Pro Motorsports Engineering pioneered the X-style crossover. The X smoothes out exhaust pulses and yields better scavenging, especially at high rpm. It also quiets exhaust harmonics and improves horsepower. Don't expect a huge gain in power, however. On average, we've seen 5-15hp improvements. Expect closer to 5 hp. Mix the X crossover as part of your horsepower improve arsenal. It's the little things that add up to big gains. On the street, torque is what you want most.