an automotive style camshaft to build your marine engine, you're in for trouble.  

The automotive camshaft does not take into account the presence of water in the exhaust.  If you use a automotive style camshaft with a duration greater than stock, the engine will pull water back from the exhaust, making your engine a 8 cylinder water pump.

For in depth modified engine applications you should call us to discuss possible options and parts selections