Riser question.

mklearl

Petty Officer 1st Class
Joined
Apr 21, 2013
Messages
379
Putting new risers on and I'm trying to decide if I should go with the taller riser. It was recommended by Volvo to take the flappers out of the exhaust which I did but then to put on the taller risers. Which I didn't. I cant say that I've had water intrusion but I'd like to do what is recommended. The tall risers are 11.3 inches tall. From the top of my manifold to the engine compartment cover (fiberglass) it is 11.5 inches leaving me about .25 of an inch clearance. I know the risers get hot but if the water pump is working properly I can.put my hand on the top of the riser. My concern is doing damage to the compartment cover which I dont want to do. Also, if I have an impeller failure I afraid of catching fire. Any suggestions? Heat shield? Or is it not worth the risk. I'm not sure what the recommended clearance would be from the top of the riser to the engine compartment cover.
Thanks in advance.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,297
the bottom of your risers should be over 14" above the static water line of your boat sitting when loaded.

If you have an impeller failure and you overheat, you did not do your recommended maintenance (impeller replacement) and you were not watching your gauges.

your rubber exhaust melts/burns at 250 degrees. fiberglass is good until about 300 degrees, so your exhaust will catch on fire quicker than your hatch.

go back to your static water line measurement, if your already above 14" with the shorter riser, then you are good, if not, add the taller riser.
 

mklearl

Petty Officer 1st Class
Joined
Apr 21, 2013
Messages
379
Measuring from the bottom of the riser like where it meets the manifold or bottom of the exhaust port where water intrusion can first occur?
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,297
no, measuring the elbow for the highest point of the bottom of the elbow where it turns down for discharge

start at the top of the gunwale, measure down to the water line - this is measurement A
then measure from the top of the gunwale to the bottom of the elbow where it starts to turn back down - this is measurement B

A-B is your riser height over the static water line.
 

mklearl

Petty Officer 1st Class
Joined
Apr 21, 2013
Messages
379
One last question. If I go from the previous standard riser to the taller riser will I also need to replace the y pipe? I've read bulletin p-25-1 but it really isn't making much sense. My concern is that by raising up 3 inches the riser exhaust wont align with the y pipe. I see in the bulletin that the Kits are specific to the y pipe but I'm not sure what kit to get. I have a DP-SM outdrive.
 
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