See us on:
Visit CP on Facebook Visit CP on Twitter Visit CP on YouTube
Is your boat in the gallery?
Image Gallery  
Instructions & Guides:
Instructions  
Find Parts by Mercury Model:
OEM Part Finder  
What's on sale today?
Sale Specials  
What are you looking for Today?

Need Help? Call Us:

1-800-225-9871

Outside the USA? Call 707-585-9871

REVERSION? WHAT IS IT?

WARNING* WARNING* WARNING* 

Read carefully before you purchase! Performance modified engines are prone to "reversion":

What is water reversion?

In layman's terms its the engine producing vacuum in the exhaust and drawing the engines exhaust cooling water back in to the engine causing catastrophic damage. For the sake of details  here's another look at it. On larger duration camshafts with increased intake/exhaust valve overlap at low engine (idle) running rate the exhaust pulse is sucked backwards towards the engine flowing the engines exhaust cooling water backwards momentarily.

On higher horsepower applications with more aggressive camshafts duration or overlap of the camshaft design phase that the piston is pushing out the last of the exhaust gases as it reaches top dead center. The intake valve opens and the exhaust valve continues to stay open during this point of overlap   at low engine  rpm rates (idle) the intake starts its downward stroke and the exhaust valve is still not closed.

As a result the piston pulls from the intake and exhaust valve simultaneously causing the exhaust gases to reverse. Not a problem until you add water into the exhaust stream. This exhaust reversion can be severe enough to stall the engine, add water to the oil, rust the exhaust seats, even hydraulic the engine breaking major engine components. This effect only happens at idle, but remember that during shut down the engine encounters the greatest reversion. 

For this reason guidelines for camshaft selection or use should be discussed with one of our technical experts. Many facets play into the severity of this situation. Things that magnify this. These examples are just guidelines. Increased cubic inches, valve size, exhaust valve timing, etc., All will have an effect on reversion. Keep in mind its inherent for a marine exhaust to show signs of moisture inside due to the characteristics of hot exhaust being cooled by cooler water. This commonly causes condensation not to be confused with reversion.

Your Options? 

Extended "dry" tail pipes where the tailpipe is water jacketed all the way through the transom to the end of the exhaust..THIS Substantially reduces if not eliminates reversion.

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