Huge exhaust question


Old 05-30-08, 06:58 PM
Thread Starter
Join Date: May 2008
Posts: 9
Unhappy Huge exhaust question

How can an inboard motor expell exhaust gasses efficently thru an outdrive ? Theres like two pipes running into a small porthole on the outdrive unit....and usually thru mufflers first...... And then into the water? wouldnt the exhaust above the water line thru low restriction muffs work much, much better? What were they thinking? Am I alone here on this? Also while polluting the water with exhaust? Sound cant be all this was about? cum mon !

Last edited by mopar craxy; 05-30-08 at 07:00 PM. Reason: misspelld
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Old 06-01-08, 06:09 AM
Join Date: Aug 2005
Posts: 2,268
Sound is, in fact, the major reason for exhaust expelling through the prop hub on an inboard/outboard. Go stand around the marina for an afternoon and notice the difference in boats with through hub exhausts and through hull exhausts/over transom exhausts - it's pretty major. Most folks don't want to have to yell over the sound of their engines (noise pollution) Boats don't have mufflers, but rather water jacketed exhaust manifolds that preheat the water going into the engine, and cool the exhaust manifolds to avoid a potentially explosive condition (red hot manifolds). In addition, the forward motion of the boat actually creates a negative pressure at the hub, assisting in the movement of the exhaust gasses. As far as polluting the water - well, you can expell gases into the water or into the air - neither is good for the environment.

On the other hand, there are those of us who prefer the throaty sound of a big block exhaust through the transom, above the water line - (All my boats are of that design).

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