two more ideas:
1) I would check your timing advance too. just to make sure that you are getting full power out of your BB at WOT.


2) ask on the scarab forum for typical speeds for your boat. see if you are unique or in the norm. and ask for setups from others. I did that for my 272 on the formula board and found i was right with or better than others. so im keeping my prop selection and labbing them.

seems liek i am runnign sloer than similar hull. Mine is unique due to the alpha. I am leaning more and more to a bravo conversion. I prety much just want tos ell eth baot and get a faster hull to srart wity. I think she might be easier to sell with a bravo and a BBC than an alpha.

Puder first off I am going through the same problem with my formula. Top speed 60mph on a very good day. Gear ratio 1.5-1. Prop 27 pitch 13.25" diameter. MPH at WOT is 4600. My numbers are up there as well. I am going to play with props this year if I can get the damn thing running right!! :D:D

Prop slp on Scarab w/Alpha
 

Puder, it seems to me you are running "close to the edge" with that size boat and an Alpha drive. I'm not sure I would want much better bite with the Alpha.

There are obviously many ways to improve your slip/prop bite, but they will all tax the Alpha.
The Bravo will handle lots more power but will probably slow you down with equal power.

I say check all your measurents with shop gauges and GPS and dial in the prop just a bit and run with it.

Your speed is not too far off for that size boat and power.

Good luck.

what do you want me to measure with a shop gauge?

Prop slip
 

Puder, what I was talking about was using a tach from your marine mechanic that clipped on to verify your rpm. That would be a starting point of reference.
Also, the GPS would verify speedo readings.

Typically, larger diameter would give you better bite and less slip. Then adjust pitch to get in correct WOT rpm range. However, better bite/less slip will place more load on the drive.

Can your Alpha reliably handle any more load ? Do you use a drive shower and change outdrive lube regularly at short intervals ?
Good luck,

update on this problem. I have been puffin the crack pipe. I run a 19p mirage+ not a 21.


Its been a long winter......