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techtalk:ref:svcproc26 [2020/03/02 04:20] hippysmack [Effects of Deck Height] |
techtalk:ref:svcproc26 [2020/03/04 04:58] hippysmack [Lightning Heads] |
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====== Squish Band ====== | ====== 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. \\ | 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. \\ | The piston sandwiches the air/fuel up next to the head, causing it to "squish", and shoot out toward the flame front. \\ | ||
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* Write the measurements down to conclude and average the squish band dimension. | * Write the measurements down to conclude and average the squish band dimension. | ||
- | | Solder held with grease. ((photo by aswracing of the XLFORUM )) | Remove the heads to reveal how far the solder was compressed. ((photos by JohnK of the XLFORUM http://xlforum.net/forums/showthread.php?p=3944070)) || | + | | Solder held with grease. ((photo by aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?t=1720575)) | Remove the heads to reveal how far the solder was compressed. ((photos by JohnK of the XLFORUM http://xlforum.net/forums/showthread.php?p=3944070)) || |
|{{:techtalk:ref:svcproc:squish_band_1_by_aswracing.jpg?direct&300|}}|{{:techtalk:ref:svcproc:checking_squish_1_by_johnk.jpg?direct&300|}}|{{:techtalk:ref:svcproc:checking_squish_2_by_johnk.jpg?direct&300|}}| | |{{:techtalk:ref:svcproc:squish_band_1_by_aswracing.jpg?direct&300|}}|{{:techtalk:ref:svcproc:checking_squish_1_by_johnk.jpg?direct&300|}}|{{:techtalk:ref:svcproc:checking_squish_2_by_johnk.jpg?direct&300|}}| | ||
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====== Machined Squish Band ====== | ====== 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)) | | | 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|}}| | |{{: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. \\ | A piston with a reverse dome has a dish in the middle of it. \\ | ||
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|{{: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|}}| | |{{: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. \\ | + | |
- | 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. \\ | + | 1200S 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)) \\ |
- | You can deck the heads to drop the chamber volume somewhat, but that has limitations and bad side effects. \\ | + | These are what we call "Lightning" heads. \\ |
- | However, the coarse adjustment for the CR needs to be the piston and head decking should only be used for fine adjustments. \\ | + | 62cc chamber with a 10° squish shelf, 1.715/1.480 valve sizes, the old low floor, squared off bowl ports like all the hemi heads etc. \\ |
+ | All 1200S motors came with flat tops just like every other Evolution Sportster. \\ | ||
- | Therefore, if you do your conversion with the standard dished conversion pistons, you put some constraints on future performance work. \\ | + | The Lightning head was the first generation performance head from HD for the XL motor. \\ |
- | 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. \\ | + | 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. | ||
- | Check with your engine builder / supplier for further assistance if you're looking for a complete performance package. \\ | + | 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. \\ | ||
====== Compression Ratio ====== | ====== Compression Ratio ====== | ||
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In general, deck height has nothing to do with the squish band. \\ | 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)) \\ | |
+ | |||
+ | |||
\\ | \\ |