B) NAMBA has opened it up allowing RS101`s in both there X Classes & Twin classes. Meaning you can race a RS101 Twin in both If you are NAMBA........ I like the fact it allows the classes to grow......... If I lived in Florida racing area I would have nothing but RS101`s. However those Florida guys Do get a lot of Fast laps out of the VAC-91 engines... The VAC91 is the best engine choice IF you are re-powering a older boat, They dont burn as much fuel as the Rs101 & the older boats are limited on how big the tanks can be. Most (36oz total)..... The New RR twin hauls 50-51 oz`s & a set of Modified / Thirsty Engines will need every bit of it. Especially if the Air is Good/cool & you have to run Rich needles. Many benefits to the NEW RR TWIN of Mid 2010 to Current Design. Ralph can feel you in if you have questions? Can Haul More Fuel, Handle Bigger more Powerful Engines & Handle the Race Chop @ Higher Speeds. If you are buying a New Boat the RS101 engine choice is a No Brainer........... However if you are repowering a existing older Twin boat with limited fuel tank sizes? You are limited to what you can achive........ B) B)