Review on NGK Iridium IX DCPR7EIX Spark Plugs: Harley Davidson Twin Cam (Pair) - 1999-2016 Model Years by Benjamin Michels

2002 HD Heritage Softail. I never believed that simply changing the spark plugs would significantly improve gas mileage, but I've seen a 10-15% increase with these plugs with no noticeable loss of power. And it's not just from replacing old spark plugs, I've been monitoring my MPG since I bought the bike and I'm seeing a 4-7 MPG improvement since installing the NGK. Lowest mileage I've had after battling 50+ mph winds all day, best was on a mountain cruise, but every tank of gas was better than anything I've ever gotten with HD plugs.