What is Reversion?
12-21-2007, 02:16 AM
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What is Reversion?
Hi All,
I have read about wild cammed motors and motors with dry pipes having reversion problems.
Is this where the exhaust has an area of low pressure under certain conditions pulling water into the exhaust then into the motor?
Also, when you say wet pipes is this where the pipe has water flowing throught exhaust where the exhaust gases exit from?
Cheers
Dave
I have read about wild cammed motors and motors with dry pipes having reversion problems.
Is this where the exhaust has an area of low pressure under certain conditions pulling water into the exhaust then into the motor?
Also, when you say wet pipes is this where the pipe has water flowing throught exhaust where the exhaust gases exit from?
Cheers
Dave
12-21-2007, 04:05 AM
#2
Charter Member # 55
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Boats with dry pipes don't have reversion. Dry pipes eliminate reversion.
There are different versions of dry pipes and most introduce a small amount of water into the tips at the end. Pretty much, the risers go all the way through the transom and the water exits there. That is what I have. Some also dump water through a hull dump fitting.
Wet pipes mix the water with the exhaust at some point before the transom.
Reversion happens with wet exhaust because of large cams with a lot of overlap and a big lope at idle. During the overlap/lope, water gets sucked backwards up the pipe. It generally only happens at idle/low rpms.
There are different versions of dry pipes and most introduce a small amount of water into the tips at the end. Pretty much, the risers go all the way through the transom and the water exits there. That is what I have. Some also dump water through a hull dump fitting.
Wet pipes mix the water with the exhaust at some point before the transom.
Reversion happens with wet exhaust because of large cams with a lot of overlap and a big lope at idle. During the overlap/lope, water gets sucked backwards up the pipe. It generally only happens at idle/low rpms.
12-21-2007, 06:17 AM
#3
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A little clarification on overlap. There's a certain portion of the engine's cycle where the intake and exhaust are both open. At higher rpm's, the inrush of intake and the outrush of exhaust continue to pull the charge in and the exhaust out so it isn't a problem. At low RPM's the piston can be travelling downward pulling the intake charge in (cylinder vacuum condition) while the exhaust is still open. This pulls a bit of exhaust back in as well. The more overlap you have, the worse this effect is. If you have alot of cam and stock Mercruiser manifolds, the point where it mixes water into the exhaust stream is very close to the engine- it can pull the exhaust/water mix back in. Some exhausts like the Gil have water dumps right at the outlet which lessens the effect. Some exhausts have no mixing at all - they dump out through a fitting at the end of the tailpipe and usually out a thru-hull fitting. This insures that reversion isn't possible.
The reason water is mixed is for a muffling effect. Without water in the exhaust, muffling becomes very diffcult- switchable mufflers would get extremely hot.
The reason water is mixed is for a muffling effect. Without water in the exhaust, muffling becomes very diffcult- switchable mufflers would get extremely hot.
