My ‘17 Road King with the 107 has a Fulsac head pipe and K&N breather. Dyno tuned by Jason at C&S in metro east STL. Bike runs great, no issues. I had CFR’s and it had a very noticeable dip in the 2,000-3,000 RPM range. Noticeable in both the dyno graph and the butt dyno. I went with 2” Fulsac cores in the stock muffler housings and that torque dip is definitely gone. However, the sound is very anemic. The sound is just about like stock. I have respectfully named the bike a Yamahog. With that said, is there a muffler set out there that has enough back pressure to keep the torque in the low rpm band and make it actually sound like a Harley?
The low-end TQ dip with the FS header and CFRs was caused by the lack of restriction (resulting in a lack of "back pressure") in that setup. Of course, it also gives plenty of volume, like racing pipes.
Now, with the non-cat FS header and the 2" baffles, you still have a low-restriction header but a semi-restrictive muffler. It gives enough restriction to maintain TQ at the low end, but naturally it loses volume.
The upshot: the laws of physics require a certain amount of restriction to keep the low-end TQ, either in the header and/or the mufflers. Since the mufflers are designed specifically to reduce sound volume, the solution is to get a more-restrictive header and a muffler designed to "tune" the sound and not reduce the volume so much. A good setup would be the stock header paired with the CFRs (or any megaphone type muffler; mine only cost $185--enough restriction to keep low-end TQ, with mufflers that have good quality sound and high volume. This will get you much closer to what you want, although it won't be as loud as the FS header with CFRs.
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Topic: M8 mufflers that don’t kill bottom end (Read 5814 times)