The rod/stroke ratio's of b18b/a LS motors and b20b/z motors arent best suited for high revving. They are more known for their robust torque characteristics. The blocks arent casted as beefy (not as much webbing, thinner cylinder walls) as the other b-series vtec blocks as well. By the time you get your motor to safely rev high (oil squirters, oil pump, pistons, rods, studs, girdle, etc from other vtec blocks), you would have spent enough money to have just upgraded to a complete GSR block and tranny, assuming you do your pricing research and shop comparisons. Done correctly though (emphasis on correctly), an LS/Vtec or B20/Vtec can prove itself as a very potent and reliable setup.