novas are considered to be the best engines arround , though os speed are almost new into the racing category engines and they have done it very well so far...
i've seen the 353 and i own one OS 12 speed xz.Both engines run good ,actually really good.OS is much cheaper and the only thing it needs is a conrod every 5 litres , although it has a new type of conrod which is considered to be much stronger than the one in the spec 2 , though i don't wanna risk it...
racing the angine couple of weeks ago , many people were amazed about the XZ that goes so fast , although there were all type of brands in the race like RB , NOVA , SIRIO , MAX POWER MF , PICCO.
So i choose OS XZ .this engine combines everything...SPEED , CHEAP , STRONG