Volvo Penta recommends removing flappers

[harojs]

[Q] Is there a formula to determine if risers sit high enough that removing flappers on older VP models per VP service bulletin will not cause boat to sink?, or have undue backflow issues?

John

1969 24ft Tollycraft w/ VP 5.0L SX retrofit

 

[Lubak572]

Following......

 

[Thalasso]

If yours is newer then 1999 it has no flappers.
Volvo stopped using them that year

 

[Scott Danforth]

and Volvo didnt use them prior to about 1994. it was only the JV drives with the thru-prop exhaust

the magic formula is that the elbow is higher than 14" above the static water line. if it isnt, then you need to ad risers.

 

[Lou C]

Also Volvo added one way check valves to the elbows and this helps eliminate vacuum in the exhaust system that’can pull water back up the exhaust into the cylinders,