I/O exhaust question

Milkmaster

Cadet
Joined
Sep 20, 2007
Messages
15
I am used to a inboard tow boat that has the exhaust ports in the hull of the boat. It just occured to me that I didn't see those ports on the rear end of a 4.3 Mercrusier package. Where are the I/O exhaust ports found?

An interesting reason for me looking in the first place. The boat I was looking at had a new lower unit. The owner was telling me that the insurance had just replaced it. I asked him if he ran over something. He said "Heck no!" Someone stole the lower end off his I/O while his wife were in a resturant eating after being at the lake all weekend. They had parked the boat in the resturant parking lot on the way home. First time I ever heard of such a thing. Is this common? Is it something I should worry about when parking my boat while I go potty at say a gas station? Are the lower ends that easy to remove?
 

jddenham

Petty Officer 1st Class
Joined
Aug 8, 2006
Messages
393
Re: I/O exhaust question

Some go thru the lower unit and out the prop hub like an outboard.
 

j442w30

Petty Officer 1st Class
Joined
Jan 9, 2007
Messages
264
Re: I/O exhaust question

The exhaust travels out of the engine through the manifolds into the Y pipe, through the exhaust bellows down through the outdrive and out through the prop. If you run it on muffs you will see the exhaust exiting through the prop.

Regarding the stolen outdrive, it takes about 10 minutes to get the outdrive off, probably less for someone experienced, easily something somebody could do while the owners were eating dinner at a restaurant. You can buy special locking nuts that replace the standard nuts that hold the drive onto the bellhousing. I believe Mcgard makes them. It's cheap insurance if you're concerned about it.
 

PhatboyC

Petty Officer 1st Class
Joined
Sep 28, 2007
Messages
258
Re: I/O exhaust question

Just to ad to the excellent definition above. It's called thru-hub exhaust. I just learn the term while searching last week on Volvo's Duoprop. The Duoprop also routes exhaust through the cavitation plate. Which I find to make richer sound when coming out of the whole. I/O can also have a thru-hull exhaust like the ones your used to but the sound these makes has a love/hate reputation.

Here is link with some diagram of other types of exhaust. (No duoprop tho.)
http:// www.keypart. com/Marine/Propellers/HubExhausts. aspx
No direct linking please, just referals.
 
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