dyno

OK we have been talking about cam choices for a while and one of the big factors is always reversion...I have EMI fanifolds and Merc silent choice now but the silent choice is going away!I'm going to switchable mufflers in the spring. Is there ways of limiting the ammount of water runnig through the exhaust to minimize the possibility of reversion? I think Tinker did it with his maybe he can enlighten me.....pictures would be good Steve.

dyno

ttt

sgrady

Too Old has it down !

Tinkerer

Pictures wont show what I did.
I have 1992 engines and I removed the cover off the thermostat housing and then removed the shield that holds the thermostat down and then drilled two 1/4 inch holes behind the shield into the area where the water inlet hose enters the housing. With these bypass holes the cold lake water will bypass the thermostat and go right out the exhaust hose ( hose that goes to the bottom of the manifolds ) This way the exhaust gets water even when the engine is cold so that the rubber hoses don't burn up.
I then run the hoses that went to the top of the exhaust out the back of the boat. I built some dumps that spray this water onto the top of the drives to cool them since it is almost lake temp. I don't have any chalking on my drives and I don't have ugly drive showers.
My exhaust runs very dry and is VERY loud in open mode. ( I have silent choice )
You can adjust the temperature of your exhaust by the size of the holes but no smaller than two 1/4 inchers.
Do not drill the thermostat or your engine will run cold at idle and low cruise.

dyno

Steve the question then is do you think this will help avoid reversion?? will it allow me to run a bigger cam with my Emi exhaust?

liquid lounge

I have oft contemplated a reversion free hp exhaust system for boats...somthing along the lines of the old "Baja Bug" exhaust, only taller....the extended into the air pipes would have a Big Ed Daddy Roth look and could double duty as a ski tow, grab handles, even bimini framing. I've yet to do a patent search, however.

Offshore Addiction

ya,keep your lobe separation back on your cam choice!

Viper31

I've often wondered what effect, if any, mufflers have on reversion. Any comments?

jpclear

It has always been my understanding, (and I'm sure that someone will tell me that I understand wrong) that the volume of water mixing with the exhaust (especially at speed) has very little to do with the water ingestion problem called "reversion". Camshaft LSA (Lobe Separation Angle) has a GREAT DEAL to do with it. The less LSA you can run, (like 110 deg. or less) the more HP you can make BUT the more reversion you are subject to; especially at idle. So dry pipes with a separate cooling water dump is the best answer as long as you don't need the water for silencing purposes. Going to a cam with a 113 or 114 deg. LSA will allow you to dump water in and even use a switchable exhaust divertor system and idle all the way out the channel without reversion worries. The downside is, of course, that cam doesn't make as much HP. Now you got decisions to make. Luck!! --- Jer

Tinkerer

The only time you will have a problem with reversion is at low RPM.
The drier that you keep your exhaust the lower chance you will have any reversion.
Reversion happens when at low rpm the piston is moving back down but the valve is not yet closed and the intake valve is starting to open. This can cause reverse air flow from the exhaust into the engine.