awsomethunder

can a 25 pitch mirage plus be "tweaked" to 24.i need 400 more rpms from this prop and wanted to lab and down pitch.can this be done?

throttleup

The RPM increae is not a problem but there are many ways that that can be done including down-pitching. Post a little data and we'll take a look for you.

Julie

awsomethunder

25ft active thunder,454 mag 365 hp,bravo 1 1.36 ratio.turning 23 mirage 5100 rpm at 67-68 mph.was thinking of switching to a 22 b1 also.i have this 25 mirage but can't pull the rpm

Pat McPherson

I bet if you change to a 1.5 gear you could spin that 25p and see 70mph.

awsomethunder

is the gear ratio in the upper or lower housing?someone else said to change to a 1.50 said the top mph won't change but i will get there quicker

1BIGJIM

Upper

Pat McPherson

From what I have read a 1.5 ratio is better than 1.36 for most applications. The only reason to go to 1.36 is if you run out of prop pitch; like on a boat that goes more than 100mph.
A 1.5 ratio multiplies the engine torque higher than a 1.36.
Your boat will get on plan faster and will likely reach a higher top speed with a 1.5 ratio drive.

B BOATER

Are you sure on that? I believe its lower

throttleup

It depends on the gear ratio.

To go from a 1.5 to a 1.36 the change is in the lower. To go from a 1.5 to a 1.65 the change is in the upper.

There are many various gear ratios that can be combined through the combination of upper and lower gears.

bbladesprops

The 1.5:1 ratio would be the more popular with your particular rig. The low end grunt and throttle response would improve with the 1.5. Top end, with this HP range and pitch and speed window, I would say 6 of one and a 1/2 dozen the other.

That being said, let's work with what you have. Reworking the 25 Mirage Plus can be done to gain 200 rpm without changing pitch, diam. or effecting the efficiency. Your slip is too high to build more into the prop. 400 can also be gained but the speed throughout could be compromised.

I'd try a 23 Revolution 4 for overall performance.

What are the ultimate goals.

Pinion gear change'l do it.