Big Bore Kits

58 products

Our Big Bore Kits for Harley-Davidson unlock genuine Screamin' Eagle displacement increases, supplied by Iron City Motorcycles, an authorised Harley-Davidson dealer in Leeds. These Harley-Davidson Accessories kits are built for the latest Milwaukee-Eight platform, covering current Touring models such as the FLHXSE and FLTRXSE alongside 2025-on Softail machines. A big bore conversion is one of the most effective ways to add usable torque and horsepower, transforming how your bike pulls from low revs right through the range. Every kit is engineered to work with the wider Screamin' Eagle Stage performance system and requires ECM calibration with the Pro Street Tuner for correct, reliable installation, so matching the kit to your exact model year is essential. As an authorised dealer, Iron City can guide you to the right combination of parts and tuning. Browse the full range below.