I would have to say, if your track is BIG, LONG enough for the engine, SIRIO EVO 3 will have the edge over the OS 12 TZ, no doubt............however, if your track is not 250' plus or longer, I doubt you can tell the SIRIO is any faster then the OS TZ....at least, the OS will be as fast, because you cannot actually squeeze out all the SIRIO extra power............

Not to mention.........after you see this, I doubt you will want to use SIRIO engine....yes, their carb sucks, now, add one more well known problem of SIRIO...very similar to MEGA engine if you don't know when to replace engine parts........

So, I would definitely buy the OS 12 TZ (3 or 5 ports, both are fast)....tower carry the entire engine inside and out, P/S set are $50 total......I can garantee you that EVO3 piston or sleeve iitself is $50 each.....if you can buy them seperately....LOL