1988 28 Scarab Excel Prop selection confusion
 

Hi all,

My '88 Scarab was originally equipped with a 454 MAG, Bravo1.
The original Engine wiped the cam at 450 hrs and was replaced with a 330 HP with small port heads.

I felt I would need to change the Prop to adapt to the milder Engine. I started researching, and got really strange results...
I used the Mercury Prop Selector based on the known Prop that's on now.
While I can't pinpoint what, I think something IS wrong here.
Current Prop: Mirage (not plus!) 15,25 x 19P
Current Top Speed 40 MPH (GPS) @ 4300 RPM
Prop Selector recommends a m+ with18 or 19pitch or a Rev4 with 17 pitch calculates Speed to be 51MPH.
Then I read a post on the forum saying that 454 MAG B1 Scarabs came with 23 Pitch Mirage Props...??!

Now I wonder if the previous owner changed the Prop to 19 pitch and what would happen if I put on a 23 pitch Prop.
Also I feel that the Boat is too slow at 40 MPH. Using above data with a slip calculator, slip is way to high.
Can the rubber hub of the old Mirage Prop be slipping?
Which Prop is a good starting point?

Any thougts / input greatly appreciated

With the 454 mag (365 hp), boat should run 58ish with a 23p mirage. Loosing 30 hp shouldn't be a big issue. You should still be running 50+ with a 23p.