Tested Dirt Bike Products - FMF YZ250F Factory 4 Titanium Muffler with Power Bomb Header Midpipe - Experts on Dirtbikes at Dirt Rider Magazine

We were picking up our modified YZ250F when FMF's PR director offered to slap on the brand-new Factory 4 muffler for us to try out. At the time we declined because the bike was going to be raced at the Big 6 Grand Prix in Gorman, California, and needed a Q muffler to keep it from breathing fire and waking up the bears in the surrounding areas. We did, however, snatch the Factory 4 out of his hands so we could test it after the race.We finally got a chance to install and test the new muffler. To get the full effect of the power, we also bolted on a Power Bomb header midpipe. Installation was really smooth and quick; the hardest part was removing the existing pipe. The Power Bomb was a snap to put on—two bolts and it was mounted. The muffler slid onto the midpipe easily, with the bolt holes all lined up perfectly. The only thing with which we really struggled was the rubber on the inside of the muffler's stainless steel strap. It can be difficult to keep in place while sliding on the strap. The entire installation took 10 to 15 minutes.During our test the bike was a lot more responsive right out of the hole. This was very helpful at the Lake Elsinore track with all its big jumps, especially those right out of corners. The muffler/header midpipe combo seemed to give our YZ250F good midrange power and a lot more overrev, as FMF claims. What we didn't care for was how loud the bike became. We assume this can be easily corrected by just changing the end-cap to a sound level of our liking.Even though this exhaust system gives the bike better low-end response, better midrange and more top-end overrev than the stock muffler/header midpipe, it's the overall design of the Factory 4 muffler that makes it. The Factory 4 not only is lighter and stronger with its titanium can but has a smart new innovative oval-to-round design that allows it to set farther down into the subframe for less chance of damage to the rear of the muffler.The Factory 4 muffler kit starts at $649 and includes the muffler, a Power Bomb header and midpipe, a Power Up jetting kit and a wash plug.DR Tested: 8.5FMF Racing: 310/631-4363; www.fmfracing.com