Older Mercruisers had the exhaust flappers at the bottom of the Y pipe. The
Log style can be converted to center rise in most cases.
JIMinFL

"MikeT" wrote in message
...
I have a Thomson, 79 350 260 HP with a newer 86 Alpha on it. My problem is,
the water occasionally gets into the head area, which we all know is not a
good thing. It uses the older log style manifold with 3 in rear risers
with
a rubber boot adapting to 4 inch Y tube going to the outdrive.

Now the question, where on this set-up do the anti-backup flappers go that
prevent water from backing up into the exhaust manifolds, and ultimately
into the heads? Someone said something about them dropping into the Y tube
where the rubber boot adapts to the risers.

I have been getting away without them only by being extremely careful, but
fishing the great lakes in swells makes being careful difficult, and my
heads cannot take to much more water in them.

Thanks folks.