Have a new 2017 Road Glide Ultra and put the new Fat Shots on it with 22 discs, but man it sounds quieter than stock.

Anyone else have the new M8 engine with the Fat Shots? How many discs? Open end cap?

I'm sure once I replace the headers it will get a bit louder.

 

the cat in the header breaks up the sound waves- and is also the bottleneck to flow

anything you do now is likely a waste of time.

I use supertrapps lots on a bunch of bikes...

the idea of the disk system is to get and control exhaust gas velocity and direction- and to break up the sound waves- which is probably why you dont notice a huge jump in sound

on my 96" 09, with a no cat header I usually run closed ends caps and 17 disks rt and 12 left.

for your motor probably about 20 or 22 ( 26ish equals the flow through the core) with a closed end cap.

the open end cap will be louder and directional- kinda straight out the back in a line of sight.

the open end cap is counted as equal to 9 or 10 disks when tuning, so you could do 10 or 12 disks and open end cap.

use that antiseize on the threads

in terms of the header a decatted stock header is probably your best bang for buck

Mike

 

You put 22 disk in one pipe or between the two ?

 

I put 22 discs on each side. But I noticed on the new bikes (2017) the right side head pipe coming into the muffler is larger than the left side. Seriously considering a 2-1 with a Fatshot with 20 discs and open end cap.

Yes, I lube the heck out of the threads on both the screws and the inserts.

 

It a pain when they break off if not coated good. I have had both Fatshots and Night sticks liked them both. Only added two disk to each side bikes always ran great and it was different.

 

On my old set of Fat Shots, I had about 45000 miles on them when I traded the bike in. Had swapped out discs and end caps a dozen or so times. They were starting to get stubborn and I knew it would not be long before they ended up stripping out. On that bike, I had best results with 22 discs per side as well with closed end caps. I ran open end caps and 12 discs for a while, but got more "BLAT" than rumble out of it.

 

good info, I just got a set of fatshots and the open end calculations are important for tuning ...thanks

 

Just put a pair on my 2017 Road Glide Ultra as well. Started with 24 on each side but when I spoke to Jeff at Supertrapp, he suggested only running 10-12 per side with open end caps. Currently running the stock head pipe and a little disappointed that it's still not much louder than stock. Had them on my 05 EGC and they were louder. I'm assuming that's because my 05 didn't have a cat nor 02 sensors. Now I'm thinking I might go with their unfiltered head pipe but by doing that, I'll have to add a tuner now too. Lotta $$$$ just to change the sound of a bike!

 

I went with the 11 per side with open endcap from closed with 22discs. First off I lost alot of engine breaking at low speed, Was surprised at that. It ran ok but could feel it was a little looser and more open flow. I put the 22 closed back on after 300 miles. I like the performance better and quieter is what I am looking for. I do have the krome werks open header so the tone is a little louder right there.

 

I should have listened to you. I put the open endcap on with 11 and I didn't like the BLAT so the closed went back on.