Extension Box Or Not

[pachangalpina]

I am getting ready to upgrade my power and currently have my Bravo drives mounted @ 18.5". This is on a non step 38 Fever. I am trying to decide if there is any benefit to add extension boxes that raise the drives or if I should use shorty lowers.

Thanks, Todd

[Marginmn]

It's my understanding that using boxes allows you to run a higher X dimension because the props will be running in cleaner water. However, simply installing them without moving your engines up will actually lower your X, not raise it. I think that is how it works but I am not sure.

I hear that the stelling boxes are adjustable and allow you to raise the X via the box itself. But I have heard that stelling boxes use a ridged coupler and thus do not flex - so they are hard on the drives; while the imco boxes are not adjustable once installed, but they use a rubber coupler and they absorb some of the shock from the drives and actually help prolong drive life.

If you are going to run bigger power then imco shorties and imco boxes might be the way to go.

[Marginmn]

Todd, did you raise the X on your boat from the original factory height?

If so, how much and what results did you obtain?

[pachangalpina]

No, I have not changed the height and I think that they are mounted deep compared to some of the later offerings. With the advances in prop designs I feel that raising them by 2" should not be a problem.

The motors that I am going to install are 625HP so I am increasing by a little over 400HP total. I figure that I am going to keep this boat for a while and I want to plan everything out before I have to redo too many things.

[Marginmn]

I am not adept at measuring X diminsion, but my rigger tells me that the X on my 2000 fever was very deep - 16 1/2. They say I can raise it up all the way to 19 1/2 if I wish as that is where they are coming out of the factory now.

I am thinking about getting one inch by raising the engines up and another 2 inches via imco shorties. Then we can adjust it as necessary.

[DiamondPerformance]

Go with the IMCO box with the three inch rise since you already have the engines out and get the torsional drive shaft , much better for the drives.

[Zanie]

Originally Posted by DiamondPerformance

Go with the IMCO box with the three inch rise since you already have the engines out and get the torsional drive shaft , much better for the drives.

...if you have room under your hatch.
The IMCO 3 inch rise boxes require you to raise your engines 3 inches. oh, then there's the exhaust.

[Back4More]

I went with the IMCO neutral extension boxes and -2 lowers...talked to Reggie and he stated that 12" back runs 7/8" wetter...So I in turn gained 1-1/8" on modifying my "X" dia.
This was on a 1993 42' non-step.
Better check with Fountain...3" is a lot.
I would start with -2 lowers and see what happens.

[Marginmn]

How'd the boat handle with the boxes and shorties? And did you gain any speed with that set up?

[pachangalpina]

Who would I talk to at Fountain?