Mirage SS prop plugs

Pirate Lady

Well-Known Member
Jun 2, 2020
7,574
Chesapeake Bay, Middle River
Boat Info
Sundancer 250 ‘91
Engines
7.4 Bravo 1
Mechanic told me I should have plugs in the holes of this prop. Ran all last year without. Anybody know the uprise and where to buy? Pic attached. There are 3 holes, one at the base of each blade.
 

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Vent holes. The ventilation lets your prop slip to get into the power band. Don't need that on your average boat, more of a go-fast thing running a tall prop.
 
I have some I'm not using. If you DM me your address I can mail them to you.
 
The mechanic said the holes are for an outboard, said something about back pressure, I see lots of these rubber plugs on amazon, all different sizes and shapes, how do I get right ones. Also boat launched today. Won’t be able to put in til mid summer haul to pressure wash. Since it ran all last year without plugs, any problem with letting go til July? Is this critical stuff?
 
It's not critical. You can run without the plugs. You'll have more prop slip at lower speeds without the plugs in.
 
It's not critical. You can run without the plugs. You'll have more prop slip at lower speeds without the plugs in.
Will it get on plane faster with plugs in? Honest god, first time in 30 years I never encountered this before. I have spare mirage prop with no holes but it needs to be recon badly before use.
 
I got the address. I should be able to mail them out in a couple of days. It should get on plane faster with the plugs in. The holes aerate the water allowing the 2 stroke outboards to spin up into their higher rpm band before the prop starts to get a good grip on the water. Your 454 doesn't need to spin up before getting a good grip on the water.
 
There are different sized plugs in the PVS system (various hole sizes) to adjust the amount of exhaust gasses released to allow more/less slip, as mentioned. You kinda don't know which way would be best for your setup without trying. It's a trial and error thing. I had a 210BR with a 350 and found that the middle sized holes was best for hole shot and acceleration. I did multiple, timed, 0-30mph and "on plane" trials, trying to keep my stopwatch timing as true as possible. Since I did about 5 runs with each hole, I was able to pretty reasonably judge. That said, while there was a difference, it wasn't a night and day difference, either. I suspect with your setup, there will be even less difference.

Once the boat is going faster, the gasses no longer escape through the holes due to the water streaming over the prop and the negative pressure created behind the prop to pull the gasses out.
 
Mechanic told me I should have plugs in the holes of this prop. Ran all last year without. Anybody know the uprise and where to buy? Pic attached. There are 3 holes, one at the base of each blade.
454 Bravo one, you won't notice any difference
 
Plugs are packaged and ready to ship. I'll mail them off Monday.
 

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