HP vs prop RPM increase math gurus

[Blackmagic94]

Ok so planning on swapping the bumpsticks in my Cig this year from a flat tappet to a solid roller setup to bump the power



So lets say the following


if current set up is


479@4250 rpm=59 mph with a 28 pitch 3 blade clever on the SSM3 drives at 1.59


If the new cams made 508 at the same rpm
but made 83 more HP at 4750 rpm
and 106 hp at 5250 rpm


Would that be enough rpm to push pass that 4250 rpm threshold it currently has vs the prop and would i be able to get to the peak rpm of this cam at 5250



Or


How much hp to get a 100 rpm increase rule of thumb lol

 

[coolchange]

So you want a 100hp to give you 1000rpms

 

[Teague_JR]

so your current WOT rpm is 4250 at 59 mph?! Obviously you are too tall on prop. To see if the new setup might pull it I need to know:

What did current engine setup make max HP and Torque at what RPM? what did the new setup make?

edit: I reread it more carefully you dont know numbers yet this is theoretical. I dont think swapping cams will pull those props. Swapping cams will get you more horsepower and RPM head room on top. If it will only pull them to 4250 now, you would need a supercharger to make the mid range power increase to pull them further....

 

[HST4ME]

The hell is the diameter of those props? Slip is high for that set up, but your kinda stuck at the boat hasn't loosened up speed.

 

[SBMech]

40HP is not going to get you over the "too much prop" hump you are stuck on IMO.

 

[Go-Fly]

Back in the late 70's I asked Big daddy Don Garlits how much did it cost to make a car that goes 255mph. He said it takes a million dollars to get to 255 and another million to get to 256. I always think about this when I try to squeeze a little bit more out of something. Start with the build and spend money on props. One thing I've learned over the years, some boat hulls can only go so fast. Disclaimer: Any statements in this post excludes jet boats.

 

[Blackmagic94]

so your current WOT rpm is 4250 at 59 mph?! Obviously you are too tall on prop. To see if the new setup might pull it I need to know:

What did current engine setup make max HP and Torque at what RPM? what did the new setup make?

edit: I reread it more carefully you dont know numbers yet this is theoretical. I dont think swapping cams will pull those props. Swapping cams will get you more horsepower and RPM head room on top. If it will only pull them to 4250 now, you would need a supercharger to make the mid range power increase to pull them further....

The cam swap will increase hp and torq from 3750 and up. And a decent chunk.

 

[Blackmagic94]

The hell is the diameter of those props? Slip is high for that set up, but your kinda stuck at the boat hasn't loosened up speed.

12.5%

 

[Blackmagic94]

Cam swap comparison

 

[HST4ME]

548's through 1.50's, 28's on a 35.. the 35/38's with #3's were quite popular around here back in the day and posted considerably better numbers than that. I'm not dogging on your rig but you have a bannana in the tail pipe somewhere.

 

[Blackmagic94]

548's through 1.50's, 28's on a 35.. the 35/38's with #3's were quite popular around here back in the day and posted considerably better numbers than that. I'm not dogging on your rig but you have a bannana in the tail pipe somewhere.

Agreed. The camshaft profile sucks.

 

[Blackmagic94]

As you can see from the graph it a small pickup at 3700 rpm, and increases to a huge pickup after that.

 

[Teague_JR]

Agreed. The camshaft profile sucks.

yeah even if the cam profile sucks and your HP has plateau-ed at 4600... getting the right cam in the motor isnt going to bring WOT RPM from 4250 to 5500 if your engines are actually in decent health. I would leak them down before digging into them to make sure that all 16 cylinders are at least decent..

the cam swap is a no brainer. Then run it with your current set up and see what happens.

 

[Blackmagic94]

yeah even if the cam profile sucks and your HP has plateau-ed at 4600... getting the right cam in the motor isnt going to bring WOT RPM from 4250 to 5500 if your engines are actually in decent health. I would leak them down before digging into them to make sure that all 16 cylinders are at least decent..

the cam swap is a no brainer. Then run it with your current set up and see what happens.

Motors are rebuilt.