Differences

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--- techtalk:ref:svcproc26 [2020/03/02 04:21]
hippysmack [Direct Method]
+++ techtalk:ref:svcproc26 [2020/03/04 05:59]
hippysmack [Thunderstorm Heads]
@@ Line 3: / Line 3: @@
 ====== Squish Band ======
-The squish (AKA "quench") band refers to the area or areas, \\ where the piston comes very close to the cylinder head while passing through top dead center (TDC). ((http://www.hammerperf.com/ttcheckingsquish.shtml)) \\ {{:techtalk:ref:svcproc:squish_band_3_by_aswracing.jpg?direct&300|}} ((drawing by aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?t=1720575)) \\
+The squish (AKA "quench") band refers to the area or areas, \\ where the piston comes very close to the cylinder head while passing through top dead center (TDC). ((http://www.hammerperf.com/ttcheckingsquish.shtml)) \\
+{{:techtalk:ref:svcproc:squish_band_3_by_aswracing.jpg?direct&400|}} ((drawing by aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?t=1720575)) {{:techtalk:ref:svcproc:squish_band_by_aswracing.gif?direct&250|}} ((drawing by aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?t=715370)) \\
 Even though the fire has already been lit, these areas still contain unburned air/fuel mix as the piston arrives. \\
 The piston sandwiches the air/fuel up next to the head, causing it to "squish", and shoot out toward the flame front. \\
@@ Line 70: / Line 72: @@
 ====== Machined Squish Band ======
+Deciding ahead of time on the performance upgrades you want is important. \\
+When you prepare heads, the chamber wants to get bigger. \\
+This happens for a variety of reasons. \\
+The valves are sunk in the heads to gain (valve to valve) and (valve to piston) clearance. \\
+As well as correct valvetrain geometry, and they're heavily unshrouded to improve low lift flow. \\
+As in the head picture above, all these things increase chamber volume and makes the compression ratio lower. \\
+At the same time, moving up the power scale really calls for more compression, not less, as the cams you'll use bleed off more compression. \\
+You can deck the heads to drop the chamber volume somewhat, but that has limitations and bad side effects. \\
+However, the coarse adjustment for the CR needs to be the piston and head decking should only be used for fine adjustments. \\
+Therefore, if you do your conversion with the standard dished conversion pistons, you put some constraints on future performance work. \\
+You're simply not going to be able to run as much cam or do as much head work so long as those standard conversion pistons are in your motor. \\
+Check with your engine builder / supplier for further assistance if you're looking for a complete performance package. \\
 |  Piston and head with matched squish band. ((drawing by aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?t=1802811&page=3))  |
 |{{:techtalk:ref:svcproc:squish_band_9_by_aswracing.jpg?direct&300|}}|
+====== Reverse Dome ======
 A piston with a reverse dome has a dish in the middle of it. \\
@@ Line 98: / Line 117: @@
 |{{:techtalk:ref:svcproc:squish_band_6_by_aswracing.jpg?direct&300|}}| {{:techtalk:ref:svcproc:squish_band_7_by_aswracing.jpg?direct&300|}}|{{:techtalk:ref:svcproc:squish_band_8_by_aswracing.jpg?direct&300|}}|
-Deciding ahead of time on the performance upgrades you want is important. \\
+====== Lightning Heads ======
-When you prepare heads, the chamber wants to get bigger. \\
-This happens for a variety of reasons. \\
+S heads and the older (pre-rubber mount) SE heads, 96-98 Buell S1 heads, 97 Buell S3 heads, 97-98 Buell M2 heads and Buell Blast heads are the same. ((aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?t=715370)) \\
-The valves are sunk in the heads to gain (valve to valve) and (valve to piston) clearance. \\
+These are what we call "Lightning" heads. \\
-As well as correct valvetrain geometry, and they're heavily unshrouded to improve low lift flow. \\
+cc chamber with a 10° cast in squish shelf, 1.715/1.480 valve sizes, the old low floor, squared off bowl ports like all the hemi heads etc. \\
-As in the head picture above, all these things increase chamber volume and makes the compression ratio lower. \\
+All 1200S motors came with flat tops just like every other Evolution Sportster. \\
+The Lightning head was the first generation performance head from HD for the XL motor. \\
+All they did was take the Hemi head and add a bunch of material to the chamber to bring it down from 67cc to 62cc. \\
+And they dual plugged some of them (1200S and the later SE versions). Ports and valve sizes stayed the same as the hemi head.
+Bringing the chamber volume down like that, with no change in the piston (i.e. they stayed with flat tops), bumps the compression up. \\
+(from the stock 9:1 to about 10:1. That's the sole performance gain of a Lightning head) \\
+The problem with those heads was the way in which they added the material. When you just add material to a chamber like that, you shroud the valves. \\ Looking at the chambers, you see a whole lot of material around the valves. That obstructs low lift flow. \\
+====== Thunderstorm Heads ======
+Two years after the Lightning head, HD came out with the Thunderstorm head. \\
+In the Thunderstorm, they went back to 67cc , allowing them to unshroud the valves and a 15° cast in squish shelf. \\
+They paired it with a domed piston to get the compression up to 10:1. \\
+They also improved the ports and went to larger valve sizes (1.810" / 1.575"). This setup is head and shoulders better than the Lightning setup. \\
+The angled squish bands direct the fuel being squeezed out of the squish bands more directly at the flame front. ((aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?t=2206)) \\
+But the way it's done in the Thunderstorm, it's really rough. Since it's cast in, it's uneven. \\
+Typically from the factory the clearance is .050" or more, and that makes the squish band largely ineffective anyway. \\
+Thunderstorm heads are obsolete now. \\
+They could be machined nice and even, but there's a huge overhang around the perimeter. \\
+So to machine it, typically .035"-.045" had to be taken off the deck, sometimes more. \\
+Below is an example of before and after machining. This is much better with a nice even and consistent squish clearance. \\
+But cutting the deck this much has some side effects, like less valve to piston clearance. \\
+As well as potentially forcing the customer into short or adjustable pushrods. \\
+It also typically makes the chamber too small, forcing us to open it up in other areas. \\
+Also notice how there's not a whole lot of surface area. This squish band is effective up to about a .125" tall dome. \\
+Anything higher than that and the dome goes past the squish band. \\
+|  Stock Thunderstorm Heads ((photo by aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?t=2206))  |  Thunderstorms as Machined ((photo by aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?t=2206))  |
+|{{:techtalk:ref:svcproc:thunderstom_chamber_by_aswracing.jpg?direct&300|}}|{{:techtalk:ref:svcproc:thunderstorm_as_machined_by_aswracing.jpg?direct&300|}}|
+====== Buell XB/04XL Heads ======
+As delivered, they have flat squish bands with a 62cc chamber. ((aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?t=2206)) \\
+This lets you toss them on over flat tops and have a squish band with lots of area and 10:1 compression. Not a bad way to do it. \\
+If you want to angle it, it's not a problem, you've got lots of material to work with. \\
+You can make the squish band as big or small as you want. \\
+You can make it match the piston you're using exactly, do relief cuts with the rest of the material to help overlap flow if you want. \\
+You can do all this without excessive deck milling and all the problems that come with it. \\
+The stock valves are the same sizes as the Thunderstorms, 1.810" intake and 1.575" exhaust. \\
+The springs and guides can support up to .550" lift safely, though, versus .500" for the Thunderstorms. \\
+The ports are actually a little better than the Thunderstorms. \\
+The Thunderstorms were a major step forward from the Lightning/Screaming Eagle heads, but the XB/04 XL1200 heads are even better. \\
+|  Stock Buell XB Heads  ((photo by aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?t=2206))  |  Machined XB Heads ((photo by aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?t=2206))  |
+|{{:techtalk:ref:svcproc:buell_xb_heads_by_aswracing.jpg?direct&300|}}|{{:techtalk:ref:svcproc:buell_xb_heads_as_machined_by_aswracing.jpg?direct&300|}}|
-At the same time, moving up the power scale really calls for more compression, not less, as the cams you'll use bleed off more compression. \\
-You can deck the heads to drop the chamber volume somewhat, but that has limitations and bad side effects. \\
-However, the coarse adjustment for the CR needs to be the piston and head decking should only be used for fine adjustments. \\
-Therefore, if you do your conversion with the standard dished conversion pistons, you put some constraints on future performance work. \\
-You're simply not going to be able to run as much cam or do as much head work so long as those standard conversion pistons are in your motor. \\
-Check with your engine builder / supplier for further assistance if you're looking for a complete performance package. \\
 ====== Compression Ratio ======
@@ Line 157: / Line 228: @@
 In general, deck height has nothing to do with the squish band. \\
+In the example below with a 3-9/16" bore and the chamber is about 3" in diameter. \\
+Since you have a 3" diameter chamber over a 3-9/16" diameter bore, the head deck overhangs the bore by a little over 1/4" all the way around. \\
+Notice how the piston is a flat top for a little over 1/4" around it's perimeter. That's not an accident. \\
+If you look at the drawing below, \\
+You can see that cutting more off the deck isn't going to change the clearance between the top of the piston and the head deck. \\
+To change that clearance, you've got to use a thinner head gasket, or mill the top of the cylinder so the piston sits higher in it. \\
+(or use a thinner base gasket which accomplishes the same thing) \\
+{{:techtalk:ref:svcproc:stock_883_chamber_by_aswracing.jpg?direct&300|}} ((photo by aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?t=1720575)) {{:techtalk:ref:svcproc:bathtub_squish_by_aswracing.jpg?direct&400|}} ((drawing by aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?t=1720575)) \\
+\\
+However, there are situations where decking the head does change the squish clearance. \\
+Look at a Thunderstorm or Lightning head with their angled shelf and massive overhang for example. \\
+In the pic below, you see it's got a cast-in squish shelf. That shelf is angled, and the heads were paired with a piston that had a matching angle. \\
+But see that big overhang around the perimeter of the chamber? \\
+If you deck this head, you reduce or remove that overhang. That most definitely changes the squish clearance. \\
+So there are situations where decking does change the squish clearance and situations where it doesn't. \\
+{{:techtalk:ref:svcproc:stock_thunderstorm_chamber_by_aswracing.jpg?direct&300|}} ((photo by aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?t=1720575))  \\
 \\

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