New prop advice

[Gary H NC]

I got a 4.3 cobra with a omc raker style 3 blade
I believe the prop is 14.5X20.
My WOT is 4400,about where it needs to be.

My old prop is looking pretty nicked up and looks like it has been fixed a few times.

I'm not looking for big gains in speed,just want a good replacement.Would a 4 blade the same size and pitch do a good job?

 

[Tail_Gunner]

Re: New prop advice

I've played around with a few 3bl and a few 4bl, i really liked the smoothness a 4 bl gave along with greatly improving the ride, It actaully lifted the boat farther out of the water, far enough that the wake shot directly out the back of the boat, absolutley none on the side's.

The boat i have is a 4.3 about 2800 lbs dry efi though with a 1.66 gear ratio, i could turn a 19p bl al to 5000 with no problem, a 20p 4bl ss to 5900 And gain 5mph.. 54mph, 22p 4bl ss only hit 4500 but 43.4 mph a tad to slow for that 4.3 rpm that is

Stilletto was the prop brand and while not as fast as a 3bl it's a much smoother ride and really quite a bit of difference in vibration, engine drive combo. Id bet a 18 would be in the right zone, let old marble eye's respond.

Is that the max rpm that motor is setup for? that's 400 underneath mine... and for what it's worth iv'e read quite a bit lately that seem's to indicate a carbed motor produces more tourqe than a efi type.

 

[walleyehed]

Re: New prop advice

That Raker is a bit different than most 3-blds and has alot of lift. If we go 4-bld on that rig, you'll see a noticable amount of stern-lift. For a Bay pro 4-bld stiletto, we run into another problem because both props are even number pitch. The Bay pro II you drop 1" from a 3-blade for simular RPM.
Yes, there are some pretty 4-bld props out there, but unless you can change the drive height, you can't use the technology built into one and 99% of the time, a quality 3-bld will give best performance.
What speeds are you capable of with the Raker?
How is the hole-shot?

 

[Gary H NC]

Re: New prop advice

Thanks for the replies, I'm hitting about 40 to 42 mph at 4400 rpm. Per speedo,no gps..
I know my engine is rated for 4600-4800 rpm.

Hole shot is not bad with the old prop,smart tabs installed to get me up on plane..

A few more mph would be nice but not a big deal..

What brand and style 3 blade would be best?

Old prop has a number 394753 stamped on it?

 

[walleyehed]

Re: New prop advice

A Stiletto in a 19P should be a good choice, maybe a bit better hole-shot, and it'll get the RPM up a bit closer to where it should be...
iboats has'em....1-800-718-1233, P/N for your app. is 20319.

 

[Gary H NC]

Re: New prop advice

Thanks Walleye,
Will dropping to a 19 decrease the top speed by much?
I looked back in my Omc manual and my engine with 2bbl carb is 4600 max.

 

[Gary H NC]

Re: New prop advice

Also noticed that stiletto was 14.25,will changing diameter affect anything?

 

[Crownie2]

Re: New prop advice

The top speed will probably go up a little and don't worry about the diameter... Should be a win-win for you.

Bob

 

[walleyehed]

Re: New prop advice

In my testing of both the Raker and Stiletto, a 21P Stiletto is closer, number-wise than a 19P...to a 20P Raker.
That Raker is a Good prop but usually best suited to surfacing conditions, so you're not really being able to use the full technology of the prop, although you may be getting some good lift with it..
All things considered, I think the 19 Stiletto will be much closer RPM-wise, and should give better results over-all.
The speed may be about the same though, atleast don't expect a huge increase...you're already below your max RPM so I don't think you want to go any higher in pitch.
Higher pitch doesn't always mean higher speed.

 

[Gary H NC]

Re: New prop advice

Thanks Walleye,I will give it a try.
Sounds like a good christmas present to me!8)