Jeremiah 29:11

Generally, a tuner is a programmer and a under pulley is the same thing as a underdrive systems, increase power, but, the drawbacks depends on what it does to do it. underdrive, as in, smaller pullys, reduce rotating mass, thus, force required, thus, higher power output. BUT, can cause excessive wear on powersteering systems and alternators, which are being spun at faster than normal speed. Lightweight pullys better alternative, still reduce mass, thus increase power, but, dont reduce rotation distance, thus, dont effect anything else. generally more expensive, but the 'proper' way of doing it. underdrive, often the cheap way out.