Wanting more speed

[Jagged Edge]

I have a '03 Donzi Classic 18'. It's a 350 mag, 300hp with a Alpha drive, I think a 1.5 ratio. The prop is a 14.5" 25P Mirage Plus. It's turning about 4200 rpm's at a gps speed of 57 mph with the trim up to the first line on the gauge from the bottom.
Do you think a 23P Mirage Plus would give me more top end and still give me good cruise speed?
Thanks
Ron

[Rootsy]

at 25P with a 1.5 ratio you are overpropped and pulling the engine too far down, 4200 is definitely too low for that motor... the boat should be propped to run in the specified WOT range given my mercury for that engine which is i believe 4400 - 4800 rpm... or real close to that range? also verify you are getting WOT at the throttle body when the throttle is all the way down on the control.

i'd drop to a 23P and the amount of torque that it takes to spin the 23 vs the 25 at the same rpm may in fact allow you to pick up 400 - 500 rpm...

too bad mr oak is on his honeymoon cause he could elaborate on your setup better... he has an 18 - 350 mpi (300 pshp) and a 1.65 ratio bravo and spins a 25 mirage (labbed) 5000+...

but there are plenty of folks that have the same setup who will elaborate for ya...

going from a 1.47 (gen II ratio) to the 1.65 equates roughly to about a 2 inch prop change generally.

i find that the best way when playing with props in order to find optimal trim is to watch my gps which i have mounted on my grab rail slightly left of the steering wheel... when you obtain optimal trim you will be at max speed and when you overtrim you will feel the change in motor tone as well as maybe pick up a bit of vibration but more than that the speed will begin to fall off due to increased prop slippage because the angle of attack becomes too great.

[BUIZILLA]

Jag, asking for opinions on prop's, is like asking about oil around here eek! :D

My opinion, a 22 Turbo 1 or a 23 Mirage, not a + would be better, the plus tends to bounce the nose around a little. Your way overwheeled aith the 25. I have a 23 Mirage on my 18 and it likes it.

J

don't shoot me....

[Jabes]

There is a 23a Turbo 1 prop for sale in the "parts for sale" classified. Might work well.