What size mids?
 

I've got two 20" GT 200s which I can dual mount and two Merc 275-Coswoths which are 20 & 25". I thought I could mount the 20" mids right on the transom and maybe mount the 20 or 25" on a transom bracket and or a jackplate. My mech told me that he believes I need a 30" to mount as a single and 25" to mount twins, is this so. I know airdog mentioned that I use the transom bracket he used, 24" heavy duty. But I'm not sure how that would look W/O closing the motor well, which I hear is a lot of work.
Any recommendations?

Mount the 25" Merc 275 in the center and then mount the two 20" GT's on either side of it.

Use the 20" Merc for parts when the other one breaks.

:drink:

The correct size for twins would be 20" mids.

The correct size for a single is a 25"

You Mechanic is correct. A 30" mid will put the cavitation plate level with the bottom of the hull. However, the performance is better with it at 25" and there is no blow out or cavitation.

I ran a 20" mid single engine. That would cavitate a bit with the chopper prop.

If I had a recommendation, it would be to run the twin GT's, unless you want a single engine, then run the 25" Merc on the transom or the 20" Merc on a 17-18" bracket.

Thanks Chris, my plan is to mount the twins on the transom. with the 2.7 heads and the jetting they should put out a good 235 hp each, they also have 6500 rpm power packs. I'm getting the Scarab back this week and will sand before painting, the power wash got about 95% of the bottom paint off. I should have the Banana ready for painting in about two weeks, spoke to the guy last week he said he's slow and to bring it down.