i have scarab 22 that i put a -1 imco and is much more stable . I have a chance to trade it for -3 imco. what is the give and take of it, maybe more speed or not . does anybody know the result . dont want to go the wrong way
help

Depends on what your x dimension is.

And depends on the boat, how high you can go.

I have a similar boat, a 20'7" Eliminator, and when I redid the stringers, I remounted the drive, and raised it around 3-3.5", so from the cavitation plate 1" below the boat, to 2"-2.5" above.

Made a HUGE improvement, went from a boring I/O turing a
25" mirage, to a fun boat that would fly and lift turning a 28" bravo gaining 10 MPH.

The only thing, without the 4 blade, it would cavitate like crazy, and you could not turn the boat.

What height is your cavitation plate @ now?

What prop, speed & RPM before the 1" imco?

Trade it you will have to reprop, If you experience problems with it blowing out PM me there are some things you can do so it wont.

The -3" IMCO takes a special upper unless you want to cut your cavitation plate.

You won't get a -3 on a Bravo 1 or XR without running a small diameter wheel (which will make it hard to get on plane) or cutting up the back of the drive. The IMCO drive has a stepped up cav. plate to clear a -3. You can clearance the drive to clear it and make some plates to cover up the holes you make, but it is a bit$h to do. It took several hours to get it right.
Eddie

Its not that diffucult to make a -3 fit a bravo upper so you can use bigger diameter props. The only difficult part is IF you do experience problems getting on plane and extending the prop hub doesnt correct it you have to fab a cavitation plate to fit. Ive got a pattern and a local machine shop that makes them for me if you need.

I always just used the IMCO cavitation plate that comes with their shorties. You had to shim it up some to clear on -3 though.

If you want to do the mod to your drive, go for it. You can space a shortie down, but not the other way around.
What prop are you useing with your -1 Imco? Tell us a little about the setup, engine ect. top speed and so on.

Just swapped my -2 to -3"s on sunday. All u have to do is cut a notch in the upper and put a rubber bushing on the Imco cavitaiton plates, looks factory.

I run 30 pitch labbed bravo 1> The motor is hp 465 with 731 cam , dart intake , grumpy jenkins merlin steel heads , glm exhaust hardin raiser ( 4 inch ). I have run 82.5 on gps and i have drew marine side winders on the drive with shot gun mufflers . I turn about 5100 , rev limiter is set at 5350 . I think i am over proped but it work well and gets on plain easy .