Reversion, cam limits for common setups.
 

So where would the cut-off point be with any of the common power packages and exhausts? And power limits with the standard exhausts? Everybody is always asking what is too much with my 330 or my 365 mag or the L29 with 496 Gils, etc...Maybe we can get most of the answers in one place.

First off I am not knowledgeable on exact numbers for that but I can tell you it can be very boat dependent. ESPECIALLY with molded in swim platforms.

Chris

I have a Merc 525sc. I am running EMI thunder Exhaust. The cam I will be using is Crane 134561. Theres a few on here with that cam and no reversion. Ill know for sure in a month or so.

A lot of factors goes into a reversion issue what are you trying to do? how high get you get your tailpipes .lenght of pipes are a few factors

Watching with interest. Thinking about next build and wondering where that line is for Stainless Marine manifolds. How much more would going dry close to tip give you?

if you look at the cam,s that merc uses with the black engines you will see that the duration,s are short and the lsa is wide.the mix of water&exhaust gas in the tailpipe[usually a 4in rubber hose]is the problem.the best way to avoid reversion is to remove the water from the exhaust flow.that is why aftermarket exhaust manifolds&dry tailpipes exist.any time you put a cam with a tighter lsa or much more duration with wet exhaust you increase the chance of reversion,period.i hope this helps people to understand reversion.edit in,when you add duration and tighten the lsa the overlap period is longer,now it is trying to suck some of the exhaust[and water]back in.this is reversion.to much and it can ruin an engine quickly.

One notable exception is the cam most utilized Merc SBC, it has a 109 LSA, but very short duration (GM 395 cam).

From my reading, ignition timing plays a role in reversion too. A motor running 11* of timing at idle will have less vacuum than a motor with 28* of timing at idle, increased vacuum increases the reversion. I assume if you have a cam that's on the verge of reversion, running less timing at idle will help.

if you have a reversion problem changing the ignition timing won,t fix it but a dual plane manifold can help.

because the duration is so small the 109 lsa is ok.