Jerry uses a WT Allision and does good on fuel so I heard but he had to change the rear gears $$ Jack has a 740 and the little engine bump up to 370 on HP he doesn't do that great around 7mph about the same as my 8v92 ? why a series 50 they haven't been manufactured in years and balance shafts are getting hard to come by here in the west. We removed a series 50 from a Eagle with a b400 was pretty gutless here good luck