2Slow4me

Changed my standard Bravo upper with an X upper and a different gear ratio. Wanted to stick with what I had, but ended up with a 1:36, so thought reducing the pitch of the prop I would end up with the same end result.

But the boat feels sluggish, and does not have the "punch" feel of power, I went from a 28 to a 24, lost around 5 MPH, but feels gutless.

Is this normal? does the X version use more HP? (I turned the drive shaft before installing, and it turned very easy)

bor

iTrader: (1)

My experience is that you only go back to 1.36 when you run out of prop so when you turn a 34-36" otherwise you have no benefit from it only the downsides you experienced .

F-2 Speedy

iTrader: (6)

It takes a bunch of power to pull a 1.36 28p, I would think in the 700hp range depending on the hull and weight....what rpm are you seeing ?

Tinkerer

It takes a lot of torque to spin a 1:36 drive.
I had the same issue with my Daytona when I went to the -3 shortie 1:36 ratio. The old drive was a -2 shortie 1;50 ratio.
I figured that raising the prop an inch would help but it didn't. I lost 600 RPM ( from 6000 to 5400 )
The reason I did this is that I knew that I was going to build the 598 the next year.
The 598 has the torque to spin it.
Same prop I am now turning 6100 RPM

2Slow4me

Why does it take more HP to turn the 1:36? Based on theory, the 1:50 with a 28 is the same as the 1:36 with a 26.

I'm only running a stock old 454 magnum (370 HP) with CMI headers (so maybe 400 HP)

Last weekend, I ran the 24 70 MPH @ 4,500 and when I pushed past that, the motor felt like it was bogging, so I didn't push past that.

Its a small 20'7" very light eliminator V bottom with pad, and it fly's (flew) and rides like an outboard, very light very fun. Now it feels heavy like the boat gained 500 lbs...

jeff32

My 97 sunsation 32 ran 1.36 with 23 mirage 3 blades on hp500 carbed motors and was really fun to drive, maxed out around 82-83 mph

you might want to try a 3 blades? Or lower your 4 blades pitch?

Or simply up the HP !!!

Tinkerer

With the 1:36 ratio the prop spins faster for the same engine RPM that takes torque. Your stock or warmed up engine doesn't have the torque to spin that prop.
And someone told me it was 600 RPM difference between a 1:50 drive and a 1:36 drive with the same prop.

Griff

Going from a 1.50 to a 1.36 is generally about a 600rpm reduction or 3" of prop pitch.
I have 1.36's on my 32 AT with 502mpi's and spin 24 Bravos to 5100 rpms.
Its always had the 1.36's so I don't have anything to compare it to, but it accelerates well and never feels sluggish.

dereknkathy

at least you are in the prop neighborhood where they can sometimes be borrowed to try out. somebody on your sand bar has a 21 or 23 mirage. I guess the 1.5 upper is dead, or you woulda switched back?

Mbam

I general a higher numerical ratio is faster. The prop turns slower so less mechanical energy is wasted turning the prop. The difference in RPM just from the math between a 1.5 and a 1.36 should be roughly 10% of your RPM with the 1.5. But it can be a liitle more as the boat is going slower also.

If you want to play with pitch/ratios you can use our calculator

Prop Slip Calculator