I ran a RB S7 converted to Turbo head and ceramic bearings. This motor had great top end with the JP3 pipe and good run time around 8-8:30 min mark with a 7.5 carb restrictor. And with the B5 I have not got any good exact run times yet but in this last race i was pitting at 7-7:30 to be on the safe side and with the fuel I had left it will go 8:30-9 I believe. The only complaint I had with the RB motor is a little lack of low end power. Which with the new B5 I have tons of low end and to be honest this motor has never seen a WOT the straight aways at the track I run at is only around 60-70ft. So the B5 has never really got to open up at this track. So this motor is a perfect fit for this kind of track. I already told Mike B. to get me another!!