Maximum exhaust riser height?

[500dollar744ti]

I have a set of the mercruiser silent choice exhaust cutouts that I want to install. My boat has an integrated swim platform that is exactly at the same height as the current exhaust riser outlet.

Can I space the riser up another 4-6 inches so I can install the thru hull exhaust above my swim platform where I can cut holes without having to go through the thick wood of the transom?

My engine compartment is crowded as it is and putting the thru hull exhaust below the swim platform would require both cutting through the transom and rerouting a lot of wiring and hydraulics for the trim tabs.

I am asking is there a maximum height for the exhaust riser above the manifold? I tried searching for mercruiser engines with something like 8 inches worth of exhaust riser and couldn't really find anything.

In theory how high could you possibly have a riser before it becomes a problem, if it can become a problem?

 

[Bt Doctur]

There is a minimum height of 13 inches above the water line to prevent water ingestion but I have seen 6 and 9 inch

 

[500dollar744ti]

I understand the minimum, it already meets that requirement as it is now. I want to make the riser even taller with spacers, is there any reason why I shouldn't make the riser even taller? For example, lets say I wanted to make the riser 24" tall, obviously unrealistic and unnecessary, but could that be done as long as the water hoses are long enough and everything bolts up properly?

As long as it is 13" above the water line, it doesn't matter how much taller the riser is beyond that, correct?

 

[alldodge]

I understand the minimum, it already meets that requirement as it is now. I want to make the riser even taller with spacers, is there any reason why I shouldn't make the riser even taller? For example, lets say I wanted to make the riser 24" tall, obviously unrealistic and unnecessary, but could that be done as long as the water hoses are long enough and everything bolts up properly?

As long as it is 13" above the water line, it doesn't matter how much taller the riser is beyond that, correct?

There probably is a max but most anyone will not get into this area without changing from a stock pump to a 3 stage type. The factory sells 6 inch risers so lets say an additional 6 inches should be of no issue. Now if your going above that, its probably OK but need to make sure the seawater pump can pump that high at volume without loosing cooling ability.

You could call Merc Tech support and they should be able to answer it.

Some high performance boats use tractor pipes

 

[achris]

Merc (and I suspect a few aftermarkets) make a 'spacer', usually in 3" and 6". They are called risers... The part of the exhaust that bolts onto the top of a riser is the elbow.... But if you already have risers, and you need more elevation, then yes, you can stack risers....

Chris....

(BTW, you'll use the through-hulls about twice, maybe 3 times, then you'll leave it on through-prop... )

 

[Bondo]

My engine compartment is crowded

Ayuh,.... Do you have the space above the motor, but below the motor box cover,..??

Will the exhaust pipes be at a Downhill angle, after ya put the riser extensions on,..??

 

[Scott Danforth]

I wouldnt install them above the swim deck. your swim deck will be covered in soot and goo

get side exit tips and install them that way

 

[500dollar744ti]

Ayuh,.... Do you have the space above the motor, but below the motor box cover,..??

Will the exhaust pipes be at a Downhill angle, after ya put the riser extensions on,..??

Yes, there is enough space. I have to install spacers in the risers so that I can get a downhill angle, yes.

I wouldnt install them above the swim deck. your swim deck will be covered in soot and goo

get side exit tips and install them that way

That is something I didn't think about, maybe I can do side exit. I have side exit hardware already but I'll need to move a lot of stuff around to accomplish it.

 

[Scott Danforth]

so move your stuff. a few screws and some 5200 and your done in a few hours