I have twin, stock 5.7L Mercs, Alpha Gen Ones, with 3-blade SS Mirage Plus 19P props. Currently, I'm only getting about 4200 RPM at WOT. I would like more top end, so I'm considering 21P. I know that comes with two tradeoffs:

1) slower out of the hole - which I'm fine with as I never nail it as I feel I have to baby the Alpha Ones based on what I've read on OSO

2) lower RPMs - at 19P, 4200 sound like the bottom range of the spec'd operating range

What can I expect for RPMs if I go to 21P and is that ok?

Thanks!

You will loose aproximately 300 rpm, and the boat will probably be slower on the top end as well.

Chris

Dude that is really low RPM''s for those engines, I would not go up in pitch, if anything I would go with a 17" and see what it does, you need to be turning around 46-4800 RPM good luck...

Ditto

send what you have to someone like Brett at Bblades, he can get you an extra couple hundred rpm and mph from the props you already have.

Double Ditto.

You are not making max HP at 4200rpms. You need to get the rpms higher, not lower.

With a small block engine... many are having great results with the smaller diameter Laser II props. I think the problem here is that the Mirage plus is just too big a diameter for the horsepower you have. I would try a pair of 19 or 21 pitch Laser II's. I think you will find that your boat will come alive with these props spinning around 4800-5200 rpm.

Chris

Thanks everyone - I appreciate the advice. I'm psyched to get more out of it.

Chris - I like the diameter theory. I checked and the Mirage Plus is 15 1/4 dia vs the 14 for the Laser II. I'm going to start looking for a pair of SS 14" 19P Laser IIs. Anyone up for a swap? :-)

Thanks again.

PS - there's something funny about a username with "REDLINE" in it recommending I drop to a 17P prop!

15.25 is a very large diameter for Mirage Plus props, especially for an Alpha drive. You should try something in the 14.5 range. Mirage Plus' do come in smaller diameters as well.