This article was originally published in the June 2017 issue of Dirt Rider.
It’s not easy these days to get more horsepower with an aftermarket exhaust system. Simply put, manufacturers are building stock exhausts better and better each year. FMF, however, did a great job of accentuating the highlights of our 2017 KTM 450 SX-F with its Factory 4.1 Titanium Full System.
Getting the stock system off of the 450 SX-F is not the easiest thing to do. You have to drop the linkage and remove the shock to let the long stock head pipe wiggle its way free. Once that is over, however, installing the FMF system is painless, and if you want to remove the FMF system for any reason, you will not have to remove the linkage and shock because the three-piece 4.1 system comes off without hassle.
Once on the track you immediately notice better throttle response and improved bottom-end pulling power. Coming out of corners and rolling on the throttle you can feel more meat (or pull) when in soft conditions. Although with the FMF 4.1 system installed it is a little louder than the stock muffler, in return you are getting better pull and a livelier engine character. It makes the light KTM 450 SX-F feel even lighter due to the crisp throttle response. Midrange is increased as I noticed third-gear roll-on was stronger down straights. With the stock exhaust in Map 1 it was tough to run third gear in some tighter corners, but with the FMF system the KTM was friendlier in third gear and could pick up rpm quicker. Top-end and over-rev didn’t improve over stock, but the FMF system didn’t hurt it either. There is plenty of engine up on top, and the over-rev, a standout quality of the orange steed, wasn’t compromised.
I have noticed when running a 120 rear tire that the tire does touch the inside of the muffler, but if running a 110-size rear tire no marks were shown. Riders might get even more rubbing marks if running this muffler with an 18-inch rear tire for off-road conditions. The complete FMF 4.1 titanium system reduces weight of the KTM by another 1.4 pounds (compared to the stock system)! I can get anywhere between 10 to 14 engine hours on the muffler before I need to think about repacking. You will notice the 4.1’s muffler can sound a little rattly when that time comes. Do not try to keep riding with the muffler packing burned out, as you will only break the core off inside the can and cause yourself more trouble.
I am very happy with the performance, looks, and quality of the FMF 4.1 Titanium Full System and would recommend this system for anyone who wants to make their already fast KTM 450 SX-F a little faster and even lighter. It’s a win-win.