The evolution of the scooter is here, with the Honda Grom. This bike has a 124.99cc air-cooled single-cylinder four-stroke engine with 9:3:1 compression ratio and a SOHC valve train. When we brought this into the HMF R&D Department, we weren't exactly sure what system would work best for it. After countless hours, we came up with 2 different systems: A low mount full system exhaust and a high mount slip on system. Each system has a unique sound, but both pickup 10-15% horse power gains across the board. Whichever system you choose, your Honda Grom is going to sound meaner and accelerate quicker off the line. A great compliment to an incredible machine.