[stereoman405]

Just took my 21' Talari cuddy out for a spin after installing a Performer intake and Holley 650 carb on a fresh Vortec 5.7. (Replaced the OEM 2bbl setup).

Boat also has Captain's Choice, and a 1.47 ratio. After tweaking the timing I hit 51.5 MPH GPS @ 4375 RPMS spinning a 14 3/4" 21p Mirage prop (48-13702-21). 60 Gal of fuel and two passengers on glass.

I thought that this motor should be hitting 4800 - 5000 RPMs. Should I re prop to get the extra RPMs out of her, or should I assume that the less fuel I would normally carry be a little closer to the mark?

Also at WOT she trims out nice, but at mid speeds I get some porpoising. My calculations put her at 13% slip, so I don't really want to go smaller diameter the get the RPMs.

Do you think a 19p would just get the RPMs up without much top end increase? At least it might feel a little more punchy. I'm starting to have secind thoughts selling my BB Chapparral...

[mikeyt]

hmmm....good question. I would be tempted to try a 19" pitch Mirage since you have sufficient room (@ 4375rpm WOT) to not exceed the maximum rpms (it wont hurt to reach 4900 at WOT) with the change. I dont 'think' it will give you any more top speed ( it might though cuz of the additional rpms) but you shouldn't lose anything and you should gain a little more low end grunt & mid range oomph. I'm thinkin' the 19" might be the ideal prop for your boat. It wont hurt to have a spare prop anyway.....

btw....if you have a choice i would go for the Mirage 'Plus' version. The Mirage Plus is cupped more and will likely have the flo torq hub system, meaning the prop can fit many engines with the correct hub kit. Here's a link to one presently on E-bay: Click here

[stereoman405]

Thanks Mikey. I just got off the phone with a local prop shop and he thinks that my problem is that I'm running too big of a diameter prop, something more suited for a big block. He recommends stepping down to a 14.25" diameter and then upping the pitch to 22P. He said that the reduction in diameter should allow it to spin more freely, then the 22P will help add a little up top.

I have a spare generic 14.25" x 21P sitting at home I think. I'll start there. That way if I over rev it I know I can pull the 22... Unless there are other major factors that a good 22P Mirage Plus would have that would benefit me?

[indykoch]

I think the smaller diameter will definitely help your situation, but I'm doubting you'll be able to go with a 22P. I think the 14.25" X 21P will be darn near perfect if Mirage Plus and/or SS.

Just for comparison, I have a 14.25" X 21P SS on my 300 hp 350 Mag and I can't quite get 4700-4800 RPM's. I believe my boat is a little less weight as well.

Keep us posted on your results!!

[blockp]

If you have the 21p, definitely try it before buying the 22. My 202 with 5.0 can't push the 14x23p aluminum fast enough. I top out at 4400 & 48 mph. With a 14x21p aluminum, I top out at 4800-4850 & just a teansy bit shy of 50 mph with the boat empty.

I just bought a stainless torque shift prop and am waiting anxiously for it to come in. A buddy had one of these 15 years ago or so and it was phenomenal. I'm hoping I don't have to rebuild too much of the inside of it to make it shift properly. Can't wait though... 14p hole shot & an adjustable upper end of up to 26p run out. I imagine I'll be setting the upper between 21 & 22p, but I'm pretty pumped waiting for it to come in though

[mikeyt]

I would be surprised if the 22" gives you what you are looking for. Something to keep in mind is that a Mirage 'Plus' prop runs about 200rpms lower than a similar size original Mirage prop does due to the difference in cupping. So increasing to a 22" would likely keep you at the low (or even below) your recommended rpm range. The other issue would be the likely slight loss of low end/mid range 'grunt' with a 22. The Mirage Plus is also reportedly slightly faster though than the original version in most applications. I agree that you should try the other 21" prop you have just to see what happens.

I wish it was a simple job though to pick the perfect prop for every boat. Unfortunately it can be a bit of trial and error in many situations as similar boats can run the same props and yet get different results due to other influences. Also, you could speak to 10 prop 'gurus' and likely get 4 - 6 different opinions. At best, it is sometimes no more than an educated guess at what will work best....

[stereoman405]

Originally Posted by indykoch

Just for comparison, I have a 14.25" X 21P SS on my 300 hp 350 Mag and I can't quite get 4700-4800 RPM's. I believe my boat is a little less weight as well.

Keep us posted on your results!!

What kind of top speed are you seeing? (GPS'd if possible.)

Originally Posted by blockp

I just bought a stainless torque shift prop and am waiting anxiously for it to come in. A buddy had one of these 15 years ago or so and it was phenomenal. I'm hoping I don't have to rebuild too much of the inside of it to make it shift properly. Can't wait though... 14p hole shot & an adjustable upper end of up to 26p run out. I imagine I'll be setting the upper between 21 & 22p, but I'm pretty pumped waiting for it to come in though

Lucky dog. Where did you get your hands on that? I had a buddy with a 23' Mirage that ran one of those 10+ years ago, and I was under the impression that they didn't make them anymore?? I'm really curious to see what you're result will be.

I have a local guy selling a 13 x 21P Quicksilver for $125 and I'm wondering if I should snatch that up to throw into the mix. Or do you think that's a little too small?

[stereoman405]

Originally Posted by mikeyt

I would be surprised if the 22" gives you what you are looking for. Something to keep in mind is that a Mirage 'Plus' prop runs about 200rpms lower than a similar size original Mirage prop does due to the difference in cupping. So increasing to a 22" would likely keep you at the low (or even below) your recommended rpm range. The other issue would be the likely slight loss of low end/mid range 'grunt' with a 22. The Mirage Plus is also reportedly slightly faster though than the original version in most applications. I agree that you should try the other 21" prop you have just to see what happens.

I wish it was a simple job though to pick the perfect prop for every boat. Unfortunately it can be a bit of trial and error in many situations as similar boats can run the same props and yet get different results due to other influences. Also, you could speak to 10 prop 'gurus' and likely get 4 - 6 different opinions. At best, it is sometimes no more than an educated guess at what will work best....

Hmmm, I'm also getting a little mid range porpoising, I was thinking it was due to the cup / diameter of my current prop. Sounds like the 'Plus' might compound the problem.

What sucks is that I don't have much time to test this our before the boat get's moored this weekend, and the water is too damn cold for prop swapping. I guess I'll just have to suck it up and expect not to get it perfect for a bit.

[mikeyt]

A set of trim tabs, whether they are Smart Tabs or Lencos or whatever, would likely reduce/resolve any porpoising issue you might have. Your boat size is likely close to the upper limit for Smart tabs to be effective though. Hopefully someone here with a 21-22' boat that has Smart tabs can weigh in on that....

[blockp]

Originally Posted by stereoman405

Lucky dog. Where did you get your hands on that? I had a buddy with a 23' Mirage that ran one of those 10+ years ago, and I was under the impression that they didn't make them anymore?? I'm really curious to see what you're result will be.

I found it on a local CraigsList, simply advertised as a "stainless steel mercruiser prop". There are a handful that show up, but most of them seem to be in the $300-600 range.

You're right, they did quit making them a while ago, but apparently this guy bought up remaining inventory and patents, because he is selling the internal parts to them and manufacturing cam lobes for them too.