how can I upgrade a 2008 Road King Screaming Eagle

[FishHunter]

Have heard tell that the PC V is a pretty darn good unit.

 

[jonny oz]

the best bang for your buck will be to rework the heads you have, like mentioned, and get high comp pistons, a more aggressive cam and custom dyno tune. it already has a good air cleaner, but if you're looking for max power get a 2-1 system (I hear alot of talk about D&D, thunderheader, v&h propipe when it comes to power)
Also, I think i read somewhere that the SE110 DOESN'T have roller rockers? I would get some of those in there too.
the SE 110 engines have a problem with blowing the rear head gasket, and this problem has been linked to excessive heat. get a jagg oil cooler installed, and for sure run full synthetic in all 3. (FYI SYN3 is not a full synthetic, just learned that today right on this forum!)

 

[FishHunter]

Much room for improvement with cylinder head mods,(to include spin-drop to correct the squish) cam change, exhaust improvement.
HUGE power gains.
But with case boring, the engine can quickly go to a 117", and with all of the above included, even more can be on tap, at any time, in any gear.:s

 

[Mainah]

One word: Nitrous!

$400 to $500 for a 30% to 40% power increase, easy installation and will blow away mods costing 10 times as much.

Just remember, use it sparingly unless you also strengthen the bottom end, A LOT!

 

[FishHunter]

Laughing gas is illegal in a lot of areas, and has created more harm than good, usually.

Much room for improvement with cylinder head mods,(to include spin-drop to correct the squish) cam change, exhaust improvement.
HUGE power gains.
But with case boring, the engine can quickly go to a 117" or 124", and with all of the above included, even more can be on tap, at any time, in any gear, with out fear, of any type of power loss whatsoever.