FMF Gold Series Fatty Pipe & Powercore2 Silencer

What it is

FMF’s Fatty Gold series pipe a bolt-on replacement for the stock pipe and silencer combination. It is claimed to broaden the powerband, increase power and give better throttle response compared to the stock pipe/silencer. On the KTM the pipe and silencer can be used individually or paired. Made from carbon steel with a nickel plated finish for maximum durability, FMF Racing’s Tru-Flo stamping process is the evolution of 35-years of pipe making.

How it works

The pipe is truly a bolt-on application on the KTM and takes all of 10-minutes to install. It even comes with the O-rings. On most bikes you will have to adjust the mounting brackets for the best fit, but this is how you should install any pipe. On the Powercore2 silencer, there is a second mounting bracket and on the 2008 KTM 144SX we tried it on where the stock muffler has only one bracket. The frame has the mounting hole for the second mount but you’ll need the additional rubber grommet, bolt and washers. We ran it with only the single muffler mount with no issues but the second would make it that much more secure.

The first thing that you notice is that the shape of the FMF expansion chamber is a little more bulbulious than the standard pipe but it does not stick out or get in the way of anything. The sound of the bike has a crisper ring and just turning the throttle there is a little more snap with each pull. On the track the power difference is noticeable especially in the upper mid-range where the pull is pronounced over standard. It is actually where you’d really want the bike to be doing work, right in the meat of the powerband. From the bottom to the top the bike feels like it is making just a little bit more power and torque at lower RPMs than the stock setup except in the upper mid-range where it is significantly more. And with that surge comes a slight feeling that the top end is not as strong as the standard bike but this is deceptive due to the boosted mid. With that stepped power it could be argued that the stock pipe and muffler delivers a smoother overall delivery. But getting some of that smoothness back, say on slippery tracks is as easy as switching back to the stock muffler which keeps most of the gains just smoothes the surge in the middle. Running just the muffler alone with the stock pipe seemed to free up the throttle response but does little for the amount of power. Another good thing about this FMF pipe is that they didn’t lose the good overrev feeling on the KTM and it’s sign-off is not sharp or abrupt.

The FMF pipe liked to have a little more fuel than the stock setup, depending on the track/temperature/altitude it wanted a one-size richer pilot and/or the needle to be raised one position richer than the stock pipe. Without the jetting, the pipe can make the bike detonate, which is something to watch for on all small-bore KTMs. The muffler (alone) did not seem to affect the jetting. On the sound side the FMF may be just a little louder to the ear trackside but it is not enough to worry about. On the durability side the metal on the FMF feels just a little bit thicker than the stock pipe and it should hold up to dents a little better too.

The stock KTM two-stroke pipes are hard to beat for smooth power and lots of clean overrev. But FMF went after boosting where they could without sacrificing anything and they achieved that. As a modification solely for power the pipe is worth it if you need a little more without going to internal engine modifications. But as a replacement for a dented or smashed stock pipe it becomes a value compared to a $400 replacement from KTM.

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