IF THE ENGINE MAKES ENOUGH POWER TO GO 140 MPH THROUGH THE TRAPS IT WILL ONLY TURN 6934 RPM WITH THE 4.86 AND A 33IN TIRE(DOES NOT FIGURE TIRE SPIN),THE 4.86 WILL BE LESS APT TO SHAKE THE TIRES WITH THE SHORTER TIRE THAN SAY A 4.30 OR OR 4.11,MY PERSONAL OPINION IF THE ENGINE HAS A GOOD VALVE TRAIN,GOOD RODS AND CRANK,AND A PRETTY DECENT BLOCK,I WOULD LEAVE THE GEAR LIKE IT IS OR GO 4.56,I TURN MY 632 7800-7900 BUT IT GIVES VALVE TRAIN TROUBLE ONCE IN A WHILE