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THE Harley Sportster

 

Sporty's: It's all about the head.


Keep in mind, that this in NOT our work....  This bit of information was found on www.harley-davidsonforums.com and was posted by  Aaron Wilson...  We thank him for his efforts in compiling this information and passing it along to the rest of the Sporty Community.

 

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 heads:

1986-1990 (4 speeds)
1991-2003 (5 speeds)
2004-present (rubber mounts)

Interchangeability:

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 diameter chamber.

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
more efficient 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 diecast heads.  
 
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 bowl.

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 XLH1200 head.

All Thunderstorm heads are black powder coated, without highlighted fins.
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 safe!!

 

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This information comes from the www.sportster.org website..   Thanks for sharing with the Sportster community!

 

Sportster and Buell Heads

Aaron Wilson

Screaming Eagle Sportster heads are what we call a "Lightning" head. They came out in 1996 on Buell S1 Lightning models, and a dual plug version came on the 1200S as well. They have the same size valves as a regular 1200 head: 1.715" intake & 1.480" exhaust, and the ports are the same. HD claims 8% better flow from the Screaming Eagle heads. But I've flowed a lot of heads, and I haven't seen it. Even identical heads vary pretty significantly from one to the next, and the range of numbers I get from 1200 heads and SE or Lightning heads is pretty much the same.

The big difference between a 1200 head and a Lightning head is the chamber. Where the 1200 head is a 67cc hemispherical chamber with no squish band, the Lightning head is a 62cc chamber with a pair of 10 degree squish bands. Note that these 10 degree squish bands don't do anything for you with a stock flat top piston. But the smaller volume of the Lightning chamber bumps the compression ratio up to about 10:1 with flat tops. That's really where the performance improvement of a Lightning head comes from.

The problem with Lightning heads, besides the ports and small valves, is that the extra material they put in the chamber to get the volume down tends to shroud the valves. The shrouding gets really bad when you start sticking big valves into the heads. When we do a 1.850" or 1.900" valve in a Lightning head, we always have to unshroud the valves quite a bit to get the low lift flow back. And that ends up taking the chamber bigger, often all the way back to 67cc where the 1200 head is. So then we have to either cut the hell out of the deck to get back to 62cc, or generally we recut the squish band to 15 degrees and put the customer into a set of Thunderstorm pistons, which is a better solution anyway because he gets a squish band. So essentially, we end up converting the Lightnings to Thunderstorms.

In 1998, Buell came out with the Thunderstorm head. It has improved ports as well as larger valves: 1.810" intake and 1.575" exhaust. The chamber is 67cc like the 1200 head, but it has a pair of 15 degree squish bands. So this chamber doesn't have so much material in it and they're able to put in big valves without shrouding them. It's a big improvement. If you put the Thunderstorms over flat tops, you'll have 9:1 compression with no squish just like you'd have with a 67cc 1200 head. But Buell paired these heads with a small 15 degree domed piston that gives 10:1 compression. All in all, it's a much better setup than the SE/Lightning heads. And the ports have some extra material where the Lightning heads really need it, so we're able to make a better port out of them. One downside to Thunderstorm heads on Sportsters though is that they're only available in black finish, no silver or black w/polished fins (not that some people don't convert them). Lightning heads have been made in all 3 finishes. Also, Thunderstorms have 7/16 NC front mounting holes, your Sportster uses 3/8, so you've got to drill the holes in your mount and swap your hardware, but that's pretty easy.

In 2003, Buell came out with the "XB" head. Same size valves as the Thunderstorms (1.810/1.575), but the valve stems are 7mm for less weight and the springs are conical style. They can easily support .550 of lift right out of the box, where all the older heads were only safe to about .500. They also have a 62cc bathtub chamber with a pair of flat squish bands. So now you can get 10:1 with your flat tops and have an effective squish band and big valves that aren't shrouded, and the best ports they've ever made (they tend to flow about the same as Thunderstorms but it's a less turbulent flow). In 2004, they put these heads onto the 1200 Sportsters as well, and they made them black with polished fins (the Buell XB heads are silver). Putting XB or 04XL1200 heads onto an 86-03 model isn't too bad, the only real issue is the front mounting bolts (front head), they moved the right front one inboard by a quarter inch and like the T-storms, the hardware is 7/16" as used on most Buells. So you've got to open up the holes in your front mounting bracket and elongate the right side one. If you go the XB (silver) route, you'll also have to mill/drill/tap your breather holes, the XB heads have the bosses but they're not prepared because the XB breathes out the top of the rocker box.  

 

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 safe!!

 

 

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