mirage diffuser / rev 4 diffuser
 

496 mag ho turns a 25 mirage plus into the soft limiter every time, no problem and on plane acceleration is kind of a wow factor, for me anyway.
there was a fair amount of chine walk at wot actually it would start in the high 60's all thru best ever speed of 73. ?
"theres a pic of that best ever somewhere"

friend says start cutting the diffuser ring off an 1/8 inch at a time and see if it helps, it did and i have it cut down prob 3/8 of an inch now.
chinewalk is all but gone so i can let it run wot but theres that limiter issue again,
plus it can now in some instances blow out at lower speeds

bought a new 25 rev 4, it cured the chinewalk, on plane acceleration isnt quite as hard and so far best speed is 72.6 @ 5130 rpm.
So its right there at the limiter again.

the rev 4 is box stock and the mirage plus was never repaired but sent to fj to verify and it is also stock.

i know less than nothing but it was reasoned to me :
that the flaired diffuser on the mirage lifts the stern and contributes to the chinewalk &
that the long straight diffuser on the rev 4 aids in stability ( maybe something about the aspect ratio)

i have no idea if stability was gained going from 3 to 4 blades or if was the long straight diffuser on the rev 4 ??

before i send the pcm off to get the limiter bumped up a hundred why dont i get a 27 mirage and try it ,,
most likely the ring will need cut down to stop the chinewalk,
so the question is how about having a longer straight diffuser ring added to the mirage ?

Before you start changing rev limiters and cutting more diffuser rings I'd do more testing.

I'm surprised you pulled to the rev limiter with the Rev 4 25" prop. It has significantly more blade area than the Mirage. Typically with equal pitch Mirage and Rev 4 props the Rev 4 would load the motor more. It has been my experience to drop 2" of pitch when going from a Mirage to a Rev 4. For example Mirage 25 I'd goto a Rev 4 in 23" as a starter.

The longer barrel on the Rev 4 will typically make the drive more responsive to trim and steering, that coupled with the massive blades will hold the nose with less trim. And yes the lack of diffuser will have less stern lift.

IF it were me, I'd try a Mirage+ 27 without mods first. Then perhaps tweak the Rev 4 just a tad to bring the rpms down a tad.

What kind of boat?? I would try a stock 27 Mirage + and the have it labbed and diffuser cut down. BBlades has a winter special on labbing

Just my opinion but I think it will be a dog with a 27.

Chris

boat is a 26 x 8 no cabin retired raceboat that i did a rebuild on.

all tests have been calm water, similar to conditions in pic.

the 25 mirage plus would spin into the soft limiter,
chinewalk after the ring was cut down wasnt bad but the combination had me pulling back to keep
it @ 5140-5150 rpm,
not knowing what the mirage could spin up to is why i went 25 rev 4 and it ended up right at the limiter.
tach is a mercmonitor, speed is gps, fuel is 65 gallons so add that to the weight slip.

i will test a 27 before cutting the ring, and i wouldnt be surprised by any results a 27 netted me.

just dont know where the stability came from, the 4th blade or the long straight diffuser

https://cimg5.ibsrv.net/gimg/www.off...2035c68a56.jpg
https://cimg2.ibsrv.net/gimg/www.off...cb4a55db6b.jpg

If enough of the diffuser is cut off, you may not be able to plane the boat, it will slip ao bad. . Happens with some.

Happened to me with a few of the props I have ended up with.

Ended up blocking the exhaust passage in the outdrive and wallah, perfect grip ! Never would have imagined. I used a rubber PVC cap, but that was not a Bravo.

Tinkerer fixed his diffuser cut off slip induced issues also by blocking his on his Bravos. Forget exactly how he did it. Do a search with his name.

Got a 27 mirage plus to try, it appears box stock in really good shape.
i cleaned it up with a purple scotchbrite and see no tool marks or stampings.
its tracking almost perfectly and balanced on the money so it can go right on and get tested.

heres the thing, should i try it as is or should i straighten the diffuser ring first ?
testing on saturday so i got all day tomorrow

https://cimg0.ibsrv.net/gimg/www.off...d920384776.jpg

Do not cut the ring. Try the prop as is. Then make adjustments, if needed.

Tested the 27 mirage plus today best ever speed 74.3 best rpm was 4900 (i will have to check that)
it jumps right up on plane and liked alot of trim.

have to watch video seems like it might have pulled 4900ish becacause i remember thinking it needs another 150 rpm.

chinewalk was almost nil, seemed like tab would induce it and more trim it would stop.

i have alot of video to go thru and digest.

the river was calm, glass on last run, ocean was 1& 1/2 feet @ 9 seconds winds under 12 mph

it ran completely different from the 25 mirage plus.

let me get it sorted out but im looking for direction/suggestions

thanks

https://cimg4.ibsrv.net/gimg/www.off...4fedd11962.jpg

https://cimg7.ibsrv.net/gimg/www.off...852ad0caf5.jpg

https://cimg5.ibsrv.net/gimg/www.off...6e65957346.jpg

I would now cut the barrel and have that 150rpm more if lucky. When i cut the barrel of my mirage plus, there was no difference in planning. My propshaft is 5" deep. You can weld the diffuser back if needed.

https://cimg0.ibsrv.net/gimg/www.off...115c476851.jpg
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Third piece of tape from front is the end of inner strake, from that piece all others are on 24" centerlines.
video to follow

seems like it runs hi and flat, looks like the inner strakes are just barely getting some water
and it looks like the hull is dry outboard of the outer strakes, to me thats why tab causes chinewalk
(some port tab for torque roll) like it crabwalks and starts the wiggle.
probably way off here but i think move the tabes inboard and set them flat.
i also think the 150-200 rpm the 27 m plus needs will come from sanding the bottom,
it's too easy to send the prop in when there is some little tweaking to do.
besides i'm flush with time and dumb ideas.
any opinions from the guys who really know set up i would greatly appreciate any and all

Sand the bottom with 300 wet and that's it. Lop ⅛ to ¼ off that diffuser and try it again Next step would be going a little less diameter on the prop but keeping the same cup at the end of the blades. Fj for that

The hull is running quite clean. I like the attitude. You slip % is 11. This is quite good.
I believe a diff. mod and the correct Lab recipe will get you to the end goal.
If you can maintain the 11% slip and reach the max rpm with the 27, there wont be anything left on the table. Don't remove diameter from the 27 M+

Brett

Ran another test.
first video shows the camera wasnt mounted square, have to work on that
second video was at 40 mph, trim nuetral. 27 p mirage plus
the battery died before the wot runs.
its interesting to see what goes on back there and hopefully next week ill get some video at wot, looking for any opinion ( anything look right or wrong)

Cool videos Dan. I did similar on mine. Was going to try mounting the camera on a trim tab pointed at the prop to see if that view was any clearer. Might be worth a shot.

Last video was drain plug cam, it has to be turned on before it goes in the water, the remote doesnt work unless its close to it and then you cant see if its recording or not.
I will get clean wot video of the drive one way or another, i believe its gonna point me or more likely someone who really knows setup in the right direction. (already got advice and that will get tested in the next few weeks)

a cushion clamp frankenstein thing may be in order to get the camera out on the tab or its cylinder

https://cimg2.ibsrv.net/gimg/www.off...efb844c53a.jpg

The go pro adhesive mounts are cheap on amazonalamadingdong. I stuck one in the notch on my Baja right above the drain plug and she held on. Matter of fact it’s still on there.


https://cimg7.ibsrv.net/gimg/www.off...1a3892db2.jpeg

thats a pretty clear pik where is the rest of the video??

The best part of the videos is while idling and watching the bottom of the lake. While running it’s just a chaotic mess. Camera too close the the water, hard to get a clear sight of anything. That’s why I wanted to mount it on the tab to get it away from all the wash.