Exhaust manifold / riser question

[cm5408]

i have a manifold and riser like the one shown below. i am in the process of running a thru hull exhaust and i want to know if there is enough rise and degree of angle on the riser to prevent water from flowing up the exhaust line and into the manifold (the tube for the exhaust extends about 12 more inches before the transom & the tips are right at the water line). Or, do i need to try and find a spacer to raise the riser higher into the air? the exhaust tips do have a flapper on them, but in reallity how well does that flapper work in keeping water from flowing in?

 

[calwldlif]

Re: Exhaust manifold / riser question

Looking at those, with the Volvo castings
I shudder to think the cost.
They are pretty though.
I can't add to much to your question other than
the higher the top is the better

 

[cm5408]

Re: Exhaust manifold / riser question

yes, i am sure that if i ever needed to replace them, dollar signs would be flowing.

i just found a picture of them online to show what i currently have. i wasnt able to get a good picture while the manifolds are still on the motor.

any help is greatly appreciated

 

[Reel Poor]

Re: Exhaust manifold / riser question

If your thru hulls are that close to the water you will have to be reeeeeeaaaaal careful when launching your boat as that will be one of the most likely opportunities for water to intrude into the engine, that and waves hitting the back of the boat. Even with taller risers. :%

The higher you can mount the thru hulls the better.

 

[cm5408]

Re: Exhaust manifold / riser question

from the very end of the riser (look at the one on top for illistration) to the inside wall of the transom is 12 inches. the exhaust hose will come straight out of the riser following the riser's degree of angle. the exhaust tip's lowest most edge will be about an inch to two inches lower than the exhaust ports from the heads into the manifolds, giving what looks like from the tips lowest part to the lowest turn of the riser (where if water were to flow over into the manifolds) a rise of 7 - 9 inches. opinions please???

does any of that make sence?

 

[cm5408]

Re: Exhaust manifold / riser question

a lot of people looking...
please, any thoughts will help me

 

[JasonR]

Re: Exhaust manifold / riser question

I have a inboard with about 8 feet of pipe between my tips and risers. The only thing between them is the flappers, mufflers and about 2.5 feet of rise. All ski boats are this way. I guess I'm just no seeing the issue.

 

[Reel Poor]

Re: Exhaust manifold / riser question

When I was researching putting thru hull exhaust in one of my boats I want to say there was a minimum rise of 12 to 15 inches above the static water line of the boat. PLEASE,,,, this is not gosple, I've been trying to remember.

 

[paulie0735]

Re: Exhaust manifold / riser question

It depends the type of boat you have and how its stored. I have a ski boat with much less total rise than you do I run log manifolds with no risers at all just flappers on the outlets. Been this way for 23 years and nearly 3,000 hours. Engine also runs an aggressive performance cam with way to much overlap (supposedly!) for marine use. Much of the talk is re 'worst case scenario' stuff, my setup would be a disaster on a cruiser that sat in the water all its life, but in my case my setup is actually ideal. Position your exhaust outlets so they are just under the water line, at any speed above idle they will than come clear of the water. Good luck.

 

[Cptkid570]

Re: Exhaust manifold / riser question

I don't mean to hijack the thread, but what exactly are log manifolds? What applications can they be used on? Where does the raw water drain out?

 

[cm5408]

Re: Exhaust manifold / riser question

When I was researching putting thru hull exhaust in one of my boats I want to say there was a minimum rise of 12 to 15 inches above the static water line of the boat.

are you talking from the static water line to the top of the riser? to the lowest bend in the riser (were water would crest over)?

 

[Reel Poor]

Re: Exhaust manifold / riser question

When I was researching putting thru hull exhaust in one of my boats I want to say there was a minimum rise of 12 to 15 inches above the static water line of the boat.

are you talking from the static water line to the top of the riser? to the lowest bend in the riser (were water would crest over)?

To the lowest point in the riser, were water could flow over into the manifold. Instalation at this hight also recommended flappers.

 

[cm5408]

Re: Exhaust manifold / riser question

i have 10 inches from the water line to the lowest part on the inside of the riser, the exhaust tips have flappers.

 

[rebars1]

Re: Exhaust manifold / riser question

Kind of late reply, and you've probably already solved your situation, but I have the same manifold/risers.However, they have a 2" spacer block between them. The 2" spacer blocks used to be offered by Volvo as a kit. I think they may still have it in a 3" version.