rod length/strength. head design, cams, and power production.
b18b stops making power around 6.5-7k while the b18c stops making power around 7.5-8.0k because of the head design and cams...no need to rev any further if it stops making power.
Yeah, that and it's leet.
Some say that his politics are terrifying, and that he once punched a horse to the ground...