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JX maximum pitch?
- Thread starter Lighten
- Start date
Pato Sicario
Active member
I guess that depends on what you mean when you say "inefficient"? Push? Speed? Gas?
I have a 5 blade 82. I was looking for max push. I started at 20. Went to 25 thinking it would give better push.
But I found the sweet spot for maximum push on my boat is around 16-17 mark. While the JX is a wide prop, my personal experience is the best push hits at about 1/2-2/3rd's of the max RPM on my boat. It isn't like the older S blades that have a consistent push all the way thru the RPM range. It's a beast for sure. But you have to tinker to find the right set up based on boat, motor and gear ratio.
I have a 5 blade 82. I was looking for max push. I started at 20. Went to 25 thinking it would give better push.
But I found the sweet spot for maximum push on my boat is around 16-17 mark. While the JX is a wide prop, my personal experience is the best push hits at about 1/2-2/3rd's of the max RPM on my boat. It isn't like the older S blades that have a consistent push all the way thru the RPM range. It's a beast for sure. But you have to tinker to find the right set up based on boat, motor and gear ratio.
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I would need to know what ratio gear box you have t chime in here. Mine pushed best at 6000 rpms with a 2.68 gear box. That means the prop speed was 2238 rpm. I believe that prop is designed to redline at 2300 rpm but can't remember for sure. Also mine was 82 inch 3 blade.
What engine rpm do you turn Pato Sicario?
2.67 CH4. Looking for maximum push, really don't care about speed or gas for that matter, it pushes great like it is. Some have said when the pitch becomes to much, your just flopping air around. I have been told its at the edge of its efficient pitch range and that i should try add another blade (dont think anyone makes a extended 5 blade hub?). Adding another blade in a 82-84" diameter would drop back to 20-24 mark maybe? Rather not spin the engine no more than 5100. I like the JX, they take some getting use to for sure, they like to "spool" i guess you could say.
2.67 CH4. Looking for maximum push, really don't care about speed or gas for that matter, it pushes great like it is. Some have said when the pitch becomes to much, your just flopping air around. I have been told its at the edge of its efficient pitch range and that i should try add another blade (dont think anyone makes a extended 5 blade hub?). Adding another blade in a 82-84" diameter would drop back to 20-24 mark maybe? Rather not spin the engine no more than 5100. I like the JX, they take some getting use to for sure, they like to "spool" i guess you could say.
Pato Sicario
Active member
I max out at 5800. It was closer to 54 or 5500 at the 20 mark. I have a 2.55 OxBox. Max RPM on the JX is 2350 according to Sensenich's website. So with your set 2.67 you could be as high as 6200 engine RMP with that prop. or to say it another way, if 5100 is the max you want to spin your engine, you are only spinning that prop at 1900 when its meant to be spun up around 2300. So maybe staying up around the 29 mark is good for your situation. But the next time your're thinking of changing things up, it seems like a 2.3 gear box would be the ideal set up for the max engine rpms of 5100 you want in order to maximize that prop.
This is my second boat and I built it in 2019. Having said that I still feel like a rookie at times. There are others on this site with a wealth of knowledge like Swamp Hunter 45 or Slidin Gator that could maybe offer additional advice.
This is my second boat and I built it in 2019. Having said that I still feel like a rookie at times. There are others on this site with a wealth of knowledge like Swamp Hunter 45 or Slidin Gator that could maybe offer additional advice.
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Slidin Gator
Well-known member
Definitely not an expert here, I have zero experience with that prop or BBC in general. But Sensenich rates the 82” blade at 2350 rpm, which calculates out at about Mach 0.75. Ratio that out at 82/86 and the extended hub would make for a 2,240 RPM limit for the same Mach number. At 5100 engine speed that would mean a 2.3 gear as Pato recommends.
It is my understanding (strictly based on posts by others) that the JX likes tip speed, which contradicts the advice that 1,900 is the efficiency limit.
I would talk to Sensenich, but suspect the answer is less gear vs. more blades unless the true goal is minimum sound signature.
It is my understanding (strictly based on posts by others) that the JX likes tip speed, which contradicts the advice that 1,900 is the efficiency limit.
I would talk to Sensenich, but suspect the answer is less gear vs. more blades unless the true goal is minimum sound signature.
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SWAMPHUNTER45
Well-known member
It looks like you have gotten a lot of great information and tech from the prior postings. I will just reflect back to my earliest experience with the JX in what was a swap test from the legendary “S” aka SuperWide blades.
The JX was like taking your hot rod and putting in a 2,200 stall converter.
As PATO had stated his “best push is 1/2 to 2/3 of his power range”. Some would call this the “snap” while others would call it the peak. The design allows a cavitation or slip down low and suddenly loads and spikes thrust. No doubt a purpose built blade to allow engine platforms the benefit of getting more into their torque curve before loading up.
So many things come into play that I do not think we can give one answer to your question. The aero of the boat itself, drive ratio and engine ability all contribute to the answer. In my testing that session running a Branch Cadillac 542 on a 2.55 drive my wide open was limited at 5,600 which put the 4 blade, 81.5 blades at 2,196. It gave a bigger loaded boat a sports car feel. If SwampThang is on here he has some additional testing experience on JX with several platforms. Not sure if that would be relevant but it’s a resource if your needing more data points.
There is always Dagwood aka Darren at Sensenich, the know all, see all… of factory advanced testing. Always helpful and always a friend.
The JX was like taking your hot rod and putting in a 2,200 stall converter.
As PATO had stated his “best push is 1/2 to 2/3 of his power range”. Some would call this the “snap” while others would call it the peak. The design allows a cavitation or slip down low and suddenly loads and spikes thrust. No doubt a purpose built blade to allow engine platforms the benefit of getting more into their torque curve before loading up.
So many things come into play that I do not think we can give one answer to your question. The aero of the boat itself, drive ratio and engine ability all contribute to the answer. In my testing that session running a Branch Cadillac 542 on a 2.55 drive my wide open was limited at 5,600 which put the 4 blade, 81.5 blades at 2,196. It gave a bigger loaded boat a sports car feel. If SwampThang is on here he has some additional testing experience on JX with several platforms. Not sure if that would be relevant but it’s a resource if your needing more data points.
There is always Dagwood aka Darren at Sensenich, the know all, see all… of factory advanced testing. Always helpful and always a friend.
Airjack
Well-known member
Exactly how I run mine. Seems the best combo for me.