Stock HD 103

[kgchris]

I have a 2012 HD limited with the 103 motor, all stock. I think I want to add the supertrapp Fatshots. Is it possible to tune mainly for exhaust tone (loudness) if I'm not too fussy about the changes in torque or hp? If so, how much variation is possible without adverse effects? Also if i am performance minded what usual increases in performance can one expect without doing any other modifications other than exhaust?

[bschultz]

More discs, more flow, more sound; however keep in mind the catalyst in the headpipe soaks up a tremendous amount of sound. Staying between 10-16 disc should net you a 5-10% HP/TRQ gain. More or less may affect top end and/or bottom end performance.

[kgchris]

The 10 - 16 disks would that be with the open end cap or closed? I may go with the HD FatshotZ.

[bschultz]

Closed.

The HD Screaming Eagle FatShotZ is a good option.

[kgchris]

Am I correct in my understanding that with the open disks one would normally get by with 10 disks less to equal the closed end cap configuration performance? If this is true, do these "equivalent" settings produce the same loudness or is the open end cap and 10 less disks one a little louder?

[bschultz]

Am I correct in my understanding that with the open disks one would normally get by with 10 disks less to equal the closed end cap configuration performance? YES, 10-12 (4") discs If this is true, do these "equivalent" settings produce the same loudness or is the open end cap and 10 less disks one a little louder?

The "open" end cap will result in MORE sound.

[kgchris]

Update: I bought and installed the Screamin eagle fatshotz. Like the sound, love the look. So....if I understand your earlier posts then,

1. I might want to remove some disks , (like most of them) since this has the open end cap with 10 disks and your first reply indicated i should use 10-16 with closed endcap? Correct?

2. If so, why would Harley send the out this way and lock them down?

3. Reading the description for the HD tuning kit on your web site it says something about race only, yet it would seem to me that using the closed endcaps and more disks to get to the 10 - 16 you recommend would give mellower (more epa compliant) tuning. Or what?

4. If I leave the Fatshotz just like they are now am I running any unnecessary risks and if so why again would Harley sell something that isn't the best config for stock and then not want you to change it (locking screws)?

5. Am i making any sense here or am I misunderstanding something?

Thanks for all your help. Love the support and the pipes.

[jeff]

Update: I bought and installed the Screamin eagle fatshotz. Like the sound, love the look. So....if I understand your earlier posts then,

1. I might want to remove some disks , (like most of them) since this has the open end cap with 10 disks and your first reply indicated i should use 10-16 with closed endcap? Correct?

2. If so, why would Harley send the out this way and lock them down?

3. Reading the description for the HD tuning kit on your web site it says something about race only, yet it would seem to me that using the closed endcaps and more disks to get to the 10 - 16 you recommend would give mellower (more epa compliant) tuning. Or what?

4. If I leave the Fatshotz just like they are now am I running any unnecessary risks and if so why again would Harley sell something that isn't the best config for stock and then not want you to change it (locking screws)?

5. Am i making any sense here or am I misunderstanding something?

Thanks for all your help. Love the support and the pipes.

you can run the open end cap with 10 discs because you have stock head pipes with a cat which creat muffling and back pressure. The mufflers you have are for 10 and later bikes which of course have the cat. If you put those on a non cat bike they would be much louder.

[kgchris]

On a new Harley like this is it really possible to tune based on disk or plug color or will the o2 sensors and ecm adjust for almost all changes? I can wipe some soot from the portion of the disks that show. The plugs look good, some light soot on the rim of the front plug. Gas mileage is kind of crappy - 35 mpg, but only 700 miles on the bike.

[bschultz]

You still control exhaust flow and sound; however the "closed loop" fuel injection introduces a variable, keeping the AFR within set parameters. Plug burn and disc color are less affected by the number of discs, within an envelope, then an "open loop" or carbureted power plant.
Maximum performance can still be accomplished by finding the correct number of discs for YOUR particular motor combination.