25P mirage plus rpm/efficiency limits???
 

I have a 85 Cigarette mistress with TRS, always ran last 4 years a 25 Mirage plus, many engine issues have never let me really dial it in..just redid engines again and the boat has gained rpm so for but no speed...

hitting 5500rpm@70 mph yesterday with a set of near new out of the box 25 Mirage plus, the other day I saw 72@5600 with my old 25 Mirage plus that were labbed 20 years ago... one has a tiny little ding in it, I figured the new props would have been better...
4 years ago with a set of 565's@600 hp the boat went 73.7@5500 with the "crapy" mirage plus's
So now I am wondering if the additional power is blowing out props up top? 5500@70 mph is 19% slip so Need to see whats going on...

My plan was to spin same 25 plus to 5700-5800, do they just lose efficiency at some point at higher rpm no matter what?? almost seems like it... deep TRS don;lt help anything either...

It looks as thought the Lab recipe is providing a more efficient outcome than the new props. This doesn't really surprise me since it is only a 100 rpm a 2 mph difference.
The props don't tend to lose efficiency unless the boat rises high enough in the water colum due to speed and lift (aerodynamics / lifting strakes) to allow the props to pull surface air.
Or, a cavitation bubble is forming at the higher rpm from the gear case, speedo pitot, transducer etc.

Brett

What is a good next step? Tried 24 hydromotive 4 blades saw 71@5500 1-2ft chop

Drives spinning out, got a set of 26 bravo1 to try, wanna see what a 22bravo1 found if I get rpm up more engine should be good for 5800-6000 top end

Rev4 is supposed to do real good working on locating them also to try

Try everything you can and record the data. That will point you in a direction to achieve your goal.
We have a test prop program too.

Brett

I can't emphasize enough to record good data. NOT just WOT rpm and GPS speed, but RPM vs MPH at 200 or 250 rpm increments from idle to WOT. Then graph that data. It provides a great overall picture of what the prop and hull are doing. You can then overlay data from different props for comparison.