Pick your year and look at the fast facts. http://www.fourwinns.com/customer-service-catalogs.aspx

I see this is an old thread...

http://i1268.photobucket.com/albums/...ps9aaiscan.jpg

Yup, twin small blocks will use the same fuel or only slightly more than a single big block that is overworked, plus you have all the work to convert to a single, and in the end you will have a boat that nobody wants to buy because it will be a single engine turd