From the Boutique:

Typical Staged Sportster Engine Upgrades

Stage 0: Stock

HP=40 for 883, 50 for 1200 (average)

Stage .5 (also known as "The Harley Tax"): Stock plus:
SE Air Cleaner(1)
SE Slip-On Mufflers or equivalent(2)
Rejetting (DynoJet, Yost or just jets)(3)

HP=50 for 883, 60 for factory 1200(4)

Stage 1: Stage.5 plus
883/1200 Conversion for 883s(5,6,7,8)
SE Ignition Module or adjustable one(9)

HP=60 for 883/1200, 65 for factory 1200

Stage 1.5: Stage 1 plus
Andrews N2 cams (mild)(10)

HP=65 for 883/1200, 70 for factory 1200

Stage 2: Stage 1.5 plus
Andrews N4, N8, or SE bolt-in cams instead of N2(11)
SE S1 Lightning or other bolt-on +/- 10:1 heads(12)

HP=75

Options: 2 into 1 header system, add +/- 7 hp(13)
SE carb (or equivalent), add +/- 3 hp(14)
XR750 (or other) valve springs, no gain(15)

Stage 2.5: Stage 2 plus
Professionally ported 10:1 or higher heads
Matching (to head) domed pistons(16)
XR750 valve springs or SE cam kit(15,17)
2 into 1 header system(13)
SE,S&S Super E, or Mikuni HSR42 carb(14)

HP=90+

Options: big valves (big twin size), add +/- 5 hp(18)

Stage 3: Stage 2.5 plus: (or:)
Big-bore cylinders and pistons and/or
Stroker kit and/or
Nitrous injection and/or
Supercharging

HP=?

Options: many

Notes:

(1) Highest flowing air cleaner available, also the cheapest. KuryAkyn and Dragtron don't flow as well and are much more expensive.

(2) Cycle Shack makes SE slip-ons and sell almost identical models for a little less without any Screamin' Eagle script stamped into them. Using a 2 into 2 exhaust system which eliminates the crossover tube may result in both some hp loss on the top end and/or lower rpm torque. Drag pipes, even with "power cones," "torque valves," and/or baffles, cause significant loss of low/mid rpm torque. Recommend avoiding them.

(3) The only thing that matters here is getting the jets correct. A #45 slow jet, and a #170 main jet for 883s, or #180 main jet for 1200s, or #200 main jet for '98 1200 Sports, in Stage .5 ($15 total) will do 95-99% of what the high-buck kits do. Jetting appropriate for one stage may not be right for another. Addition of any performance equipment such as cams possibly requires rejetting.

(4) A 50 hp 883 is NOT the same as a 50 hp stock 1200. The latter has 30-40% more torque at lower rpms.

(5) 883/1200 conversions which raise compression ratio to 9.5:1 (HD, Wiseco, JE) have more torque than factory 1200 at the low end but the smaller valves limit top end power.

(6) The all-HD conversion requires grinding out the heads, which eliminates squish and may cause pinging. The HD pistons are much heavier than most others (Wiseco, JE, KB), which increases vibration.

(7) Requires 1200 ignition module. Also see note 9.

(8) Forged pistons (Wiseco, JE) may be used from Stage .5 up. They are stronger than cast pistons (HD, KB), better withstanding ping and high-rpm use, however, they are usually noisier than cast.

(9) Factory 1200 ignition module rev limits at 5,200 rpm. More power can be had above that even with smaller 883 valves. The non-adjustable SE module is the low-cost solution for raising rev limit, but that is all it does. Some aftermarket modules offer selectable advance curves and rev limits. Single fire ignition systems offer smoother idle and low-rpm performance but no significant hp gain.

(10) Significant torque boost at lower rpms and moderate hp boost at higher rpms.

(11) Significant torque loss at lower rpm with these cams if +/- 10:1 heads aren't used, moderate loss of low rpm torque with +/- 10:1 heads. High-rpm cams and high-compression heads should be done together.

(12) Other vendors offer bolt-on head solutions. Professional speed shops can modify 883 heads for high-compression and high-rpm use with 1200 size valves. With either bolt-on or modified 883 heads, the difference between 883/1200 and factory 1200 disappears at this stage.

(13) SuperTrapp, Bartels 2-stage, or Thunderheader 2 into 1 exhaust header system. Care must be taken in tuning SuperTrapp to avoid a loss of torque around 2,500 rpm. May be used in Stage .5 up.

(14) SE, S&S Super E, Edelbrock QSII or Mikuni HSR42 carb is slightly more responsive than stock CV carb, but care must be taken not to overthrottle.

(15) Heavier valve springs protect against valve float at high rpm, but increase wear on valvetrain. Not required for occasional use of rpm up to 6,500. Should be used for extended use above 6,000 or rpms higher than 7,500.

(16) Domed pistons provide large squish areas allowing higher combustion pressures and power with less risk of pinging.

(17) The cam in the SE kit is the most radical of those listed here. The intake closing is the latest resulting in the highest compression loss. The lift is the highest, requiring heavier valve springs and valve to piston and valve to valve clearance should be checked carefully.

(18) Larger valves increase flow in proportion to the increase in diameter; however, with more flow area comes reduced velocity, negatively impacting low rpm performance.