Now I am confused. According to Mercury, the purpose of the vents is to allow exhaust gases to ventilate the prop. If no exhaust gas is present (thru-hull exhaust only), how can the system work

hmmm this is getting interesting go on boys

Chris,
Do you have dedicated thru-hull exhaust only or some kind of switchable like corsa Q&Q or captains call?

Some switchable systems like the one I have(corsa) will always bleed some exhaust gases through the prop even with the valves open to the thru-hulls.

i know this isnt an answer but... I demoed a rev 4 and the holes were open. Seeing I was using thru hull I thought it wouldnt matter. The boat would barely get on plane and would hardly accellerate at low speed. I duct taped the holes off from the inside of the prop and things were fine after that. Anyone got an answer?????

I had a 27" Mirage Plus with the vent holes on a boat with through transom only. I removed the y pipe and bought the block off plate and installed it. I also removed the exhaust tube bellows because it was no longer needed and the dealer said to remove it. With the plugs out the prop would cavitate badly and could not bring the boat on plane. I think that air from where the exhaust tube (bellows) used to be was being drawn in to the prop. I dont know if the same thing would have happened with an exhaust tube or an exhaust bellows installed.

Ron

I believe rjcardinal hit the nail on the head. I was told that with out the bellows removed it caused a suction creating a great deal of drag. That being the case if the bellows is removed, the air would be sucked into the lower unit and allowing bubbles to vent across the blades. Thence letting the motor to wind up, grab some torque and goooooooo!!!

Travis you can drill any thru hub prop for the same effect. Start with a small hole and make it bigger. If it doesnt work out.. you can use bondo to plug the holes..or use a wire welder with SS wire and plug them with out any problems..

PS. I need to converse about hooking up next week.. I will be headed out on Monday morning and it looks like return on Thursday nite.. sen me a number I can reach at..

Dick

just straight through transom exhaust...

I removed all three plugs and could NOT get on plane it cavitated so badly... I put one plug back in and shazam,,, I cut my planing speed,,, this has been discussed before.. They DEFINITELY work on through hull..