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techtalk:ref:svcproc26 [2020/03/02 04:46] hippysmack |
techtalk:ref:svcproc26 [2020/03/04 05:59] hippysmack [Thunderstorm 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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====== 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. \\ | + | 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)) \\ |
- | 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. \\ | + | 62cc 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 ====== | ====== Compression Ratio ====== | ||
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{{: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)) \\ | {{: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)) \\ | ||
+ | |||
+ | |||
\\ | \\ |