Whilst the regular Evolution Sportster 883-1200 conversion remains the best "bang for the buck" of any Harley-Davidson performance upgrade, there is a lot of additional power to be had by porting the existing 883 cylinder heads. The head castings and existing valve seats have sufficient material in them to allow both the installation of the larger valves from the earlier ('88-'03) 1200 heads, as well as a thorough and well developed reshaping of the ports. The small diameter 883 "hemi" combustion chamber is also used to good effect, as when coupled with the larger cylinder bore size of the 1200 (3 1/2" instead of 3"), a substantial quench area is created. These reworked 883 castings give a far better result than trying to rework the older XL1200 heads, as there is already too much material removed from the wrong places with these.
Because the valve stem protrusions remain as stock, and the heads are only decked sufficient to clean them up and balance the chamber volumes, the stock pushrods and tubes can also be retained. Compression can be set between 10.25 and 10.5, and the stock camshafts can also be used. The Sportsters are not under cammed in the same way that the Big Twins are. We recommend the existing 40mm CV carb with a Head Quarters jet kit for the 1986-2006 models, and the stock throttle body and injectors for the 2007 up EFI models. Carb models benefit from one of our programable ignition modules, and the fuel injected models require dyno tuning.
With the introduction of the rubbermount Sportster in 2004, Harley redesigned the 1200 cylinder heads. These are the best XL heads yet, superior even than the older Buell Thunderstorm heads. The valves, combustion chamber, and port design are the same as the Buell XB12 and the XR1200, and they are excellent raw material for porting. Our Head Quarters reworked heads utilise 1.900 intake valves and 1.625 exhaust valves, the same as used with our Harley-Davidson Twin Cam and Evolution Big Twin performance cylinder head upgrades. By using various readily available Wiseco forged pistons and/or decking the heads, we can set compression ratios anywhere between 8 and 12 to 1 with the 1200 engine! This covers any racing or turbo charged application, although typically we will use 10.5 and the stock cams for street use.