I am still trying to figure out as which RB engine has got top end. Most of the people who use RB engines were talking about amazing low end...

WS7. Any sub model... It is fair to say (though not NECESSARILY the case every time) that more ports=more top end. Usually the number in an engine model name refers to the ports... RB S5 (5 port) Nova P5 (5 port), WS7 (7 port). This engine also has good low end I'm told, but is mostly described as a toppy motor.

RB = longest lasting engine by far. 40litres is minimum if u treat right.

WS7III or the C6 have the most top end on the RB lines. People talk about how good their low end is because they still deliver low end as well as high end. Many "other" high end motors lack bottom end power. For the record, on most (not all) tracks it's low end that gives you a better lap time. I have a couple of S7's, an S5 & C6. They are all great motors. If your track is on the small size you won't need the top end power of either the WS7III or the C6, but they are still fun to have. I have turned better lap times with my S5 on a short tight track than with the C6. With any of these motors (or any other brand as well) getting the "right" pipe has a huge effect on how well the motor will work on a given track.

RB Mike
So if a engine has more ports about 6-7 then it would have a good top-end which is good for bigger tracks.

Like I said in my post, it is a good rule of thumb, but not necessarily always the case.