These lightweight, but strong, forged pistons are the best choice for this popular conversion. The semi-slipper skirt design and short steel wristpins greatly reduce the overall weight of these assemblies, compared to the stock H-D 1200 pistons. They are close to the weight of the original 883 pistons, so have little influence on the crankshaft balance. The 883 combustion chambers are much smaller than those of the 1200, so increasing the 883 capacity to 1200 using regular flat top 1200 pistons causes an excessive compression increase. These Wiseco 1200 conversion pistons have a dish machined in the piston crown which controls the compression ratio.
We have these in 9,5-1 and 10-1 compression ratios to suit different applications. For most uses we favour the 10-1 version and retaining the standard camshafts. We also have oversizes available. We can also accurately bore and hone the existing 883 cylinders, which makes this a very cost effective and reliable Sportster performance upgrade.
These forged flat top pistons are for use in all year 1200 Evolution Sportsters with stock 1200 heads, as well as the earlier Buells that use stock H-D heads. These pistons, also available in oversizes, give 9-1 compression with the 88-03 heads, and 9.3-1 with the 04 up heads. We also use these with our Head Quarters 1200 valve 883 heads, and some of our Evolution Big Twin 89" stroker conversions. Compression is determined by the combustion chamber modifications. These pistons are not for use with the regular 883-1200 conversions with unmodified 883 heads.
These forged domed pistons give 10,5-1 compression with unmodified stock 1200 heads. Available in oversizes
These OEM cast pistons, also available in oversizes, have the correct 15 degree dome profile to match the combustion chamber shape of the Thunderstorm heads.
The Harley-Davidson Evolution Sportster has always proven to be excellent raw material for serious high performance upgrades, and as with other Harley engines we get to a point where a capacity increase makes perfect sense. Whilst the most common example of this is to bore the 883 cylinders out to 1200, to go bigger requires larger after market cylinders, sometimes also used in conjunction with a longer stroke crankshaft There are two bigger bore sizes that we use, 3 5/8" from S&S, and 3 13/16" from Axtell and Zippers. These give 79" and 88" capacity respectively, when used with the stock stroke crankshaft.
Both of these require the crankcases to be machined to accept the larger cylinder spigots as well as modifications to some cylinder heads to control compression. The 3 13/16 bore is the biggest that we can go to with the OEM crankases and cylinder stud bolt pattern, but we can also go larger still (4" bore) if we use aftermarket cases with a spread bolt pattern.
Whilst these big bore cylinder and piston kits also have a large labour content attached to their installation (engine out, stripped and reassembled, as well as crankcase machining and tuning), the advantage, for street use, is a serious torque increase. With the appropriate head work and camshaft choice, tailored to suit the intended use, these big bore conversions are very fast and reliable.
The cylinder and piston kits for the stock stroke crankshaft are available to suit all years of the Evolution Sportster, including the fuel injected rubbermount models.