man.. the speed for the engine is depends on how many ports and the pipe set (for using the same fuel).... I think you didn't see any Nova & RB 7 ports .28 engine running in the track... all those .21 can not caught them on the staight road.. so you can not said .28 is slow for now....
may be you are talking about the kyosho .28 engine... but don't forget if it compare with .21 kyosho original p/s engine... both are 3 ports.. .28 can give more bottom end power and you can use 14T iso 13T for the clutch bell.. so their top end speed wl be the similar.
If you think .28 still slow then all those .21 engine.. you can ask anyone in FSY for using STS .28 3 ports engine....one of them is me... you can ask them even all those STS .21, JP .21 , or picco .21 can caught me easy even in straight road or not...
man.. the speed for the engine is depends on how many ports and the pipe set (for using the same fuel).... I think you didn't see any Nova & RB 7 ports .28 engine running in the track... al ...