Unlike the Big Twins, there have been a lot of versions of Sportster and Buell heads offered over the years. This article is provided to shed some light on the differences between them.
The Evolution Sportster was introduced in the 1986 model year in both 883cc and 1100cc configurations. The difference between these displacements was the bore size: an 883 has a 3"
The cylinder heads you'll find on 1986-1990 models are:
A stock 1986 883 chamber is bathtub shaped and has a 49.5cc nominal volume This design provided a squish band over the stock flat top piston, the only year that an Evolution 883 had a squish band. The chamber on an 883 head is shallower than a 1200 chamber and therefore 883 valves are longer to match As a result the valves start out closer to the pistons and closer to each other.
The stock intake port on an 883 head has a low floor and a very squared off roof through the bowl that necks down to a tiny valve. This creates turbulence and results in poor flow. 883 heads have the same size ports as the 1100/1200 heads until it enters the bowl area, at which time it necks down to the small valve seats. The seats in an 883 head are notorious for being poorly blended into the bowl. A good competition valve job that opens up the seat i.d. and blends it into the bowl does wonders for an 883 head.The seats in any of the 883 heads are the same o.d. as the seats in the 87-03 1100/1200 heads. As such, they can be opened up to accommodate the larger 1.715"/1.480" valve sizes. Standard 1100/1200 valves are too short for the shallow 883 chambers, however, "conversion" valves are readily available that have the larger diameter heads and the longer 883 lengths.
87-90 XL883 Heads: 49.5cc chamber, 1.585" diameter intake valves, 1.350" diameter exhaust valves
1987 and later 883 heads have a 3" round, hemispherical chamber A squish band is still gained, however, when these heads are used over a 3.5" bore 1200 piston The chamber volume and valve sizes remained the same as the 1986 model. An "883" script was also added near the gasket surface . For 1987, the big change in the 883 head was the chamber shape. It became the 3" round, hemispherical shape that continues to this day. These heads, and the 5-speed versions, are very common and easy to come by, as many were taken off and replaced with 1200 heads when converting to a 1200. However, as noted above these heads make for a better conversion than the common 88-03 XL1200 head in a couple of ways.Most of these heads are silver, although some late model versions were made in black for specific models such as the XL883R.
1986 XL1100 Heads: 62cc chamber, 1.840" diameter intake valves, 1.610" diameter exhaust valves
These are ultra-rare Sportster heads and they were the best factory head ever made for a Sportster until the Thunderstorm head came out in 1998. They have very large valves and a pear-shaped chamber with flat squish bands on each side. The ports are not particularly good, though, with a low floor, sharp short side radius, and a squared off bowl. A good porting job makes these into a very fine performance head.
1987 XL1100 Heads: 62cc chamber, 1.715" diameter intake valves, 1.480" diameter exhaust valves
For 1987 the 1100 heads were given smaller valves. The chamber remained largely the same however. These heads are better than the 88-03 1200 heads just due to the better chamber.
88-90 XL1200 Heads: 67cc chamber, 1.715" diameter intake valves, 1.480" diameter exhaust valves
With the new larger 1200cc displacement for 1988, the chamber was enlarged and the squish bands eliminated to match the new 3.498" bore size and keep the compression ratio down. This results in an open, hemispherical chamber, with poor chamber turbulence (turbulence in the ports is bad, turbulence in the chamber is good). See below for pictures of the 91-03 version of this head which is almost the same thing.
1991-2003 (5-Speeds) and 1995-2002 Buell
For 1991, the Evolution Sportster got a new 5-speed transmission. HD also made changes to the valvetrain and crankcase breathing that affected the cylinder heads. The cams were relocated to sit directly under the lifters (4 speeds had them slightly offset) and the holes in the head where the pushrods pass through were moved to match. Also the crankcase breather was moved from the cam box cover to the bolts in the heads that had previously just held on the carb and air cleaner. This creates two issues when fitting 5-speed heads to a 4-speed:
1. Since the holes for the pushrod tubes are in a slightly different place, there's a potential for pushrod rub when 5-speed heads are put on a 4-speed or vice-versa
2. If you're going to take advantage of the 5-speed crankcase breathing, your 4-speed lower and middle rocker boxes will need to be swapped to 5-speed versions. Likewise if you're putting 4-speed heads onto a 5-speed, you'll need to modify your heads to allow breathing out the carb bolt holes (Hammer Performance can provide this service) or alternatively, use XB style rocker boxes.
91-03 XL883 Heads:49.5cc chamber, 1.585" diameter intake valves, 1.350" diameter exhaust valves
There are no significant differences between an 87-90 and a 91-03 883 head other than the pushrod hole locations and the crankcase breather provisions as described above.
91-03 XL1200 Heads:67cc chamber, 1.715" diameter intake valves, 1.480" diameter exhaust valves
There are no significant differences between an 88-90 and a 91-03 1200 head other than the pushrod hole locations and the crankcase breather provisions as described above.
This is one of the most common Sportster heads you'll come across, as it came on every 1200 Sportster from 1991 through 2003, except the 98-03 XL1200S model. Unfortunately, for performance applications it's not a particularly good head, as the ports are turbulent and the chamber is not, which is just exactly the opposite of what you want. See the pictures below for more information.
A stock 88-03 1200 head has a 3.5" diameter open hemispherical chamber and a 67cc nominal volume The lack of any squish band results in poor chamber turbulence and causes detonation issues at high compression ratios For this reason, many people prefer to prepare their 883 heads when doing an 883 to 1200 or 1250 conversion, rather than convert to this vintage of 1200 heads. This picture also shows the very squared off roof area through the bowl in both ports. Notice the sharp angle near the stamped numbers.
The stock intake port on an 88-03 XL1200 head is essentially the same as the 883’s intake port, except the bowl does not have to squeeze down to such a small valve. This is an improvement but it’s still not a very good port due to the low floor and squared off roof through the bowl.
95-96 Buell S2 Heads:67cc chamber, 1.715" diameter intake valves, 1.480" diameter exhaust valves
These heads were identical to the 91-03 XL1200 heads described above except that the spark plug side front motor mount bolt hole was 7/16-14 instead of 3/8-16. So be aware that not all Buell heads are higher performance than all Sportster heads.
96-03 Buell Lightning Heads:62cc chamber, 1.715" diameter intake valves, 1.480" diameter exhaust valves
In 1996 a new cylinder head was introduced on Buell S1 Lightning models. They were standard equipment on 1996-1998 S1 models (not S1W), 1997 S3 models, 1997-1998 M2 models, and 1998-2003 1200S Sportster Sport models. The Buell Blast uses a version of this head too. They were also available in the Screamin Eagle catalog, initially with a "Lightning" script in the fin area just below the rocker box, and later with a "Screamin Eagle" script. Versions were offered in silver as well as black with polished fins. Many of the black with polished fins versions (including those on the 1200S) had dual spark plugs as well. Buell versions of these heads use 7/16-14 bolt holes for the front mounting bracket while Sportster versions used 3/8-16.
The Lightning head has the same ports and valve sizes as the XL1200 heads of the same vintage and as such they flow exactly the same. The Screamin Eagle catalog at one time claimed 8% more flow but I've flow tested lots of them and the range of results I get is the same as the standard 88-03 XL1200 heads.
The one big difference in a Lightning head is that extra material was added to the chamber to reduce the size and raise the compression. Over a 1200cc flat top piston these heads give about 10:1 compression. The chamber material is cast into a 10 degree squish band, however, all of the bikes that had these heads from the factory used flat top pistons, so the squish band was ineffective. Hammer Performance offers an angled dome piston to match these heads and can even machine the squish band into a nice, even shape for maximum effectiveness - as cast, it's very rough and uneven.
The big down side to a Lightning head is that the extra material used to make the chamber smaller also ends up shrouding the valves badly. This hurts low-lift flow, and is especially bad when used with larger valves. When we do a SMASH or SLEDGE porting service to a Lightning head, we always unshroud the valves heavily to cure this problem.
98-02 Buell Thunderstorm Heads:67cc chamber, 1.810" diameter intake valves, 1.575" diameter exhaust valves
In 1998 a new cylinder head was introduced on Buell S1W and S3 models. In 1999 these heads were made standard equipment on all Buell models and they remained that way through the 2002 model year.
The Thunderstorm head has multiple improvements over the Lightning head. Not only are the valves significantly bigger, but the ports were improved as well, with a higher floor and a more gently radiused roof through the bowl area. The chamber was enlarged back to 67cc to unshroud the larger valves, and the squish band angle was changed to 15 degrees. These were paired with a factory piston to match and utilize the squish band, which HD had never done on Lightning heads.
A stock Thunderstorm chamber improves on the Lightning chamber by unshrouding the much larger valves. The squish band is also taken out to 15 degrees although it's still a rough, uneven casting with a lot of overhang around the perimeter, making it difficult to achieve a good squish clearance. The unshrouding resulted in a 67cc volume and requires a matching domed piston to get 10:1. Also, you can see in this picture how the roof through the bowl area is more gently radiused, as compared to the picture of the XL1200 chamber above. Look near the stamped numbers and compare.
The stock Thunderstorm intake port improves on the Lightning & 88-03 XL1200 intake port with a somewhat higher floor and more gentle radius through roof area in the bowl. Valve sizes were increased as well.