It's all about the head.
in mind, that this in NOT our work.... This bit of information
was found on
www.harley-davidsonforums.com and was posted by
We thank him for his efforts in compiling this
information and passing it along to the rest of the Sporty
If you have
1986 (and maybe 1987) Sportster Heads, then please click (http://hammerperf.com/ttxlheads.shtml)
BEFORE proceeding!!! Some very important information about
these heads can be found there! (Thanks Pat!)
There are 3 generations of Evo Sportster
1986-1990 (4 speeds)
1991-2003 (5 speeds)
2004-present (rubber mounts)
Within a given generation, the heads are mechanically
interchangeable between the different models, i.e. all bolt holes
line up and no needed features are missing. Valve geometry is the
same: 27 degree intake & 31 degree exhaust for a 58 degree included
angle, and the location of the valve tips is the same.
The rocker box bolt pattern has not changed across any of these
generations; a 1986 lower rocker box will bolt right up to a 2006
head and vice-versa. The only thing you need to be aware of is that
the crankcase breathing arrangement has changed at each generation.
4-speed models provided no facility in the head for a crankcase
breather. 5-speed models incorporated crankcase
breathers into the carb mount bolts, and use a different middle
rocker box that has a check valve incorporated (aka "umbrella"
valve). Rubber mount models use an air/oil separator & check valve
unit bolted into the lower rocker box, and do away with the middle
rocker box, using a different top cover.
91-03 heads have been successfully fitted to 86-90 models. The major
difference you need to be aware of is that the spacing between the
pushrod holes is different between a 4 speed and a 5 speed. This is
because the cam box geometry is different and the pushrods are at a
different angle. So pay attention to the potential for pushrod rub
where they pass through the heads into the rocker box.
04-up heads have been successfully fitted to 91-03 models. The new
heads have the right front bolt hole relocated inboard 1/4", and
also use 7/16 fasteners as opposed to the 3/8 fasteners used on the
91-03 models. You can either modify your existing front mount, or
more recently a new mount has become available that solves this
issue. Also, be aware that the 04-up heads have larger fins and will
overhang 91-03 cylinders somewhat, most noticeable on the left side.
You can use your stock 91-03 rocker boxes or use the 04-up rocker
boxes, either will work fine.
Any time you're putting a different set of heads on your bike, you
need to be aware of the chamber size & shape and how it relates to
the piston you're using, to make sure they're mechanically
compatible and will give the desired compression ratio.
Buell Heads ...
There are 2 generations of Buell heads:
1995-2002 (tube frame models, aka "tubers")
2003-present (XB models)
95-02 Buell heads can be considered the same generation as 91-03
Sportster heads. The rocker box and head breather arrangements are
identical, as are the fin sizes. The front mount holes have the same
spacing as the 91-03 Sportster heads but use 7/16 NC fasteners
(exception: 95-96 S2 models which use a 3/8 fastener on one side and
a 7/16 fastener on the other).
03-present Buell heads can be considered the same generation as
04-present Sportster heads in that they use large fins and 7/16
front mount fasteners with the right front mount hole moved inboard
1/4". The main difference is that the XB head does not provide head
breather/carb mount bolt holes. The bosses are cast in, however, and
the holes can be drilled and tapped. Buell XB models don't need
these bolt holes due to the downdraft fuel injection system they
come with. Crankcase breathing is provided on stock XB models
through the tops of the rocker box covers.
SPECIFIC INFO ...
883 HEADS (ALL GENERATIONS): 883 heads all have a small, 49cc
chamber that's approximately 3" in diameter to match the 3" bore of
the 883. The chamber is also shallower than the chamber in any other
Sportster head. Valvetrain geometry is the same as the other heads
except that small 1.580" intake & 1.350" exhaust valves are used,
and the valves are longer to work with the shallower, smaller
In stock configuration, these are the worst ports of any XL head,
primarily due to the way the bowl area squeezes down to the small
diameter valve. This arrangement causes a lot of turbulence. The
heads respond well to a good porting and seat blending job,
particularly when used with a larger valve that better matches the
bowl size. The seats can accomodate the standard XLH1200 valve sizes
(1.715 intake/1.480 exhaust) and special longer "conversion valves"
are available to do this upgrade.
When used in an 883 to 1200 conversion, reverse dome (dish)
conversion pistons are available to give a workable compression
ratio. Alternatively, the chamber can be relieved and the heads used
with flat top pistons.
These heads have an advantage over the XLH1200 hemi chamber head in
that the 3" diameter chamber provides a "squish band" around it's
perimeter when placed over the larger 1200 bore. The squish band
results in more turbulence and a
chamber. However, the longer valves in these heads are also a
disadvantage in that piston to valve contact issues are much more
likely. Be concerned about this if the cams you're using have a high
TDC lift figure on one or both valves.
Most sets of 883 heads you come across will be silver in color. 883R
models have black 883 heads. All are easily identified by the "883"
script cast into them adjacent to the chamber.
86-87 XLH1100 HEADS:
1986-early 87, "Bathtub" heads.
Sand-cast construction. Extra large valves, 1.840" intake,
1.615" exhaust. Shaped combustion chamber with squish band.
9.0:1 compression. Sand-cast 1100 heads can not be mixed with
late 1987 , changed to die-cast construction (less expensive)
and round combustion chamber and valve sizes that were continued
thru to the 1200 heads. Valves 1.715 intake and 1.480 exhaust.
(Thanks to Tom Mack for the info on these 1986-87 heads!)
88-03 XLH1200 HEADS: These heads have a 67cc hemispherical chamber,
i.e. it's a round bowl with no squish band. Hemi chambers provide
maximum valve unshrouding but also tend to have poorer chamber
turbulence. The 67cc volume gives about 9:1 compression with flat
tops at 1200cc. Domed pistons are readily available to raise this
number up to 10:1 or higher. The pistons designed for this chamber
have a radiused edge on the domes to fit well inside the hemi
chamber shape, but the irregularity of the chamber (which is just a
casting) makes it impossible to achieve a good squish band.
Valve sizes are 1.715" intake and 1.480" exhaust. The stock seats
can support only slightly larger sizes, we fit them with 1.760"
intakes and 1.530" exhausts when doing a Stage 2 job (for Stage 3 we
change the seats).
The ports on these heads are not particularly good, they have
something of a squared off bowl and a low floor. In other words,
these are areas where they need more material.
These heads are all black with polished fins.
95-96 BUELL S2 HEADS: These heads are identical to the 88-03 XLH1200
heads in all respects except that one of the front mount bolt holes
is 7/16" NC instead of 3/8" NC. So don't be fooled; not all "Buell
Heads" are higher performance than Sportster heads.
96-03 LIGHTNING HEADS: This is a head that came out in 1996 on the
Buell S1 Lightning model, as well as the 1200S Sportster Sport
model. The 1200S version is black with polished fins and has dual
plugs, the second plug being accessible through the hole in the top
of the rocker box. The Buell S1 version is silver and has a single
spark plug. Versions of this head were also sold in the Screaming
Eagle catalog. Early versions were silver and carried the
"Lightning" script above the pushrod area. A version was sold in
black polished with no script. And finally, a black polished version
was sold with the "Screamin Eagle" script and dual plugs. Also, the
Buell Blast comes with a version of this head.
The valve sizes are 1.715" intake and 1.480" exhaust, identical to
the 88-03 XLH1200 head. The same seats are used, so Stage 2
Lightning heads get 1.760" intakes and 1.530" exhausts. The ports
are also identical to the 88-03 XLH1200 head. Later SE versions were
advertised as having 8% higher flow than stock XLH1200 heads, but as
someone who's flow tested lots of them, I just haven't seen it. the
range of numbers I get has been the same.
This only place this head is different from the 88-03 head is in the
chamber. Extra material was added, as well as a 10 degree squish
shelf, bringing the volume down to about 62cc. This gives around
10:1 when paired with flat top pistons. The squish band though does
nothing with a flat top. So the performance increase from this head
comes entirely from an extra point in compression ratio.
This extra material in the chamber somewhat shrouds the valves,
however, hurting low lift flow. It gets especially bad when oversize
valves are fitted. When putting larger valves into Lightning heads,
we always unshroud the chamber around the valve heavily to improve
flow. This of course raises the chamber volume and requires us to
deck the head significantly to get the volume back to 62cc. Often
we'll end up recutting the squish band to 15 degrees and just size
the chamber out to 67cc instead, and then put the customer into a
Thunderstorm type domed piston. We do, however, offer a 10 degree
piston designed for the stock Lightning head that offers 10.5:1
compression at 62cc.
98-02 BUELL THUNDERSTORM HEADS: This was the second generation high
performance head to come out on Buells. It was introduced in 1998 on
the S1W and S3/S3T (the S1 and the M2 retained the Lightning heads
in 1998). In 1999, all models came with Thunderstorms and it
remained that way through the 2002 model year.
This head went back to the 67cc volume and instead used a domed
piston to raise the compression ratio. The advantage to this is that
it heavily unshrouded the valves. A 15 degree squish shelf was
incorporated into the chamber and matched to a 15 degree dome angle
on the piston. Also, valve sizes were increased to 1.810" intake and
1.575" exhaust. Ports were improved as well, particularly in the
The squish shelf on a Thunderstorm head is still a casting, however,
and as such it's not very accurate. There's a good sized overhang
between the deck and the perimeter of the swuish shelf, and core
shift often makes the squish shelf uneven from side to side. So
while it's nice to have a squish shelf and the turbulence it
generates, it's effectiveness is limited unless you remachine it,
which generally requires .030 to .040 to be removed from the deck.
Still, this head performs substantially better than the Lightning or
All Thunderstorm heads are black powder coated, without highlighted
We get asked a lot about the different heads for Evo Sportsters. I
thought I'd put together a sticky to provide a reference for people.
This is gonna take a little bit, so please be patient as I revisit
the thread and edit it to add more information.
DISCLAIMER: This information has NOT been
verified and cannot be guaranteed to be accurate in any or all
respects. We have copied this information to our website to
make it easy to pass it along to Sportster owners. Please
verify this information with a reputable mechanic and/or machine
shop PRIOR to acting on it!!
Thanks and ride