FMF Powercore IV-2 modification


I got the new pipe and its way too loud! Baja designs suggested I repack it due to their theory of loose packing in the pipe. I took it apart and added packing. Result? Maybe 5% quieter. I guess something is better than nothing.

The process is as follows:

Leave the pipe attached to the frame, but loosen the pipe clamp.

Take the four screws out and tap the muffler barrel out with a wide aluminum blade. It does mess up the barrel's edges slightly.

Inside you'll find the dcore is wrapped in steel wool with a fiberglass blanket around it. At both ends, there is a small fiberglass strip that seals the muffler. Overall, I'd say ther is plenty of room for more material around the core.

Take it all apart and then add aftermarket fiberglass around the core. Use masking tape to hold it. Then wrap it with steel wool and the fiberglass blanket. Keep using tape to hold it together.

Slip the muffler barrel back on. You may have to tap the last inch or so with a rubber mallet. Install screws.

Not too difficult, but for the money we pay, it should be right from the factory.

Good luck


I agree with you that the money we pay we should not have to do this type of modification. I also have purchased the new FMF Powercore IV-2 and noticed no improvment in power over the uncorked stock unit and only slightly quieter. For me this mod was a complete waste of money.Even repacking this unit you will still not pass sound check as it is still blows 103db at idle. FMF and very good deceptive marketing. Complete junk.

Wow! Mark Trains $5 home made exhaust end cap is looking pretty good to me.


Help,I've just ordered the Power core four/2 and the Hi-Flo header to go along with it. The guys at FMF said I could expect a 15% gain in Horsepower. Does anyone out there have any experience with this? Also, Clark thanks for the tips on re-jetting I'll let you know how it works out.

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