Enough RPM for bigger pitch?

[242LS]

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!

[CB-BLR]

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

Chris

[26 REDLINE]

Originally Posted by 242LS

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!

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...

[CB-BLR]

Originally Posted by 26 REDLINE

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

[HTRDLNCN]

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.

[Griff]

Originally Posted by CB-BLR

Ditto

Double Ditto.

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

[CB-BLR]

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

[242LS]

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.

[242LS]

Originally Posted by 26 REDLINE

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...

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

[Griff]

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.