drilling vent holes in SS prop

[phatmanmike]

hello, i know the theory of drilling the small 1/8th or so vent holes between the blades to let the motor rev up quicker and take off faster in gear. i have done this with my inline 6 115 on a 21p aluminum prop.<br /><br />but....<br /><br />now i have a 1989 mercury 90hp 3 cylinder and a 17p SS prop, a rapture , i believe is how you spell it.<br /><br />i really liked the way it pinned you to the seat and took off really quickly without affecting top end speed .<br /><br />i wanted to do the same with this prop, but didnt know if it was advised or disadvised because its SS versus aluminum.<br /><br />any ideas?

 

[Mercathode]

Re: drilling vent holes in SS prop

Should work great. My 200 Mariner had a 25" Lazer with ports and it had a heck of an hole shot! Bleeds a little exhaust around the blades to give a little RPM bump!

 

[bb_ed]

Re: drilling vent holes in SS prop

Hello,<br /><br />I'm new around here but I have found the Search function EXTREMELY helpful. Here is a thread I found on your topic using it.<br /><br /> Prop Drilling Thread<br /><br />Not much development has been done on aluminum props so you are probably better off starting with a stainless one. Some racing props are even made from pretty exotic alloys.<br /><br />Ed.

 

[walleyehed]

Re: drilling vent holes in SS prop

Mike, from the very front of the outer edge of the hub, go straight back to the point the blade leading edge meets the housing. On the aft side of the blade (Behind the blade in relation to direction of movement), Measure 5/8" from the point the blade contacts housing, 90 degrees to the prop shaft plain which would be parallel to the hub front and rear. Mark that with a medium tip marker. Do all blades that way, then before drilling, turn prop in a direction that you can verify the drilling will not coincide with the inner webs between outer and inner hub. If that looks good, take a center punch and make a small mark in the center of your marker spot. Start with a 1/8" bit. Drill as straight as you possibly can. Test prop before going any bigger. You may need to go 5/32" but not much more if any.<br />If you want a good picture to follow with demensions, email me ktsander@st-tel.net

 

[Chris1956]

Re: drilling vent holes in SS prop

Mike, I bought a Rapture prop some years ago for my Mercruiser. It came with vent holes, so I guess I thought all the Rapture props did.<br /><br />Ironically, I plugged them up. I did not think the venting would be an advantage on the 4 cycle torque curve.

 

[C-RAVEN]

Re: drilling vent holes in SS prop

the diagram link was not very clear<br />is there a better diagram to refer to?<br />also, will i have problems drilling my stainless prop with a standard drill bit?<br /><br />Thanks

 

[bubbakat]

Re: drilling vent holes in SS prop

If you guys want it I have the flyer put out by omc on drilling those holes. Just leave e-mail addy.

 

[C-RAVEN]

Re: drilling vent holes in SS prop

Originally posted by bubbakat:<br /> If you guys want it I have the flyer put out by omc on drilling those holes. Just leave e-mail addy.

 

[C-RAVEN]

Re: drilling vent holes in SS prop

please email to scottc@sheret.com

 

[bubbakat]

Re: drilling vent holes in SS prop

C-RAVEN you have mail

 

[phatmanmike]

Re: drilling vent holes in SS prop

 

[lakelover]

Re: drilling vent holes in SS prop

Originally posted by bubbakat:<br /> If you guys want it I have the flyer put out by omc on drilling those holes. Just leave e-mail addy.

karryinon@aol.com <br /><br />Thanks.

 

[KCLOST]

Re: drilling vent holes in SS prop

Be careful,,,, If it's got a great hole shot now, you won't need any holes...<br /><br />Start small,,,

 

[walleyehed]

Re: drilling vent holes in SS prop

I guess my previous post shows up only on my computer...

 

[phatmanmike]

Re: drilling vent holes in SS prop

hey lakelover, look up

 

[oneoldude]

Re: drilling vent holes in SS prop

Originally posted by bubbakat:<br /> If you guys want it I have the flyer put out by omc on drilling those holes. Just leave e-mail addy.

Sure do!<br /><br />oneoldude@THORNcomcast.net just pull the THORN<br /><br />Thanks

 

[BassCat73]

Re: drilling vent holes in SS prop

This is an interesting subject. I'm curious if this modification would work on my motor. I have a '92 Mercury 115 outboard. It's in storage right now, so I cannot look at it. But, I think it might have exhaust vents above the propeller. The reason I think this is because when I'm idling with the motor trimmed up, the rumbling engine noise is higher and then when I trim it all the way down, the engine noise gets muffled because the exhaust vent get submerged. Is my thinking correct? And if I am correct, does this mean I should NOT modify my prop with vent holes??<br /><br />Thanks for any help!

 

[walleyehed]

Re: drilling vent holes in SS prop

Exhaust is vented thru several openings in the lower unit...by trimming up at idle, you are exposing some of these openings.<br />Drilling the prop is for better hole-shot performance from the prop, not the engine itself.

 

[BassCat73]

Re: drilling vent holes in SS prop

Thanks Walleye. You'll probably be answering all sorts of questions I have. You answered me before. Only had a boat since last fall, now I'm using the winter months to get educated and make my boat the best it can be. Anyhow, I've been reading a little bit about these ventilation holes. I think I read on one thread from here, that if your exhaust runs above the prop and not through the propeller, then you should not drill vent holes. Can you explain this better? How do I know if the type of exhaust system my engine uses will wok for vent holes?<br /><br />Thanks,

 

[Scaaty]

Re: drilling vent holes in SS prop

Drilling Stainless...best to get a 1/8 Carbide bit..center punch, not to fast, lots of pressure, AND LOTS OF THE BEST CUTTING FLUID. Not oil, but Machinist cutting fluid. After that, high speed steel okay, but buy a 12 pack, as you will probably burn them up. Stainless is tough stuff.