What RPM's should I be turning?

[1996Z15]

Well I finally got to take the Minx out for it's maiden voyage and am I ever glad I bought it. Unfortunately the speedometer doesn't work, I guess that they aren't all that accurate anyway, but the tach read 4200 RPM's. The boat has a Mercruiser 350 Magnum with an Alpha 1 drive that's turning a 23" cleaver prop. NOTE: I am no boat or propeller expert so I can't answer any technical questions. My questions is twofold; approximately how fast do you think that the baot was going? What type of RPM's should this boat be turning?

Oh yeah, on the trim level gauge where is typically the best setting for this boat? I have been trimming it up to, what would be the 1/4 level from the bottom (if that makes any sense to anybody).

I'm not looking to set the world on fire but I would like the boat to run a respectable speed for what it is.

[BUIZILLA]

My Minx LE turns 4200-4300 with a 23 Mirage, and 4400-4500 with a 21 Mirage.
You NEED a 21 Mirage.
MAX rpm in the book for the Magnum is 4800 however..
Mine runs 56.6 on GPS with the 21, and a 350 Magnum package.
This was trimmed out till ventilation, and just back in, to hook up and load the motor.
Stability and attitude was excellent with either prop.
I would like to try a 20 Turbo just for grins.

J

[tmdog]

Z15, Need to know your outdrive gear ratio. Assuming it is a 1:1.50 ratio you would probably be going between 50-54mph. A simple method to calculate optimum speed is as follows. Remember this is optimum speed with 0 slippage. All props have slippage from 5 to 15%, so you have to deduct.
Rpm divided by gear ratio x prop pitch divided by 12 divided by 5280 x 60 = optimum speed. Your trim sounds about right. Was that your top rpm? Jim

[1996Z15]

Yes, that was as fast as I could get the boat to rev. How fast can you comfortably make these boats without breaking the bank and getting squirrely?

[BRIAN73]

Z15,

My good friend has a 1988 Minx with the same combo. In its stock form it turned a 23 Stilleto 4300 RPMS.

Over the winter we put bigger heads, intake,pushrods, roller rockers and a Holley double pumper.

Total cost for upgrades,$1,200
The boat really get's out of it's own way now.

With the same Stilleto, he was now up to 4900.
We are going to try a 21p cleaver this weekend.

Don't forget to spend the money for a good drive shower, It's cheap insurance!!!!!!!!

Brian