Enough RPM for bigger pitch?
#1
Enough RPM for bigger pitch?
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!
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!
#3
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Join Date: Jun 2007
Location: Denham Springs La.
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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!
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!
#4
Chris
Gold Member
#7
Chris
Gold Member
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
Chris
#8
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.
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.
#10
Charter Member # 55
Charter Member
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.