i have a tz 5 ports in my v1RRR WCE. It is fast. On par with my friend's NovaRossi RR12L5. His engine is almost $100 more. I would definitely get OS TZ 5 ports over Sirio. To me quality is the first priority. Also, I have a OS 1040 pipe. It is about $70 over at rc-toro.com. I don't like Tower. They rip ppl off. I feel OS pipe is best for tz 5 ports. I tried NovaRossi, but I feel OS pipe runs a bit more powerful overall.