I have two RB x-12's I use in off road. I like them very much. I just got a V12 also for off-road. This isn't going to make any sense, because they are very similar, but I am quite disappointed with the engine. Lacks top end. I have not tried it in my onroad car, but I have been very fast with the novarossi NS12S3A1. This engine is not much more money than the RB.