I was wondering what I might get out of a 2" shorter Imco lower unit.

the boat is a 28 scarab. I currently have a 600 HP motor and running a labed 26 bravo 1 @ 5600 rpm.

The boat has a pad on the bottom and the drive is about 7 1/2 " below the pad.

The boat runs very well but I have to trim to the moon to get her to run fast. I added a Land and sea stern jack which gave me a 9" further set back. The stern jack gave me considerable improvements with cruse speed and top end. But I still have to trim all the way up to get the hull running fast at WOT. I would like to get rid of the stern jack and get a stelling box some day.

With my drive being so low , is it a good candidate for a shorter drive? what should I expect to gain from it? Would I have to change the prop again???

Ask JimV, he had a -2" IMCO shorty on his single engine 27' Fountain, but removed it because if I remember correctly he said it didn't improve his speed so, he sold it (I think). He can tell you about it if you want to call him. His shop number is 616-735-0800.

At 7 1/2" deep with 9" set back you need a shorty. I was at 5 1/2" with no setback and the shorty helped considerably. I would expect 5mph gain at WOT.

I'm not a fan of IMCO though, they haven’t stood behind their drives. Max machine would be my first call.
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I put a 2" shorter imco drive on this year. I have a 27' Avanti. It originally had a TRS drive, I had it re-glassed and put a Bravo I on it, unfortunately, they set it way to low. I also had to trim it up all the way to see any speed and RPM increase.

I ran it a few times so far with good results. Now I just touch the trim and the boat takes off. My prop is way to small now, but I have already picked up 5 MPH's. I get up to 5600 rpm's and there is still more room to go. It is has some difficulty getting out of the hole, but once it is up on plane, it really takes off. I will be trying a larger prop this weekend. I will post my results.

You most likely will have to change your prop.

I saw a 5mph gain with the shortie over a standard bravo. Before you try a shortie, try a Mirage + prop. Then try the shortie, the Mirage and your current Bravo prop. The Mirage might give you the bow lift you need, but you may not be able to plane off with it on the shortie drive.

How did it work out?

have also heard of the larger imco case being slower apples to apples...so what you may gain from the shortie may be lost there..