For those of you who are not familiar with Bill's reference to my earlier Twin Cam 88 recommendations, let me give you a brief recipe:
* Change the cam design to one that closes the intake at near 30-degrees after bottom dead center (ABDC). This starts real power at or near 2500 rpm which is 55 mph in top gear. Either the Screamin' Eagle 204 with a Crane 4-degree advance engine sprocket or an Andrews TW21 performs well. My JM20 cam set is no longer available as Bartels' Performance Products has not ordered any from Andrews for some time now.
* Fit a Screamin' Eagle or similar free flowing air filter. Avoid those filters that have the air turn corners or that directly expose the filter element to the air stream. The Screamin' Eagle, Rivera "Smoothie" or Arlen Ness "Big Sucker" are good examples.
* Use the stock header pipes or pipes that have the same length and diameter.
* Fit mufflers with free-flowing baffles. If you like the traditional shorty dual mufflers then use old style (loud) Screamin' Eagle slip-ons or the same thing from Cycle Shack. For touring riders, there is no better than the SuperTrapp touring mufflers with the performance baffle set; this is the same as Screamin' Eagle touring mufflers & SuperTrapp baffle set mentioned earlier.
* If your engine is one of the carbureted versions, fit a Mikuni HSR45 with the Mileage Kit (Fox Distributing, near Chicago (630) 513-9700. This carburetor greatly improves throttle response and ups peak power between five and seven HP.
* If you have EFI, then you might use the Screamin' Eagle Race Tuner kit or a Power Commander from Dynojet to get the mixtures just right. Stock 'jetting', carbureted or EFI, is very lean in the 20 - 40% throttle range and become more so after the air cleaner and muffler changes. You must re-tune the EFI after the modifications.
These modifications are simple, relatively inexpensive and extremely effective. Hundreds of owners have modified their engines to these specifications and none that I know of has regretted the changes. These moderately altered engines have a very wide power band, much wider than stock. It starts at about 2200 rpm and extends past 6000 rpm. They are also more tractable and pleasant to use than stock. Passing or climbing power in top gear is remarkably improved and a Harley with such an engine will generally blow the doors off most big-cam, high-hor$epower bikes in a top gear roll-on.