what gear ratio would it be if my motor turns one full turn and the prop turns 2/3 full turn. i cant get my boat to stop over reving. i got a 28 scarab excell with a 454 and i cant go past half throttle. please help me. i got a 23p mirage 3 blade now and i cant imagine i need a bigger prop than that on a stock motor. cant go much past half t hrottle and im already at 4600

if you have a 1.5 ratio, your engine will turn 1.5 times for 1 turn on the prop. so obviously you don't have a 1.5 wich I think is what you should have. Since I'm not a pro at prop, cant tell you exactly your ratio, but turn your engine 1 turn and check your prop. the only thing I can think of is your drive is higher than 1.5, like...1.65 or 1.8...can't remember the other ones. let us know!

Ex. Engine running 5000 RPM with a 1.5 drive the prop shaft RPM is 3333.

Engine running 1 RPM with a 1.5 drive the prop shaft RPM is 0.66667 or 2/3.
So your gear ratio is 1.5:1

Sorry then... I'm lucky I wrote: Since I'm not a pro at prop !

Hydolift, why would he be overreving then ?

I am not a pro at prop either, just read this http://go-fast.com/sterndrive_gear_ratios.htm

I would check the tac to verify that its correct. Then I would find out if the prop is spinning.

At wide open throttle, spinning a 23 mirage, the boat should go about 59 MPH at 4900 rpm. At 4600 rpm, you're way past half throttle.

Sounds to me like a potentially spun prop hub.

the prop is definately spinning the rpms are right. i am just trying to figure out what gear ration i have in this drive

xpx747,

It woiuld appear that you indeed have a 1.5:1 final drive ratio based on the above.

It appears that your prop hub may be faulty and spinning inside of the propeller casting (it's not supposed to) under load. That means that your engine RPM will be much higher than what your prop is actually turning regardless of ratio.

Have your prop hub checked by a reputable shop.