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Old 03 May 2006, 09:17   #1
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mercury prop vent plugs

after a bit of advice and guidance here

i have a set of solid and a set of plugs with holes in them that fit on the mercury prop, as standard it came with the plugs with holes in and i am wondering what performance difference i would get by fitting the solid plugs into the prop
can anyone advise which is probably best, would i get more cavitation with the plugs with holes or vice versa, only kept as standard so far and going to swap plugs over this weekend but wandering what to look for

ta
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Old 03 May 2006, 09:49   #2
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Hi Hugh
Had the same when I bought a SS prop, had great acceleration without the plugs and once I'd fitted them, it made no difference at all !
I think the theory is that with plugs in it lowers acceleration and improves top speed.
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Old 03 May 2006, 10:53   #3
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The purpose of the plugs it to prevent the engines on heavy boats from bogging down and then not being able to get the boat up on the plane.

Blocked them up on the Searider - no detriment to performance

Blocked them up on the Scorpion - no detriment to performance - although it does require a bit of effort to get the boat up when there are 6 or more people on board. Not sure I can be bothered to take them out to try though!
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Old 03 May 2006, 13:14   #4
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i think i will use the blocked up plugs and see how i get on then. Thanks for the replies so far
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Old 03 May 2006, 14:03   #5
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Its called the performance vent system. There are 4 different sizes of plug available. On accleration exhaust is drawn out of the vent holes behind each blade. When the next blade strikes the areated water, less force is required to push through the areated water vs solid water. This allows engine revs to rise more rapidly. Once at on plane speed, water flowing over the vent holes seals the exhaust in, allowing the prop to operate in solid, non areated water. By varying the size of the exhaust hole, the rate at which engine rpm rises can now be controlled

So there you have it, slow acceleration or sluggish performance, increase the hole size Whereas over ventillation, will cause over revving cavitaion etc

All related to pitch load etc
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Old 03 May 2006, 15:26   #6
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cheers for that, great explaination

have fitted the full blanks as dont need any help getting on the plane so will try with the holes filled in and see how that goes
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Old 03 May 2006, 16:49   #7
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Do all props have these? I have a Solas 19" 4 blade for my suzuki - will it have them? Something else to fiddle with if it has.
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Old 03 May 2006, 17:16   #8
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No, not all props have them. The QS Laser 2's do. Hughjus, The Mercruiser Alpha One leg will run the same prop as the larger Merc/Mariner outboards but, the inboards have more power and heaps more torque, therefore the vents can be plugged. On a 135hp outboard running the same prop, it may to leave them out to get a bit of help from the 'venting'. As you're running max hp on your hull, you shoudn't need any help at all!
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Old 03 May 2006, 17:16   #9
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probably not


only modern high performance engines less that 15 years old have them


Quote:
Originally Posted by codprawn
Do all props have these? I have a Solas 19" 4 blade for my suzuki - will it have them? Something else to fiddle with if it has.
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Old 03 May 2006, 18:35   #10
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Here is the list that have them, I am not a saddo dealer by the way LasreII, Trophy Plus, and Tempest, Hehe


Awaiting flame ...... hmm
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