pardon me if this is a stupid question. is an extender box the same thing as a stand off box? and what is the benefit of moving your outdrive away from the transon?

They are the same. The advantage is to move the prop back into cleaner water and therefore allowing a higher X dimension. (raise props, less drag)

Having the prop back further also sets it deeper into the water when plaing off. Usually is the prop cavitation when planing that is the determaning factor when setting the x-dim. With the box you can now go significantly higher.

thanks guys. can someone please explain the x dimension.

Just did my TG change from transom mounted TRS's to Ext. Boxes and No V's . Jury's still out on how much it improved. But then again I changed so much at one time (blower eng's,X dim's, weight) hard to say what did the most improvement................

The x-dimension is simply the depth of the prop in the water. Deeper for crusiers, working boats, ski boats, higher for speed boats.