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View Full Version : Fatshot vs. Kerker



jbrickley
11-06-2009, 02:37 PM
Hi, Recently ordered 2010 Ultra, and have a delivery date in Dec. Would like to install module, air filter and pipes before I leave the dealer. I'm basically looking for low to mid-range boost. HP gain for both Kerker & Fatshots seems about equal, same with torgue, give or take a pound. So the difference seems to be the tuning ability of Fatshots. However, at 3dB over stock, I'm afraid I'll fall asleep while riding the thing! Kerker aside, perhaps Sceamin Eagle Fatshotz would be a compromise?

bschultz
11-06-2009, 03:31 PM
Sounds like you have done your homework; however the HD Screaming Eagle FatShotZ will provide the most sound right out of the box, due to the open end caps.

warwick
11-07-2009, 05:37 AM
1. I wonder how the SE Fatshots are able to meet EPA dB level with the standard open endcap?

2. It's my understanding that SE version of Fatshots is NOT tunable as compared with the tunable ST version w/ closed endcap. Is that right?

Warwick

bschultz
11-09-2009, 07:54 AM
1. I wonder how the SE Fatshots are able to meet EPA dB level with the standard open endcap?
OEM headpipe w/catalyst.

2. It's my understanding that SE version of Fatshots is NOT tunable as compared with the tunable ST version w/ closed endcap. Is that right?
You can addd and remove discs and swap out end caps (open vs closed) with either version. The HD SE version however would require the use of a special tool to remove the hexhead security screws.

Warwick

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Gary D
11-10-2009, 02:52 PM
I would like to put those screamin eagle fat shotz on my 09 HD Road Glide. Would it be ok to do so with that open end cap? It seems the open end cap is there to allow more sound out of the 2010's with the catalyst. My 09 is totally stock and is going to stay that way, no fuel management or air filter. Do you think that open end cap would cause popping on decel. or lean it out any more than it already is?
Thanks!
Gary D.

bschultz
11-10-2009, 03:57 PM
We found the "closed loop" fuel injection on the newer models to be very accomodating with most of the pipes we offer. Meaning the O2 sensors sends info to the ECM which sends info to the injectors the info to keep the A/F ratio within the parameters of the OEM ECM settings. The 4" open end cap flows for 10-12 discs, so if you removed 10 discs and the closed end cap and replaced it with the open end cap, you would be at the same exhaust flow.

Gary D
11-10-2009, 04:30 PM
Ouch, I'm more confused than before. If I removed 10 discs and the closed end cap, it would flow as much as an open end cap with no discs? The screamin eagle fat shotz come with 10 discs each and the open end cap?
Is it safe to take the screamin eagle fat shotz with the open end cap right out of the box and install them on my stock 09? Or is the open end cap designed just for the 2010?
Thanks again!
Gary D.

bschultz
11-11-2009, 07:14 AM
My bad, I was thinking SuperTrapp FatShots, which come with a closed end cap. Back to the previous answer regarding "closed loop" fuel injection, it shouldn't be a problem. The open end cap was intended to maximize sound on the 2010 models due to low volume caused by the catalyst in the headpipe.

warwick
11-12-2009, 01:27 AM
So using SuperTrapp Fatshots with 10 discs + closed end cap on a 2010 SG w/ cat would be too restrictive?

Warwick

bschultz
11-12-2009, 07:07 AM
No; however they will be quieter than the SE FatShotZ with the open end cap.

baggermanmcp
11-28-2009, 03:35 PM
So, on an 07' w/255 cams running 10 discs should be the "sweet spot" for performance and sound with the Super Trapp Fat Shots closed cap?

Can you give me an idea on what I get, if I purchase a set of open end caps, as far as increase in volume? I used to run the 128-78020 but decided to move to the fat shots for a bit less volume and more flexibility.

Thanks for this great insider forum. Your tech. support is greatly appreciated!

bschultz
11-30-2009, 07:50 AM
You will gain volume (a couple db's) approaching the Kerkers, P/N 128-78020; however a deeper sound.

Gary D
12-02-2009, 01:07 PM
If I'm right, A HD fat shotz muffler with an open end cap and 10 discs will flow the same as a closed end cap and 20 discs? So if I put that fat shotz muffler on my -09- Road Glide, it would be the same as a closed end cap with 20 discs. Would it be too free flowing? I'm asking because you recommend 10 to 12 discs and a closed end cap as a starting point if I mounted supertrapp fatshots. I'm guessing a HD fat shotz muffler with an open end cap is flowing the same as a supertrapp muffler with 20 discs and a closed end cap. Please shed some light.
Thanks
Gary D.

bschultz
12-03-2009, 07:56 AM
You are correct; however keep in mind the HD FatShotZ were introduced for the 2010 models to provide maximum flow/sound with a catalyst equipped headpipe.
Our testing and feedback from tuners with a mildly modified pre-2010 touring models, equipped with an OEM headpipe, found the best performance with no more than 12-14 discs (w/closed end-cap).

Gary D
12-03-2009, 03:49 PM
So putting screamin eagle Fat Shotz mufflers with its open end cap and 10 discs might not be the optimum set up for a stock 09 HD touring model?
Gary D.

bschultz
12-04-2009, 07:17 AM
That's correct.

Gary D
12-10-2009, 05:07 PM
With those pipes (screamin eagle fat shotz) on a stock 09 HD touring model, what would be the best set up?
Thanks
Gary D

Gary D
12-13-2009, 09:13 PM
TTT
Thanks again
Gary D.

bschultz
12-14-2009, 07:09 AM
On an '09 non-California model (no cat), stock (no mods), we found performend best with 8-10 discs and the closed end-cap.

gkriske
01-04-2010, 12:38 PM
Reading this makes me wonder if I've done the right thing with my 2008 Ultraclassic.

I've got a SE aircleaner and SERT with the HD Fatshotz. Stock other than these.

Had my bike dyno tuned and gained about 6 hp and 6 ft/lb torque.

The mufflers have a nice low rumble, just a bit louder than I expected. Not too bad, but leads me to ask:

- should I have gone with a closed end instead?
- if I put a cap on them, do I need to have it re-tuned?

Rather new to all of this, appreciate your help!

bschultz
01-04-2010, 01:18 PM
If you are running the "open" end-cap(s) and are looking for less sound...replace the "open" end-cap with a closed end cap and add 10 discs to obtain the same exhaust flow (tune).

gkriske
01-04-2010, 01:44 PM
10 discs on each side or 10 total?

I presume then I would not need to retune?

Thanks again

bschultz
01-05-2010, 07:07 AM
Per side, no retune should be needed.

Gary D
01-05-2010, 02:22 PM
So the only difference running fatshotz with an open end cap and 10 discs vs a closed end cap with 20 discs is sound?
Gary D.

bschultz
01-06-2010, 07:08 AM
Correct. .

baggermanmcp
10-23-2010, 11:48 AM
You are correct; however keep in mind the HD FatShotZ were introduced for the 2010 models to provide maximum flow/sound with a catalyst equipped headpipe.
Our testing and feedback from tuners with a mildly modified pre-2010 touring models, equipped with an OEM headpipe, found the best performance with no more than 12-14 discs (w/closed end-cap).

bschultz,
I've been running my fatshots with 14 and 12 on 07 103 w/255 cams. I'm jumping to FLHX 2009 with 103 and 255 cams again. Do you still recommend the same 10 - 14 with less on the left side? Isnt the 2009 header unique between the 2008 and 2010 since it's a 2 into 1 into 2 with no catalyst since I'm using fatshots. Help me out! My plan is to transfer the fatshots to the the 09.
Thanks!!!

bschultz
10-25-2010, 07:36 AM
You are correct that the '09 header is unique. Basically the same collector design as the '10-11; however missing the catayst. This design promotes more exhaust flow out the left side than the crossover on the earlier models and can be treated with an equal number of discs on both sides.