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Design and content © 2004
Mild Bill (Asshole #27)
StephG (Asshole#108)

Revisions/updates  2006
Schmoe (Asshole #128)

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Hop-up 883 Sportster

The 883 owner has an inexpensive option available to him that others do not. This is the ability to increase the displacement by a whopping 37% for less than $500. The recommended approach is having an experienced Harley machine shop punch out the cylinders and installing Wiseco pistons. It is important that the machine shop uses torque plates when boring out the cylinders.

The Wiseco kit is preferred over the Harley-Davidson stock 1200cc parts, because the Wiseco pistons are weighted to match the smaller 883 flywheels and the dished piston top will raise the compression ratio to 10:1 and allow you to skip head work.

There are a couple of other performance parts that will separate your punched out 883 from a "real" 1200 -- the 883's valves are smaller than the 1200's and the starter motor is not as strong.

Jeffery Stubbins Reports:

"When you bore out an 883, you MUST replace the ignition module. Lots of people are not doing this important step and lunching their cylinders by overheating them with that lazy ignition advance curve on the stock 883 ignition module. Re-jetting the carburetor is also necessary, or you will further overheat the engine due to the relatively lean mixture of the 883 needle, and main jet. The needle jet is the same for each machine (883, and 1200.)"

Another Rider's Report:

[I received the following from George Cohn in the middle of a bunch of other stuff. If anyone knows the attribution, please forward it to me.]

These mods and tests were performed on a 1993 Hugger.

  1. Ran it stock on the dyno
    -- 23HP @ 3000RPM and 40HP @ 5500RPM

  2. Added SE air cleaner and SE Slip-on mufflers ($150)
    -- 25HP @ 3000RPM and 51HP @ 5500RPM (Before MoCo changed the SE Slip-on to reduce noise)

  3. Bored it out to 1200cc using Wiseco pistons and stock heads, replaced main jet with 170mm, opened idle mixture one turn, raised jet needle 0.090 using washers ($600)
    -- 43.5HP @ 3000RPM and 60HP @ 5500RPM

  4. Replaced ignition and coil with SE parts ($150)
    -- 48HP @ 3000RPM and 61.5HP @ 5500RPM

  5. Added Yost Power Tube (Jet Kit, $80) and Keihan jet needle ($15) from 1200 CV carb
    -- 54HP @ 3000RPM and 64.5 @ 5500RPM

  6. Added polished SS Supertrapp 2:1 ($470)
    -- 53HP @ 3000RPM and 67 @ 5500RPM

This weekend my Andrews N4 cam is due to finally arrive, and as soon as I get that puppy installed and sorted out I will run it again on the dyno. My hope is to get 74HP or 1HP/cubic inch

As to changing the Branch Heads or adding larger valves, the tests I have seen show that while I could pull about 5 more HP at the top end, I will lose that much in the mid-range, and that is where I would rather have it!

For further info on Sportster mods, you might want to check out