ORIGINAL: lfinney
many sport engines run ABEC 2-3 bearings, going to a ABEC 7 bearing will give rpm gain too, the higher the number the greater the clearance, check out what nelson,jett, Mb and others use..often ABEC 7 spec ....FWIW
I think you may be confusing ABEC with the clearance spec. Nearly all engine bearings are ABEC 1-3. A few are ABEC 5. None will be ABEC 7 as there is no advantage to those and the cost is significantly higher. Clearance for 99% of engines will be CN (between C2 and C3). High performance engines will normally have C3 or sometimes C4 clearance.