I just saved a 260z from an untimly junkyard demise by dropping an old 240 motor in to it, the engine starts and runs fine but it's not putting enough juice back into the battery. when I measure the voltage at the (new) alternator (the oposing posts) the voltage is down at around 11.5 volts. my only thought is that maybe there's a major electicle difference between the two systems. any help would be apprieciated.

thanks nick

Go get another alternator. If the new one ya got is putting out less than 12 volts than it's no good. It's not often that a new item comes dead, but it happens.