I used to race the 2.3 in a mini stock on a 3/8 mile dirt track. We had to run stock bottom end. With a 3.55 axle and trans in second gear (2.10), depending on track condition the RPM's stayed between 7500 and 8000. Failures were broken rods first, just below piston pin. Then broken cranks. I broke a #3 rod once, unbolted the head and the block fell apart in 2 pieces. what limits the RPM's is valve train (Valve Float).