Hard to Plane

[Hozelitis]

Been out of town. A couple questions: is it OK for my 4.3 EFI to be using 1.47 gearing? Would a 4 blade 14x17 prop be correct?
Thanks

[bman440440]

Originally Posted by Hozelitis

Been out of town. A couple questions: is it OK for my 4.3 EFI to be using 1.47 gearing? Would a 4 blade 14x17 prop be correct?
Thanks

it is ok for the 1:47 gearing... but now comes the question of how that drive got there?? that drive is for an 350 v8... so going on the idea that for some reason it got changed you need to verify that it actually is a 1:47 not just what the sticker says on the drive... it could have the v6 lower and a v8 upper(where the ratio sticker is) and who knows what the end ratio is now... so I would suggest that you pull your spark plugs and put it in drive (make sure the prop is locked in gear, mark the blade that is closest to top) and put a mark on your crank pulley and spin it 1 time around and see where the prop is now... it should be just past 1/2 rotation (65% of a rotation to be exact) for a 1:47 ratio... if so then get the 14x17 4 blade prop like the one I suggested

[Hozelitis]

Originally Posted by bman440440

it is ok for the 1:47 gearing... but now comes the question of how that drive got there?? that drive is for an 350 v8... so going on the idea that for some reason it got changed you need to verify that it actually is a 1:47 not just what the sticker says on the drive... it could have the v6 lower and a v8 upper(where the ratio sticker is) and who knows what the end ratio is now... so I would suggest that you pull your spark plugs and put it in drive (make sure the prop is locked in gear, mark the blade that is closest to top) and put a mark on your crank pulley and spin it 1 time around and see where the prop is now... it should be just past 1/2 rotation (65% of a rotation to be exact) for a 1:47 ratio... if so then get the 14x17 4 blade prop like the one I suggested

Thanks much. I’ll let you know.

[Hozelitis]

I finally had smooth enough water and my WOT was 3950 rpm by the boat tach, 48 mph by the boat speedo and 45 mph by a speedo on my phone with the boat trimmed out. The prop is nicked a little on one blade, probably smaller than I thought at 1/4" x 1 1/2".
Should I still find the actual gearing or can we tell what prop I need by the WOT?
Thanks

[mmwjr]

Going from the 21inch pitch to a 17 inch will increase WOT by about 500 rpm and get you in range. Add a blade will help holeshot but the increase in WOT will be less. Your top speed seems good so if it was me I would go with at 4 blade 17 inch pitch.

[Hozelitis]

Originally Posted by mmwjr

Going from the 21inch pitch to a 17 inch will increase WOT by about 500 rpm and get you in range. Add a blade will help holeshot but the increase in WOT will be less. Your top speed seems good so if it was me I would go with at 4 blade 17 inch pitch.

Great. I will take your advise and get that prop. I will post the results.
Thanks so much for your expertise.

[bman440440]

Originally Posted by Hozelitis

Great. I will take your advise and get that prop. I will post the results.
Thanks so much for your expertise.

also after you get the new prop on make sure you are prepared for the hole shot you will have... it might surprise you the first time so be ready... people are amazed at the hole shot I have with 3 LARGE guys, 32 gal bait tank, and a full load of fuel.

[Hozelitis]

Originally Posted by bman440440

also after you get the new prop on make sure you are prepared for the hole shot you will have... it might surprise you the first time so be ready... people are amazed at the hole shot I have with 3 LARGE guys, 32 gal bait tank, and a full load of fuel.

Thank You Sir!

[Hozelitis]

Happy Thanksgiving.
From what I read each 1” in pitch changes rpm close to 200. If that is correct, and I’m at 3950, and go from 21 to 17 pitch, that will put me at the high range of WOT rpm. I also wonder what a quarter inch in diameter and a 4th blade play into it.
Sorry, I have a boating friend that suggests strongly going to 19 pitch.
It is a 17 year old engine and I don’t want to over rev.
Thanks

[mmwjr]

Yes that’s the estimated change in rpm per change in pitch however it differs depending on other factors of prop design such as rake, blade area, ...

Adding a blade will decrease WOT which is why I suggested a 17 inch pitch going to a 4 blade that it think you will like over a 19 inch 3 blade. Your boat your call.