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Flatheadbill
Posted on Saturday, August 09, 2014 - 05:22 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Hi. Usually on the tuber forum but recently acquired a Blast project. I have read that they use a Thunderstorm piston. Is a Thunderstorm head a reasonable update ? I would prefer an XB head but I have an X1 and several extra heads on the shelf. Any direction appreciated. Thanks, Bill
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Gearheaderiko
Posted on Saturday, August 09, 2014 - 08:17 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

I don't remember the details, I'll see if I can find my files. But...even if you put a thunderstorm head on, I'd get a new, better matched piston.
XB is the way to go though, but I definitely understand about having parts on the shelf.
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Gearheaderiko
Posted on Monday, August 11, 2014 - 01:28 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Sorry, I cant find the information. The link is now bad and although I printed it up, I cant find that either.
Revolution Performance or one of our other Badweb sponsors could probably help you provided:

they have the time
you realize they are in the business of selling, not providing free information.

I wish I could be of more help, but my brain will not access those files at this time. But it is out there on the web, somewhere.
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Ezblast
Posted on Wednesday, August 13, 2014 - 03:34 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

GENERAL INFO ...provided by Aaron Wilson of NRHS

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 1/8", 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 1/8". 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:

(to be added)

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.

03-PRESENT BUELL XB HEADS: This head is characterized by it's pear-shaped 62cc
bathtub chamber and large 1.810 intake/1.575 exhaust valves. 7mm valve stems
(versus 5/16 on prior heads) and small beehive springs were introduced on
these heads as well.

The 62cc chamber gives about a 10:1 compression ratio when used with flat top
pistons. NRHS offers a forged domed piston for this chamber to raise this to
10.5:1. The bathtub shape with flat (0 degree) squish bands eliminates the
core shift issues with the 15 degree cast squish bands of the Thunderstorm
heads, and also the bathtub shape allows the chamber to be sized down to 62cc
without excessive valve shrouding. Finally, the bathtub shape offers much
more material for machining in 15 or 30 degree dome cuts and or chamber
relief cuts, making this head an excellent candidate for effective chamber
work. Angling the squish band in an accurrate, machined fashion, improves on
a 0 degree setup by more directly aiming the fuel coming out of the squish
band at the flame front, and also reducing the shelf the air must go around
when entering or exiting the chamber.

Ports were improved over the Thunderstorm head by way of a more gradual,
constant arc in the roof through the bowl area, as well as a raised floor at
the inlet. Both of these things help reduce turbulence by reducing the length
difference between the roof and the floor, thus making the velocities at both
places closer to the same.

This head is 3.670" in height, which is .020 shorter than the prior XL and
Buell heads. by itself, this is not enough to necessitate shorter pushrods.
If the head is decked, and used with thin gaskets to optimize squish
clearance, pushrod length can become an issue.

These heads are ideal for 883 to 1200 conversions as they're all silver in
color, although we've been known to black powder coat them for 883R models.
As mentioned earlier, the carb mounting/breather holes need to be drilled and
tapped to use them on a Sportster (we provide this service for free for heads
purchased from us). The head is only sold disassembled, but NRHS offers them
fully assembled with high flow stainless valves for the same price that all
of the individual pieces cost at the dealer.

04-PRESENT XL1200R/C HEADS: These heads are identical to the 03-up Buell XB
heads, except that the carb mount/breather holes are already drilled and
tapped, and the finish is black with polished fins. Also, the rear XB head
has a provision for a head temp sensor, and this head does not, but this is
normally not needed on a Sportster application.

LATEST SE HEAD: These heads use the same casting as 04-up XL1200R/C heads. The
ports and valve sizes remain unchanged, and the flow rates are identical.

An additional .050" additional has been removed from the decks, which makes
them .070 shorter than 86-03 XL heads. This provides a 55cc chamber and
10.5:1 when used with flat tops. However, the decking is not without side
effects; in particular, short pushrods will likely be needed (available from
NRHS) and valve to piston clearance will become a concern when using cams
with more than stock overlap.

Also, these heads have different springs and valves. The valves are the same
size, 1.810" intake/1.575" exhaust, but are made of stainless steel. The
spring is a larger beehive with about 170lbs on the seat, versus about 135
for the stock head, and the spring pocket has been cut down about .120 to
allow more spring travel. This lowering of the seat pocket makes the roof of
the port thinner and limits how much it can be raised when the head is ported.

All of these heads are black with polished fins. A "Screamin Eagle" script has
been fastened to the front head in the area just above the pushrod tubes.
EZ
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Gearheaderiko
Posted on Wednesday, August 13, 2014 - 04:40 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

You found it
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Flatheadbill
Posted on Wednesday, August 13, 2014 - 10:40 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Thanks for the info.
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Blueblast
Posted on Thursday, August 14, 2014 - 12:38 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only) Ban Poster IP (Custodian/Admin only)

Just an FYI, Aaron is no longer with NRHS, he is now at Hammer Performance.

Talk about everything you could ever want to know about XL/Buell heads - wow!
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