Grand Prix Slip-Ons take Firebrand’s aggressive styling to the next level. Don’t be fooled by their good looks, the Grand Prix Slip-Ons are not only for show. Inside the 4” muffler bodies are free flowing, stainless core baffles wrapped in dual-density packing. Engineered for your Harley-Davidson Twin Cam motorcycle, they deliver increased performance, and a sound so deep you can feel it.