new nitro prop

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yoggii

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I just got a 1991 17 ft nitro.rated for 120 hp.It has a 115 evenrude with a 13 x 19 aluminum prop.prop is beat up so im gona put a stainless prop on it.Any suggestions on a new prop??? pitch? 3 or 4 blade? Does anyone know the max rpm for this motor?the cover says high performance on it..thanks!!
 
jestor68

jestor68

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Re: new nitro prop

Rpm range is 4500-5500. To choose a prop you need to know what rpm it's turning now with the 19 pitch, in order to decide what pitch SS prop to get.

Is this a Nitro bass boat?
 
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yoggii

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Re: new nitro prop

19 3 blade alluminum turning 5300 rpm,poor hole shot with just me,im thinking 4 blade ss 18 pitch,any thoughts??
 
jestor68

jestor68

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Re: new nitro prop

What are wanting to accomplish in terms of performance? Good hole shot versus top speed are different goals.

Generally speaking a 4 blade will provide better hole shot, but less top speed.

A 18 pitch BRP Raker 3 blade would give decent hole shot and nice top speed A 4 blade Solas HR Titan 17 will give better hole shot, but a little less top speed.

Running a SS prop should allow you to raise the motor at least one hole for better overall performance.
 
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yoggii

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Re: new nitro prop

ok,I got tac fixed and motor running great,,5600 rpms trimed up and streched out with aluminum 19 pitch 3 blade prop.Im thinking a 21 pitch ss 3 blade will drop rpms about 300 and get me to about 5300 since 5600 is a little to much.Maybe a little more speed(48 mph now) and hopefully hole shot will be ok. any thoughts??anyone??
 
jestor68

jestor68

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Re: new nitro prop

Your estimates are a little off. A SS 21" will drop 400-600 rpm compared to your aluminum 19" and pretty much kill hole shot, which you say is already poor. When switching from AL to SS the amount of rpm change per inch of pitch is different.

The ideal WOT rpm for your motor is 5500; the range being 4500-5500. So, going to a 19" SS will drop about 150-200 rpm. To maintain 5600 rpm, you'll need a 18" pitch in SS and have a better hole shot with maybe a slight speed gain.

Bottom line; a 21" may be too much, depending upon what sort of over all performance you're after.
 
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yoggii

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Re: new nitro prop

So you are saying a ss prop of same pitch will turn fewer rpms than alluminum prop. I read on iboats that a ss prop turns more rpms because blades are thinner.
 
jestor68

jestor68

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Re: new nitro prop

yoggii said:
So you are saying a ss prop of same pitch will turn fewer rpms than alluminum prop. I read on iboats that a ss prop turns more rpms because blades are thinner.
Click to expand...

The thinner blades with more cupping will be more efficient in grabbing and pushing more water, which actually causes the motor to do more work, which results in a slight lose of rpm while increasing speed. This is the case if no change is made in the set up. But you can usually raise the motor a hole to gain back the rpm and get even more speed increase due to less gear case in the water.
 
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yoggii

Seaman
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Messages
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Re: new nitro prop

Makes sence to me,I have one more question,I see people on here talking about their 90 and even 75 hp engines turning 5800 with a 22 pitch prop and I can only get 5600 with a 115 with a 19 pitch,what is it gear ratio or are they exagerating a little??
 
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