On my 21, I'm currently spinning a 27 Mirage plus and will be getting an older style 29Mirage to try. From everything I've read, the 29 acts like a 31? So I fugure I should drop around 200, maybe 300 rpms going from the 27+ to a regular 29... which would be good, cuz I wouldn't mind loosing some revs.

this is my thinking- I'm adding 200rpm for the older style mirage (less cup), and taking off 400 if it runs like an 31= 200rpm drop expected.. sound about right? I've never run a 29, but I hear its completely different than the other mirages... would really like to see how it works for me.

You also have 15" diameter so the rpm drop will be more in the 300-400 range.

Brett

It takes alot of power to spin a 29 plus ... A standard 29 mirage is still a lot of prop for most engines to turn.
I started with a stock set of 29 plus props ... could only spin them 5200 rpm @ 89 - 90 mph .Engines made max power @ 5700 so that was my goal. Had them labbed and couldn't get the boat on plane . Sent them back for adjustment ... was able to get on plane after many attempts with my buddy in the bow ... boat ran 91 - 92 mph @5600 . Send them back for some more adjustment ... very difficult to get on plane and speed was 86 @ 5800 . 29 plus props didn't work for me ... Because the diameter is 15 inches on the 29 compaired to the 27's 14 5/8 inch . 27's way to small ...29 to much in stock form. Forget about the standard 400 rpm difference between pitch sizes.

I would run your stock 27 and save your money.

I really wouldn't mind loosing 300rpms. Spinning 5800+ during the mid summer heat, so I figure its probably worth a try.

I appreciate the input guys.

I have a labbed 27 mirage ( not plus ) $ 250.00 plus ride

If you have the prop to try, do it. That'll give you better info than anyone of us ever can. If it works and you like it, buy it, if not, don't.

This past summer I tried a pair of 29 pitch Mirage props back to back against a pair of 27 pitch mirage plus props.The 29's were 600 rpm lower than the 27's. 4000 rpm for the 29's compared to 4600 for the 27's. What surprised me was that the boat ran 65 mph on GPS with both props.The slip with the 29 was 10 % and the slip with the 27 was 17%.Boat was a Formula 311 and was difficult to get on plane with the either prop. One 29 prop was a Plus and the other one was a std 29 but the rpm was same for both at 4000.

I figured the 29+ would be a little lower on a twin application.

Impressive the speed #s were the same.

I've got a heavily labbed 29 Mirage Plus that I'd be willing to let you try. It was worked by Houston Propeller for a 25 Baja project we built, great top end, big cavitation coming on plane. I've also tried it on a friends blown 18 Donzi, worked real well on the light boat.

Very nice Superboat btw, been checking out the pics on BF and Donzi.net Would love to own it!

Kurt

Yeah, I've seen the posts over on BF.. its a great boat. Really kills me to sell it (and I've actually be working on being able to pull it from the market- so far its still for sale, tho).

In the spring I plan on trying my solid hub old style mirage and seeing where that puts me, then go from there (might take you up on the offer). I'd really like to borrow a -2 sporty lower, or buy a -3 imco and try it.. Kunkels has a -2" sporty I might be able to borrow. I think it'd pick up speed since the prop is buried pretty deep.

Kurt, if you ever get over this way, let me know and you can check it out.

Nick